Mark L Brusseau

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Books

• Brusseau, M. L. (2019). Environmental and Pollution Science, Third Edition. Academic Press.

Journals/Publications

• Brusseau, M. L. (2022). A Screening Model for Quantifying PFAS Leaching in the Vadose Zone and Mass Discharge to Groundwater. Advances In Water Resources.
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  Guo, B., J. Zeng, M.L. Brusseau, and Y. Zhang. A Screening Model for Quantifying PFAS Leaching in the Vadose Zone and Mass Discharge to Groundwater. Advances in Water Resources. 160, article 104102, 2022.
• Brusseau, M. L. (2022). PFAS Experts Symposium 2: Key Advances in Poly‐ and Perfluoroalkyl Characterization, Fate, and Transport. Remediation Journal.
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  Bryant, J.D., Anderson, R., Bolyard, S.C., Bradburne, J.T., Brusseau, M.L., Carey, G., Chiang, D., Gwinn, R., Hoye, B.R., Maher, T.L., McGrath, A.E., Schroeder, M., Thompson, B.R., and Woodward, D. PFAS Experts Symposium 2: Key Advances in Poly‐ and Perfluoroalkyl Characterization, Fate, and Transport. Remediation Journal
• Brusseau, M. L., & Guo, B. (2022). PFAS concentrations in soil versus soil porewater: Mass distributions and the impact of adsorption at air-water interfaces. Chemosphere, 302, 134938.
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  Determining the risk posed by PFAS leaching from soil to groundwater requires quantification of the magnitude and temporal/spatial variability of PFAS mass discharge from the vadose zone, which is governed in part by the concentrations of PFAS in soil porewater. Porewater concentrations are impacted and mediated by the properties of the PFAS and soil, multiple transport and fate processes, and site conditions. The objective of this research was to delineate the relationship between soil porewater concentrations and soil concentrations, based on a comprehensive model of PFAS mass distribution within a soil sample volume. Measured parameters representing solid-phase sorption and air-water interfacial adsorption are used to illustrate the impact of soil and PFAS properties on the distribution of representative PFAS between soil and soil porewater. Literature data reported for soil and soil porewater concentrations of several PFAS obtained from outdoor lysimeter experiments are used to test the distribution model. Soil-to-porewater concentration ratios predicted with the model compared very well to the measured concentration ratios. The nondimensional distribution coefficient that describes the distribution of PFAS mass amongst all domains within a soil sample was observed to be a function of PFAS molecular size. Numerical simulations conducted for a model fire-training source area were used to illustrate the ranges in magnitude of soil versus porewater concentrations for representative field conditions. The results of the measured and simulated data sets demonstrated the importance of air-water interfacial adsorption for the distribution of the longer-chain PFAS within soil samples. PFAS soil porewater concentrations are anticipated to range from ng/L to mg/L depending upon soil concentrations, which in turn depend upon the nature of the site.
• Hitzelberger, M., Khan, N. A., Mohamed, R. A., Brusseau, M. L., & Carroll, K. C. (2022). PFOS Mass Flux Reduction/Mass Removal: Impacts of a Lower-Permeability Sand Lens within Otherwise Homogeneous Systems. Environmental science & technology, 56(19), 13675-13685.
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  Perfluorooctane sulfonic acid (PFOS) is one of the most common per- and polyfluoroalkyl substances (PFAS) and is a significant risk driver for these emerging contaminants of concern. A series of two-dimensional flow cell experiments was conducted to investigate the impact of flow field heterogeneity on the transport, attenuation, and mass removal of PFOS. A simplified model heterogeneous system was employed consisting of a lower-permeability fine sand lens placed within a higher-permeability coarse sand matrix. Three nonreactive tracers with different aqueous diffusion coefficients, sodium chloride, pentafluorobenzoic acid, and β-cyclodextrin, were used to characterize the influence of diffusive mass transfer on transport and for comparison to PFOS results. The results confirm that the attenuation and subsequent mass removal of the nonreactive tracers and PFOS were influenced by mass transfer between the hydraulically less accessible zone and the coarser matrix (i.e., back diffusion). A mathematical model was used to simulate flow and transport, with the values for all input parameters determined independently. The model predictions provided good matches to the measured breakthrough curves, as well as to plots of reductions in mass flux as a function of mass removed. These results reveal the importance of molecular diffusion and pore water velocity variability even for systems with relatively minor hydraulic conductivity heterogeneity. The impacts of the diffusive mass transfer limitation were quantified using an empirical function relating reductions in contaminant mass flux (MFR) to mass removal (MR). Multi-step regression was used to quantify the nonlinear, multi-stage MFR/MR behavior observed for the heterogeneous experiments. The MFR/MR function adequately reproduced the measured data, which suggests that the MFR/MR approach can be used to evaluate PFOS removal from heterogeneous media.
• Huang, D., Khan, N. A., Wang, G., Carroll, K. C., & Brusseau, M. L. (2022). The Co-Transport of PFAS and Cr(VI) in porous media. Chemosphere, 286(Pt 3), 131834.
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  PFAS and Cr are present at some sites as co-contaminants. The objective of this research was to investigate the co-transport behavior of per- and polyfluoroalkyl substances (PFAS) and hexavalent chromium (Cr(VI)) in porous media. Miscible-displacement experiments were conducted using two soils and an aquifer sediment with different geochemical properties. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were employed as model PFAS. The retardation of PFOS was decreased in the presence of Cr(VI). Conversely, the transport and retardation of PFOA was not affected by the presence of Cr(VI). The reduction of PFOS retardation caused by Cr(VI) is likely due to sorption competition for both organic-carbon and inorganic (metal-oxides and clay minerals) domains. The relative contributions of the three soil constituents to PFOS sorption and the potential for competition between PFOS and Cr(VI) is a function of the geochemical composition of the porous media (i.e., organic carbon, metal-oxides and clay minerals). The PFAS had minimal impact on the retention and transport of Cr(VI). To our knowledge, the results presented herein represent the first reported data for PFOS and Cr(VI) co-transport in porous media. The results of this study indicate that the presence of Cr(VI) has the potential to increase the migration potential of PFOS in soil and groundwater, which should be considered when characterizing electroplating facilities, leather tanning facilities, and other co-contaminated sites.
• Huang, D., Saleem, H., Guo, B., & Brusseau, M. L. (2022). The impact of multiple-component PFAS solutions on fluid-fluid interfacial adsorption and transport of PFOS in unsaturated porous media. The Science of the total environment, 806(Pt 2), 150595.
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  The objective of this research was to investigate the impact of multiple-component PFAS solutions on the retention of PFOS during transport in unsaturated porous media. Surface tensions were measured to characterize the impact of co-PFAS on the surface activity of PFOS. Miscible-displacement experiments were conducted to examine the air-water interfacial adsorption of PFOS during transport in single and multi-PFAS systems. Literature data for transport of PFOS in NAPL-water systems were also investigated for comparison. A mathematical model incorporating surfactant-induced flow, nonlinear rate-limited sorption, nonlinear rate-limited fluid-fluid interfacial adsorption, and competitive adsorption at the fluid-fluid interface was used to simulate the transport of PFOS. The results indicate that the presence of co-PFAS had no measurable impact on solid-phase sorption of PFOS during transport under the extant conditions of the experiments. Conversely, the air-water interfacial adsorption of PFOS was decreased by the presence of co-PFAS during transport under unsaturated-flow conditions for relatively high input concentrations. The multiple-component Langmuir model could not predict the competitive adsorption behavior observed during transport. Conversely, competitive interactions were not observed for transport with a lower input concentration. The results indicate that the retention and transport of individual PFAS in mixtures may in some cases be impacted by the presence of co-PFAS due to competitive fluid-fluid interfacial adsorption effects. Reduced retention due to competitive interfacial-adsorption interactions has the potential to decrease PFOS retardation during transport, thereby increasing migration rates in sources zones and enhancing groundwater-pollution risks. SYNOPSIS: The impact of PFAS mixtures on the retention and transport of PFOS in unsaturated porous media is examined with a series of experiments and mathematical modeling.
• Johnson, G. R., Brusseau, M. L., Carroll, K. C., Tick, G. R., & Duncan, C. M. (2022). Global distributions, source-type dependencies, and concentration ranges of per- and polyfluoroalkyl substances in groundwater. The Science of the total environment, 841, 156602.
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  A meta-analysis was conducted of published literature reporting concentrations of per- and polyfluoroalkyl substances (PFAS) in groundwater for sites distributed in 20 countries across the globe. Data for >35 PFAS were aggregated from 96 reports published from 1999 to 2021. The final data set comprises approximately 21,000 data points after removal of time-series and duplicate samples as well as non-detects. The reported concentrations range over many orders of magnitude, from ng/L to mg/L levels. Distinct differences in concentration ranges are observed between sites located within or near sources versus those that are not. Perfluorooctanoic acid (PFOA), ranging from
• Lyu, Y., Wang, B., Du, X., Guo, B., & Brusseau, M. L. (2022). Air-water interfacial adsorption of C4-C10 perfluorocarboxylic acids during transport in unsaturated porous media. The Science of the total environment, 831, 154905.
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  The impact of chain length on air-water interfacial adsorption of perfluorocarboxylic acids (PFCAs) during transport in unsaturated quartz sand was investigated. Short-chain (C4-C7: PFBA, PFPeA, PFHxA, PFHpA) and long chain (C8-C10: PFOA, PFNA, PFDA) PFCAs were selected as a representative homologous series. Surface tensions were measured to characterize surface activities of the selected PFCAs. Miscible-displacement column experiments were conducted for each of the PFCAs to characterize the magnitudes of air-water interfacial adsorption under transport conditions. The transport of the long-chain PFCAs exhibited greater retardation than the short-chain PFCAs. Air-water interfacial adsorption (AWIA) was the predominant source of retention (≥63%) for the long-chain PFCAs. Conversely, AWIA contributed less to retention than did solid-phase sorption for the short-chain PFCAs, with the former contributions ranging from 4% to 40%. Direct examination of the breakthrough-curve profiles as well as mathematical-modeling results demonstrated that transport of the two longest-chain PFCAs was influenced by nonlinear AWIA, whereas that of the shorter-chain PFCAs was not. This disparate behavior is consistent with the input concentration used for the transport experiments in comparison to the respective surface activities and critical reference concentrations of the different PFCAs. Quantitative-structure/property-relationship (QSPR) analysis was applied to characterize the influence of molecular size on air-water interfacial adsorption. The logs of the air-water interfacial adsorption coefficients (K) determined from the transport experiments are a monotonic function of molar volume, consistent with prior QSPR analyses of surface-tension measured values. The K values determined from the transport experiments are very similar to those measured from surface-tension data, indicating that the transport experiments produced robust measurements of AWIA.
• Yan, N., Guo, Z., & Brusseau, M. L. (2022). Sucralose as an oxidative-attenuation tracer for characterizing the application of chemical oxidation for the treatment of 1,4-dioxane. Environmental science. Processes & impacts, 24(8), 1165-1172.
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  chemical oxidation (ISCO) has become a widely used soil and groundwater remediation method. Oxidative-attenuation tracers can be used to provide real-time, explicit delineation of contaminant mass-transfer and transformation behavior during an ISCO remediation project. The objective of this study was to evaluate the potential of employing sucralose, a widely used artificial sweetener, as an oxidative-attenuation tracer to characterize the remediation efficiency of 1,4-dioxane (dioxane) by persulfate-based ISCO. Batch and miscible-displacement experiments were conducted to examine the degradation rate and transport behavior of sucralose compared to that of dioxane. Comparable magnitudes and rates of degradation were observed for sucralose and dioxane in batch-reactor experiments with soil and persulfate. The breakthrough curves of sucralose and dioxane transport in a soil-packed column were coincident. The retardation factors were 1.1 for both compounds, indicating limited sorption for both sucralose and dioxane by the soil. Limited degradation was observed in the miscible-displacement experiments, consistent with the short residence time compared to the half-lives of sucralose and dioxane. Persulfate transport and decomposition behavior in the soil-packed columns was similar in the presence of sucralose or dioxane. A simulated tracer test was conducted to illustrate the application of sucralose as an oxidative-attenuation tracer at the pilot scale. These results demonstrate the potential of sucralose as an oxidative-attenuation tracer to support the robust design of ISCO applications for dioxane. The oxidative-attenuation tracer test method is anticipated to be an effective approach for characterizing mass-removal behavior of other emerging contaminants with appropriate selection of tracer.
• Zhang, Y., Brusseau, M. L., Neupauer, R. M., & Wei, W. (2022). General Backward Model to Identify the Source for Contaminants Undergoing Non-Fickian Diffusion in Water. Environmental science & technology, 56(15), 10743-10753.
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  Pollutant source identification (PSI) has been conducted for four decades for tracking Fickian diffusive pollutants, while PSI for non-Fickian diffusion, well-documented in aquifers and rivers, requires novel, predictive models. To enable PSI for non-Fickian diffusive pollutants, this study derived a general backward model using the fractional-adjoint approach in sensitivity analysis for dissolved contaminants with transport governed by the spatiotemporal fractional advection-dispersion equation (fADE). The backward fADE contains a self-adjoint time-fractional term for subdiffusion and direction-dependent, non-self-adjoint space-fractional terms for superdiffusion. Field applications showed that the resultant backward location probability density function identified the point source location in all three test cases, one alluvial aquifer and two rivers. The backward model and boundary conditions derived in this study made it possible to reliably and efficiently backtrack pollutants (and may include other constituents, such as bedload) undergoing mixed sub- and superdiffusion in natural aquatic systems. The classical PSI model, however, underestimated the source location since it did not account for solute retention and preferential flow. In addition, the measured tracer snapshots (if available before PSI) can enhance the parameter predictability and improve the applicability of backward fADE PSI. Most importantly, a spatially variable dispersion coefficient is needed in the backward fADE since PSI is most likely scale dependent in natural hydrologic systems.
• Brusseau, M. L. (2021). Examining the robustness and concentration dependency of PFAS air-water and NAPL-water interfacial adsorption coefficients.. Water research, 190, 116778. doi:10.1016/j.watres.2020.116778
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  Determining robust values for the air-water or NAPL-water interfacial adsorption coefficient, KIA, is key to characterizing and modeling PFAS transport and fate in several environmental systems. Direct, high-resolution measurements of surfactant adsorption at the fluid-fluid interface were aggregated from the literature. This data set was used to examine the accuracy and applicability of Γ and KIA measurements determined for three PFAS from transport experiments and surface-tension data. The transport-measured Γ and KIA data were observed to be fully consistent with the directly-measured data. Specifically, Γ values for the two methods were entirely coincident in the region of overlapping concentrations, which spanned ~4 orders-of-magnitude. Furthermore, the two data sets adhered to an identical Γ-C profile. These results conclusively demonstrate the accuracy of the transport-measured values. Γ and KIA values determined from the application of the Gibbs adsorption equation to measured surface-tension data were fully consistent with the directly-measured and transport-measured data sets, demonstrating their applicability for representing PFAS transport in environmental systems. The directly-measured data were used to examine the concentration dependency of KIA values, absent the potential confounding effects associated with the use of surface-tension or transport-measured data. The directly-measured data clearly demonstrate that KIA attains a constant, maximum limit at lower concentrations. Two separate analyses of the transport-measured data both produced observations of constant KIA values at lower concentrations, consistent with the directly-measured data. These outcomes are discussed in terms of surface activities, relative surface coverages, and critical concentrations.
• Brusseau, M. L. (2021). List of Published Peer-review Journal articles with complete citations. Multiple.
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  1. El Ouni, A., Guo, B., Zhong, H., and *Brusseau, M.L. Testing the Validity of the Miscible-Displacement Interfacial Tracer Method for Measuring Air-Water Interfacial Area: Independent Benchmarking and Mathematical Modeling. Chemosphere, 263, article 128193, 2021.2. Van Glubt, S., *Brusseau, M.L., Yan, N., Huang, D., Khan, N., and Carroll, K.C. Column versus Batch Methods for Measuring PFOS and PFOA Sorption to Geomedia. Environmental Pollution, 268, article 115917, 2021.3. Brusseau, M.L. Examining the Robustness and Concentration Dependency of PFAS Air-Water and NAPL-Water Interfacial Adsorption Coefficients. Water Research, 190, article 116778, 2021.4. Zhou, D., Brusseau, M.L., *Zhang, Y., Li, S., Wei, W., Sun, H., and Zheng, C. Simulating PFAS Adsorption Kinetics, Adsorption Isotherms, and Nonideal Transport in Saturated Soil with Tempered One-Sided Stable Density (TOSD) based Models. Journal of Hazardous Materials, 411, article 125169, 2021.5. Liu, Z., *Tan, H., and Brusseau, M.L. Significance of Isotopic and Geochemical Methods to Determine the Evolution of Inland Brackish and Bitter Water: An Example from the Zuli River in the Upper Reaches of the Yellow River, China. Hydrological Processes, 35, article e14024, 2021.6.Van Glubt, S. and *Brusseau, M.L. Contribution of Nonaqueous Phase Liquids the Retention and Transport of Per and Polyfluoroalkyl Substances (PFAS) in Porous Media. Environmental Science & Technology, 55, 3706-3715, 2021.7.Wang, Y., Khan, N., Huang, D., Carroll, K.C., and *Brusseau, M.L. Transport of PFOS in Aquifer Sediment: Transport Behavior and a Distributed-Sorption Model. Science of the Total Environment, 779, article 146444, 2021.8. Zhang, W., *Rao, W., Li, L., Brusseau, M.L., and Liu, Y. Adsorption of Cadmium onto Sand-Attapulgite Cutoff Wall Backfill Media. Water, Air, Soil Pollution, 232, article 47, 2021.9. Lu, J., *Lu, H., Brusseau, M.L., He, L., Gorlier, A., Yao, T., Tian, P., Feng, S., Yu, Q., Nie, Q., Yang, Y., Yin, C., Tang, M., Feng, W., Xue, Y., and Yin, F. Interaction of climate change, potentially toxic elements (PTEs), and topography on plant diversity and ecosystem functions in a high-altitude mountainous region of the Tibetan Plateau. Chemosphere, 275, article 130099, 2021.10. Pu, M., Wan, J., Zhang, F., Brusseau, M.L., Ye, D., and *Niu, J. Insight into Degradation Mechanism of Sulfamethoxazole by Metal-Organic Framework Derived Novel Magnetic Fe@C Composite Activated Persulfate. Journal of Hazardous Materials, 414, article 125598, 2021.11. *Brusseau, M.L. and Van Glubt, S. The Influence of Molecular Structure on PFAS Adsorption at Air-Water Interfaces in Electrolyte Solutions. Chemosphere, 281, article 130829, 2021.12. *Tran, T., Abrell, L., Brusseau, M.L., Chorover, J. Iron-Activated Persulfate Oxidation Degrades Aqueous Perfluorooctanoic Acid (PFOA) at Ambient Temperature. Chemosphere, 281, article: 130824, 2021.13. Cáñez, T.T., Guo, B., *McIntosh, J.C., Brusseau, M.L. Perfluoroalkyl and Polyfluoroalkyl substances (PFAS) in Groundwater at a Reclaimed Water Recharge Facility. Science of the Total Environment, 791, article 147906, 2021.14. *Pepper, I.L., Brusseau, M.L., Prevatt, F.J., Escobar, B.A. Incidence of PFAS in Soil Following Long-Term Application of Class B Biosolids. Science of the Total Environment, 791, article: 148449, 2021.15. Ji, Y., Yan, N., *Brusseau, M.L., Guo, B., Zheng, X., Dai, M., Liu, H., and Li, X. Impact of Hydrocarbon Surfactant on the Retention and Transport of Perfluorooctanoic Acid in Saturated and Unsaturated Porous Media. Environmental Science & Technology, 55, 10480−10490, 2021.16. *Brusseau, M.L., Guo, B., Huang, D., Yan, N., Lyu, Y. Ideal versus Nonideal Transport of PFAS in Unsaturated Porous Media. Water Research, 202, article 117405, 2021.17. *Brusseau, M.L. and Guo, B. Air-Water Interfacial Areas Relevant for Transport of Per and Poly-Fluoroalkyl Substances. Water Research, 207, article: 117785, 2021.18. Zeng, J., M.L. Brusseau, and B. *Guo. Model validation and analyses of parameter sensitivity and uncertainty for modeling long-term retention and leaching of PFAS in the vadose zone. Journal of Hydrology, 603, article 127172, 2021.
• Brusseau, M. L., & Guo, B. (2021). Air-water interfacial areas relevant for transport of per and poly-fluoroalkyl substances. Water research, 207, 117785.
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  Per and polyfluoroalkyl substances (PFAS) present in the soil pose a long-term threat to groundwater. Robust characterization and modeling of PFAS retention and transport in unsaturated systems requires an accurate determination of the magnitude of air-water interfacial area (AWIA). Multiple methods are available for measuring or estimating air-water interfacial area, including x-ray microtomography (XMT), various aqueous and gas-phase interfacial tracer-test (ITT) methods, and thermodynamic-based estimation methods. AWIAs determined with the different methods can vary significantly. Therefore, it is critical to determine which measurement methods are relevant for application to PFAS retention and transport. This is achieved by employing AWIAs determined with different methods to simulate the results of miscible-displacement experiments reported in the literature for the transport of perfluorooctanoic acid (PFOA) in an unsaturated quartz sand. Measured PFOA breakthrough curves were successfully predicted using AWIA values measured by aqueous ITT methods. Conversely, AWIAs measured with the XMT method and estimated with the thermodynamic method under-predicted the magnitude of retardation and could not successfully simulate the measured transport data. These results indicate that the ITT method appears to provide the most appropriate AWIA values for robust characterization and modeling of PFAS transport in unsaturated systems. The long-term impact of employing different AWIA values on PFOA leaching in the vadose zone was simulated for a representative AFFF application scenario. The predicted timeframes for PFOA migration to groundwater varied from 3 to 6 to 20 years depending on which AWIA was used in the simulation. These relatively large differences would result in significantly different risk-assessment outcomes. These results illustrate that it is critical to employ the AWIA that is most representative of PFAS retention for accurate predictions of PFAS leaching in the vadose zone.
• Glubt, S. V., Glubt, S. V., Brusseau, M. L., & Brusseau, M. L. (2021). Contribution of Nonaqueous-Phase Liquids to the Retention and Transport of Per and Polyfluoroalkyl Substances (PFAS) in Porous Media.. Environmental science & technology, 55(6), 3706-3715. doi:10.1021/acs.est.0c07355
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  Per and polyfluoroalkyl substances (PFAS) cocontamination with nonaqueous-phase organic liquids (NAPLs) has been observed or suspected at various sites, particularly at fire-training areas at which aqueous film-forming foams (AFFFs) were applied. The objectives of this study are to (1) delineate the relative significance of specific PFAS-NAPL processes on PFAS retention, including partitioning into the bulk NAPL phase and adsorption to the NAPL-water interface; (2) investigate the influence of NAPL properties, saturation, and mass-transfer constraints on PFAS retention; and (3) determine whether PFAS may impact NAPL distribution through mobilization or dissolution. Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are used as representative PFAS, and trichloroethene (TCE) and decane are used as representative NAPLs. NAPL-water interfacial adsorption was quantified with NAPL-water interfacial-tension measurements; partitioning into NAPL was quantified with batch experiments, and retardation factors (R) in the absence and presence of residual NAPL were determined with miscible-displacement transport experiments. R values increased in the presence of residual NAPL, with adsorption to the NAPL-water interface accounting for as much as ∼77% of retention and solid-phase adsorption also significantly contributing to retention. Additionally, this study provides the first QSPR analysis focused on NAPL-water interfacial adsorption coefficients, with results consistent with those from previous air-water studies. Lastly, this initial investigation into PFAS impacts on NAPL behavior determined that PFOS/PFOA are unlikely to enhance solubilization or mobilization of NAPL under the conditions present at many AFFF legacy sites.
• Glubt, S. V., Glubt, S. V., Brusseau, M. L., & Brusseau, M. L. (2021). The influence of molecular structure on PFAS adsorption at air-water interfaces in electrolyte solutions.. Chemosphere, 281, 130829. doi:10.1016/j.chemosphere.2021.130829
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  Fluid-fluid interfacial adsorption has been demonstrated to be an important retention process for per and polyfluoroalkyl substances (PFAS) in porous media with air or non-aqueous phase liquids (NAPLs) present. The objective of this study was to characterize the influence of PFAS molecular structure on air-water interfacial adsorption in electrolyte solutions. Measured and literature-reported surface-tension data sets were aggregated to generate the largest compilation of interfacial adsorption coefficients measured in aqueous solutions comprising environmentally representative ionic strengths. The surface activities and interfacial adsorption coefficients (Ki) exhibited chain length trends, with greater surface activities and larger Ki values corresponding to longer chain length. The impact of multiple-component PFAS solutions on the surface activity of a select PFAS was a function of the respective surface activities and concentrations. Quantitative structure-property relationship analysis (QSPR) employing a single molecular descriptor (molar volume) was used successfully to characterize the impact of PFAS molecular structure on air-water interfacial adsorption. A previously reported QSPR model based on PFAS data generated for deionized-water solutions was updated to include more than 60 different PFAS, comprising all head-group types and a wide variety of tail structures. The QSPR model developed for PFAS in electrolyte solution compared favorably to the model developed for deionized water. Additionally, the magnitude of ionic strength for non-zero ionic strength systems was determined to have relatively minimal impact on interfacial adsorption coefficients. The new QSPR model is therefore anticipated to be representative for a wide variety of PFAS and for a wide range of ionic compositions.
• Tan, H., Liu, Z., & Brusseau, M. L. (2021). Significance of isotopic and geochemical methods to determine the evolution of inland brackish and bitter water: An example from the Zuli river in the upper reaches of the Yellow River, China. Hydrological Processes, 35(1). doi:10.1002/hyp.14024
• Tran, T., Chorover, J., Brusseau, M. L., & Abrell, L. (2021). Iron-activated persulfate oxidation degrades aqueous Perfluorooctanoic acid (PFOA) at ambient temperature.. Chemosphere, 281, 130824. doi:10.1016/j.chemosphere.2021.130824
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  Perfluorooctanoic acid (PFOA, C8HF15O2) is an industrial surfactant that is highly resistant to natural breakdown processes such as those mediated by heat, hydrolysis, photolysis, and biodegradation. Many efforts have been developed to breakdown PFOA to less harmful species due to its widespread human exposure and potential toxicity. However, these methods require high temperature or specialized equipment with serious disadvantages of high energy cost for long-term use. We investigated the effectiveness of PFOA degradation by ferrous iron-activated persulfate oxidation (IAPO) under various aqueous geochemical conditions. Approximately 64% of PFOA (initial concentration = 1.64 μmol L-1) was degraded after 4 h under illuminated anoxic conditions at ambient temperature. This degradation rate and magnitude support the potential use of IAPO as a novel inexpensive and environmentally friendly method to remediate PFOA in soil and groundwater.
• Wang, Y., Wang, Y., Khan, N. A., Khan, N. A., Huang, D., Huang, D., Carroll, K. C., Carroll, K. C., Brusseau, M. L., & Brusseau, M. L. (2021). Transport of PFOS in aquifer sediment: Transport behavior and a distributed-sorption model.. The Science of the total environment, 779, 146444. doi:10.1016/j.scitotenv.2021.146444
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  The objectives of this research were to examine the transport of perfluorooctane sulfonic acid (PFOS) in aquifer sediment comprising different geochemical properties, and to compare the behavior to that observed for PFOS transport in soil and sand. PFOS retardation was relatively low for transport in all aquifer media. The PFOS breakthrough curves were asymmetrical and exhibited extensive concentration tailing, indicating that sorption/desorption was significantly nonideal. The results of model simulations indicated that rate-limited sorption/desorption was the primary cause of the nonideal PFOS transport. Comparison of PFOS transport in aquifer media to data reported for PFOS transport in two soils and a quartz sand showed that PFOS exhibited more extensive elution tailing for the soils, likely reflecting differences in the relative contributions of various media constituents to sorption. A three-component distributed-sorption model was developed that accounted for contributions from soil organic carbon, metal oxides, and silt + clay fraction. The model produced very good predictions of Kd for the five media with lower soil organic‑carbon contents (≤0.1%). Soil organic carbon was estimated to contribute 19-42% of the total sorption for all media except the sand, to which it contributed ~100%. The contribution of silt + clay ranged from 51 to 80% for all media except the sand. The only medium for which the contribution of metal-oxides was significant is Hanford, with an estimated contribution of 15%. Overall, the results of the study indicate that sorption of PFOS by these aquifer media comprised contributions from multiple soil constituents.
• Yan, N., Khan, N. A., Huang, D., Glubt, S. V., Carroll, K. C., & Brusseau, M. L. (2021). Column versus batch methods for measuring PFOS and PFOA sorption to geomedia.. Environmental pollution (Barking, Essex : 1987), 268(Pt B), 115917. doi:10.1016/j.envpol.2020.115917
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  The objective of this study is to compare the consistency between column and batch experiment methods for measuring solid-phase sorption coefficients and isotherms for per and polyfluoroalkyl substances (PFAS). Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are used as representative PFAS, and experiments are conducted with three natural porous media with differing geochemical properties. Column-derived sorption isotherms are generated by conducting multiple experiments with different input concentrations (multi-C0 method) or employing elution-front integration wherein the entire isotherm is determined from a single breakthrough curve (BTC) elution front. The isotherms generated with the multi-C0 column method compared remarkably well to the batch isotherms over an aqueous concentration range of 3-4 orders of magnitude. Specifically, the 95% confidence intervals for the individual isotherm variables overlapped, producing statistically identical regressions. The elution-front integration isotherms generally agreed with the batch isotherms, but exhibited noise and systematic deviation at lower concentrations in some cases. All data sets were well described by the Freundlich isotherm model. Freundlich N values ranged from 0.75 to 0.81 for PFOS and was 0.87 for PFOA and are consistent with values reported in the literature for different geomedia. The results of this study indicate that column and batch experiments can measure consistent sorption isotherms and sorption coefficients for PFOS and PFOA when robust experimental setup and data analysis are implemented.
• Yan, N., Lyu, Y., Huang, D., Guo, B., & Brusseau, M. L. (2021). Ideal versus Nonideal Transport of PFAS in Unsaturated Porous Media.. Water research, 202, 117405. doi:10.1016/j.watres.2021.117405
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  Per- and poly-fluoroalkyl substances (PFAS) adsorb at air-water interfaces during transport in unsaturated porous media. This can cause surfactant-induced flow and enhanced retention that is a function of concentration, which complicates characterization and modeling of PFAS transport under unsaturated conditions. The influence of surfactant-induced flow and nonlinear air-water interfacial adsorption (AWIA) on PFAS transport was investigated with a series of miscible-displacement transport experiments conducted with a several-log range in input concentrations. Perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and ammonium perfluoro 2-methyl-3-oxahexanoate (GenX) were used as model PFAS. The results were interpreted in terms of critical reference concentrations associated with PFAS surface activities and their relationship to the relevancy of transport processes such as surfactant-induced flow and nonlinear AWIA for concentration ranges of interest. Analysis of the measured transport behavior of PFAS under unsaturated-flow conditions demonstrated that AWIA was linear when the input concentration was sufficiently below the critical reference concentration. This includes the absence of significant arrival-front self-sharpening and extended elution tailing of the breakthrough curves, as well as the similarity of retardation factors measured for a wide range of input concentrations. Independently-predicted simulations produced with a comprehensive flow and transport model that accounts for transient variably-saturated flow, surfactant-induced flow, nonlinear rate-limited solid-phase sorption, and nonlinear rate-limited AWIA provided excellent predictions of the measured transport. A series of simulations was conducted with the model to test the specific impact of various processes potentially influencing PFOS transport. The simulation results showed that surfactant-induced flow was negligible and that AWIA was effectively linear when the input concentration was sufficiently below the critical reference concentration. PFAS retention associated with AWIA can be considered to be ideal in such cases, thereby supporting the use of simplified mathematical models. Conversely, apparent nonideal transport behavior was observed for experiments conducted with input concentrations similar to or greater than the critical reference concentration.
• Yu, Q., Yin, F., Yin, C., Yao, T., Yang, Y., Xue, Y., Tian, P., Tang, M., Nie, Q., Lu, J., Lu, H., He, L., Gorlier, A., Feng, W., Feng, S., & Brusseau, M. L. (2021). Interaction of climate change, potentially toxic elements (PTEs), and topography on plant diversity and ecosystem functions in a high-altitude mountainous region of the Tibetan Plateau.. Chemosphere, 275, 130099. doi:10.1016/j.chemosphere.2021.130099
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  Potentially toxic elements (PTEs) generated from mining activities have affected ecological diversity and ecosystem functions around the world. Accurately assessing the long-term effects of PTEs is critical to classifying recoverable areas and proposing management strategies. Mining activities that shape geographical patterns of biodiversity in individual regions are increasingly understood, but the complex interactions on broad scales and in changing environments are still unclear. In this study, we developed a series of empirical models that simulate the changes in biodiversity and ecosystem functions in mine-affected regions along elevation gradients (1500-3600 m a.s.l) in the metal-rich Qilian Mountains (∼800 km) on the northeastern Tibetan Plateau (China). Our results confirmed the crucial role of PTEs dispersal, topography, and climatic heterogeneity in the diversification of plant community composition. On average, 54% of the changes in ecosystem functions were explained by the interactions among topography, climate, and PTEs. However, merely 30% of the changes were correlated with a single driver. The changes in species composition (explained variables = 94.8%) in the PTE-polluted habitats located in the warm and humid low-elevation deserts and grasslands were greater than those occurring in the dry alpine deserts and grasslands. The ecosystem functions (soil characteristics, nutrient migration, and plant biomass) experienced greater changes in the humid low-elevation grasslands and alpine deserts. Our results suggest that the processes driven by climate or other factors can result in high-altitude PTE-affected habitat facing greater threats.
• Zhang, F., Ye, D., Wan, J., Pu, M., Niu, J., & Brusseau, M. L. (2021). Insight into degradation mechanism of sulfamethoxazole by metal-organic framework derived novel magnetic Fe@C composite activated persulfate. Journal of Hazardous Materials, 414. doi:10.1016/j.jhazmat.2021.125598
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  Abstract Novel Fe@C composites derived from metal-organic framework (MOF) were synthesized. Being subject to pyrolysis under different temperatures endows these Fe@Cs diverse physical-chemical properties, including morphology, crystal structure, defect level, magnetism, and most importantly, iron phase composition. Fe@C-800 consists mainly of Fe3C and α-Fe, thus possesses strong ferromagnetic properties, which imparts the ability to be separated and recycled. Its catalytic activity towards the activation of persulfate (PS) and the decomposition of sulfamethoxazole (SMX) was found to be the best among all the Fe@Cs, and this activity can be regenerated by simple heat treatment. Given the mixed form of iron and N-doped carbon, α-Fe/Fe3C species provide electrons for PS to decompose and generate sulfate radical (SO4·-), hydroxyl radical (·OH), and superoxide radical (O2·-), initiating the radical pathway for partial SMX degradation. The positively charged C atoms on PS bonded Fe@C, as well as the conversion of O2·- give rise to the generation of singlet oxygen (1O2), which was responsible for the non-radical pathway for SMX degradation. As a consequence, SMX was degraded to intermediates through five degradation pathways, and finally mineralized to inorganic molecules. The results indicate that Fe@C-800 has great potential to serve as a promising activator for persulfate-mediated environmental remediation.
• Zhang, W., Zhang, W., Rao, W., Rao, W., Liu, Y., Liu, Y., Li, L., Li, L., Brusseau, M. L., & Brusseau, M. L. (2021). Adsorption of Cadmium onto Sand-Attapulgite Cutoff Wall Backfill Media. Water Air and Soil Pollution, 232(2). doi:10.1007/s11270-021-04981-z
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  The adsorption of Cd by sand-attapulgite cutoff wall backfill media was investigated with batch experiments for different quantities of attapulgite in the mixture (30%, 40%, 60%, and 100%; dry weight). The adsorption capacity of the media for Cd increased with the increase of attapulgite content (Ap). The change of adsorbed amount (qt) with time (t) exhibited two-stage behavior, with more than 80% of the final qt attained in the first 30 min of the experiments. The Elovich equation was the most suitable for describing the adsorption kinetics of Cd by the sand-attapulgite media. The isotherm data were best fit by the Freundlich equation. Analysis of the results indicates that cation exchange was the major adsorption mechanism. The theoretical maximum adsorption capacities (qm) of the sand-attapulgite media for Cd calculated by the Langmuir isotherm model are 6311 mg/kg (Ap = 30%), 6437 mg/kg (Ap = 40%), 6534 mg/kg (Ap = 60%), and 7034 mg/kg (Ap = 100%). The removal percentage (RP) and the distribution coefficient (Kd) of Cd decreased with the increase of the initial Cd concentration (C0) in the solution. An empirical equation for predicting Kd in terms of Ap and C0 was developed: log(Kd) = − 1.22log(C0) + 0.71Ap + 4.17 (r2 = 0.924). This equation can be used to estimate the distribution coefficient of Cd for sand-attapulgite backfill media. This will provide valuable parameters for the study of Cd transport in the sand-attapulgite cutoff wall media, and for the design of such systems for management of landfill leachate.
• Zhong, H., Ouni, A. E., Guo, B., & Brusseau, M. L. (2021). Testing the Validity of the Miscible-Displacement Interfacial Tracer Method for Measuring Air-Water Interfacial Area: Independent Benchmarking and Mathematical Modeling.. Chemosphere, 263, 128193. doi:10.1016/j.chemosphere.2020.128193
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  Abstract The interfacial tracer test (ITT) conducted via aqueous miscible-displacement column experiments is one of a few methods available to measure air-water interfacial areas for porous media. The primary objective of this study was to examine the robustness of air-water interfacial area measurements obtained with interfacial tracer tests, and to examine the overall validity of the method. The potential occurrence and impact of surfactant-induced flow was investigated, as was measurement replication. The column and the effluent samples were weighed during the tests to monitor for potential changes in water saturation and flux. Minimal changes in water saturation and flux were observed for experiments wherein steady flow conditions were maintained using a vacuum-chamber system. The air-water interfacial areas measured with the miscible-displacement method completely matched interfacial areas measured with methods that are not influenced by surfactant-induced flow. This successful benchmarking was observed for all three media tested, and over a range of saturations. A mathematical model explicitly accounting for nonlinear and rate-limited adsorption of surfactant at the solid-water and air-water interfaces as well as the influence of changes in surface tension on matric potentials and flow was used to simulate the tracer tests. The independently-predicted simulations provided excellent matches to the measured data, and revealed that the use of the vacuum system minimized the occurrence of surfactant-induced flow and its associated effects. These results in total unequivocally demonstrate that the miscible-displacement ITT method produced accurate and robust measurements of air-water interfacial area under the extant conditions.
• Zhou, D., Zhou, D., Zheng, C., Zheng, C., Zhang, Y., Zhang, Y., Wei, W., Wei, W., Sun, H., Sun, H., Li, S., Li, S., Brusseau, M. L., & Brusseau, M. L. (2021). Simulating PFAS adsorption kinetics, adsorption isotherms, and nonideal transport in saturated soil with tempered one-sided stable density (TOSD) based models.. Journal of hazardous materials, 411, 125169. doi:10.1016/j.jhazmat.2021.125169
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  Reliable quantification of per- and polyfluoroalkyl substances (PFAS) adsorption and mobility in geomedia provides critical information (i.e., evaluation and prediction) for risk characterization and mitigation strategy development. Given the limited PFAS data available and various competing theories for modeling pollutant kinetics, it is indispensable to better understand and quantify the adsorption and transport of PFAS in geomedia using generalized models built upon a consistent physical theory. This study proposed a universal physical law (called the tempered stable law) in PFAS adsorption/transport by interpreting PFAS adsorption kinetics and nonideal transport as a nonequilibrium process dominated by adsorption/desorption with multiple rates following the tempered one-sided stable density (TOSD) distribution. This universal TOSD function led to novel TOSD-based models which were then tested by successfully simulating PFAS adsorption kinetics, adsorption isotherms, and nonideal transport data reported in the literature. Model comparisons and extensions were also discussed to further check the feasibility of the TOSD models and their adaptability to capture PFAS transport in more complex geomedia at all scales.
• Araujo, J. B., & Brusseau, M. L. (2020). Assessing XMT-Measurement Variability of Air-Water Interfacial Areas in Natural Porous Media. Water resources research, 20(1).
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  This study investigates the accuracy and reproducibility of air-water interfacial areas measured with high-resolution synchrotron x-ray microtomography (XMT). Columns packed with one of two relatively coarse-grained monodisperse granular media, glass beads or a well-sorted quartz sand, were imaged over several years, encompassing changes in acquisition equipment, improved image quality, and enhancements to image acquisition and processing software. For the glass beads, the specific solid surface area (SSSA-XMT) of 31.6 ±1 cm determined from direct analysis of the segmented solid-phase image data is statistically identical to the independently calculated geometric specific solid surface area (GSSA, 32 ±1 cm) and to the measured SSSA (28 ±3 cm) obtained with the NBET method (NBET). The maximum specific air-water interfacial area (A) is 27.4 (±2) cm, which compares very well to the SSSA-XMT, GSSA, and SSSA-NBET values. For the sand, the SSSA-XMT (111 ±2 cm) and GSSA (113 ±1 cm) are similar. The mean A is 96 ±5 cm, which compares well to both the SSSA and the GSSA values. The XMT-SSSA values deviated from the GSSA values by 7-16% for the first four experiments, but were essentially identical for the later experiments. This indicates that enhancements in image acquisition and processing improved data accuracy. The A values ranged from 74 cm to 101 cm, with a coefficient of variation (COV) of 9%. The maximum capillary interfacial area ranged from 12 cm to 19 cm, for a COV of 10%. The COVs for both decreased to 5-6% for the latter five experiments. These results demonstrate that XMT imaging provides accurate and reproducible measurements of total and capillary interfacial areas.
• Brusseau, M. L. (2020). Comparison of Manganese Dioxide and Permanganate as Amendments with Persulfate for Aqueous 1,4-Dioxane Oxidation. Water, 12, article 3061.
• Brusseau, M. L. (2020). Efficient Removal of Trichloroethene in Oxidative Environment by Anchoring nano FeS on Reduced Graphene Oxide Supported nZVI Catalyst: The Role of FeS on Oxidant Decomposition and Iron Leakage.. Journal of Hazardous Materials, 392, article 122328.
• Brusseau, M. L. (2020). Scale Issues and the Effects of Heterogeneity on the Dune-induced Hyporheic Mixing. Journal of Hydrology, 590, article 125429.
• Brusseau, M. L. (2020). Simulating PFAS transport influenced by rate-limited multi-process retention. Water research, 168, 115179.
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  The transport of per- and poly-fluoroalkyl substances (PFAS) in the vadose zone is complicated by the fact that multiple mass-transfer processes can contribute to their retention and retardation. In addition, PFAS transport at some sites can be further complicated by the presence of organic immiscible liquids (OIL). Mass-transfer processes are inherently rate limited and, therefore, have the potential to cause nonideal transport of PFAS. The objectives of this research were to: (1) develop a solute-transport model that explicitly accounts for multiple retention processes, including adsorption at air-water and OIL-water interfaces, adsorption by the solid phase, and diffusive mass-transfer between advective and nonadvective domains, and (2) apply the model to measured transport data to delineate which processes are rate limited and contribute to observed nonideal transport. Breakthrough curves for transport of two PFAS and one hydrocarbon surfactant in sand obtained from prior miscible-displacement experiments exhibited nonideal transport. The multiprocess model effectively simulated the measured transport data. The results of the analyses indicate that adsorption at the air-water and OIL-water interface can generally be treated as effectively instantaneous for transport in porous media. The rate limitations associated with solid-phase adsorption and diffusive mass transfer between advective and nonadvective domains were of greater significance.
• Brusseau, M. L., & Taghap, H. (2020). NAPL-Water Interfacial Area as a Function of Fluid Saturation Measured with the Interfacial Partitioning Tracer Test Method.. Chemosphere, 260, article 127562.
• Brusseau, M. L., Anderson, R. H., & Guo, B. (2020). PFAS concentrations in soils: Background levels versus contaminated sites. The Science of the total environment, 740, 140017.
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  Per- and polyfluoroalkyl substances (PFAS) are contaminants of critical concern due to their persistence, widespread distribution in the environment, and potential human-health impacts. In this work, published studies of PFAS concentrations in soils were compiled from the literature. These data were combined with results obtained from a large curated database of PFAS soil concentrations for contaminated sites. In aggregate, the compiled data set comprises >30,000 samples collected from >2500 sites distributed throughout the world. Data were collected for three types of sites- background sites, primary-source sites (fire-training areas, manufacturing plants), and secondary-source sites (biosolids application, irrigation water use). The aggregated soil-survey reports comprise samples collected from all continents, and from a large variety of locations in both urban and rural regions. PFAS were present in soil at almost every site tested. Low but measurable concentrations were observed even in remote regions far from potential PFOS sources. Concentrations reported for PFAS-contaminated sites were generally orders-of-magnitude greater than background levels, particularly for PFOS. Maximum reported PFOS concentrations ranged upwards of several hundred mg/kg. Analysis of depth profiles indicates significant retention of PFAS in the vadose zone over decadal timeframes and the occurrence of leaching to groundwater. It is noteworthy that soil concentrations reported for PFAS at contaminated sites are often orders-of-magnitude higher than typical groundwater concentrations. The results of this study demonstrate that PFAS are present in soils across the globe, and indicate that soil is a significant reservoir for PFAS. A critical question of concern is the long-term migration potential to surface water, groundwater, and the atmosphere. This warrants increased focus on the transport and fate behavior of PFAS in soil and the vadose zone, in regards to both research and site investigations.
• Brusseau, M. L., Lyu, Y., Yan, N., & Guo, B. (2020). Low-concentration tracer tests to measure air-water interfacial area in porous media. Chemosphere, 250, 126305.
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  The aqueous-based interfacial tracer method employing miscible-displacement tests is one method available for measuring air-water interfacial areas. One potential limitation to the method is the impact of tracer-induced drainage on the system. The objective of this study was to investigate the efficacy of a low-concentration tracer test method for measuring air-water interfacial area. Tracer concentrations and analytical methods were selected that allowed the use of tracer input concentrations that were below the threshold of tracer-induced drainage. Multiple tracer tests were conducted at different water saturations. Interfacial areas increased from 34.8 to 101 cm with the decrease in saturation from 0.86 to 0.62. The method produced relatively robust measurements of air-water interfacial area, with coefficients of variation ranging from 6 to 26%. A variably saturated flow and transport model that accounts for the effects of tracer on interfacial tension, and the retention of tracer at the air-water and solid-water interfaces, was used to test for potential tracer-induced drainage. The simulations showed that the use of low tracer-input concentrations eliminated this phenomenon. This is consistent with the measured data for effluent-sample masses, which exhibited minimal change during the tests, and with the observation that the interfacial areas obtained with the low-concentration-tracer method were consistent with values measured with two methods that are not influenced by tracer-induced drainage. These results demonstrate that the low-concentration miscible-displacement tracer test method is an effective approach for measuring air-water interfacial areas in porous media.
• Guo, B., Zeng, J., & Brusseau, M. L. (2020). A Mathematical Model for the Release, Transport, and Retention of Per- and Polyfluoroalkyl Substances (PFAS) in the Vadose Zone. Water resources research, 56(2).
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  Per- and Polyfluoroalkyl Substances (PFAS) are emerging contaminants of critical concern. As surfactants, PFAS tend to accumulate at air-water interfaces and may stay in the vadose zone for long times before contaminating groundwater. Yet not well understood, the extent of retention in the vadose zone has critical implications for risk management and remediation strategies. We present the first mathematical model that accounts for surfactant-induced flow and solid-phase and air-water interfacial adsorption. We apply the model to simulate PFOS (a PFAS compound of primary concern) transport in the vadose zone at a model fire-training area site impacted by Aqueous Film-Forming Foam (AFFF). Air-water interfacial adsorption is shown to have a significant impact-amplified by the low water content due to gravity drainage-total retardation factors range from 233 to 1355 for the sand and 146 to 792 for the soil used in the study. The simulations illustrate it can take several decades or longer for PFOS to reach groundwater. Counterintuitively, the lower water content in the sand-due to stronger drainage and weaker capillary retention-leads to retardation factors greater than for the soil. Also, most PFOS is adsorbed at air-water interfaces with only 1-2% in the aqueous phase. The implications include 1) fine-texture materials could have lower retardation factors than sand due to higher retained water content, 2) soil PFAS concentrations are likely to be orders of magnitude higher than those in groundwater at source zones. Both implications are consistent with recent field observations at hundreds of AFFF-impacted sites.
• Guo, Z., Russo, A. E., DiFilippo, E. L., Zhang, Z., Zheng, C., & Brusseau, M. L. (2020). Mathematical modeling of organic liquid dissolution in heterogeneous source zones. Journal of contaminant hydrology, 235, 103716.
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  A simple one-dimensional heterogeneous-source model was used to simulate dissolution of organic liquid that was non-uniformly distributed in physically heterogeneous porous media. The permeability field was depicted as a pseudo-homogeneous medium. The source zone was discretized into multiple domains representing different organic-liquid configurations and hydraulic accessibilities, each with a different representative upscaled mass transfer rate coefficient that is temporally variable. This simplified approach represents a system where minimal information is available regarding system heterogeneities. All factors that influence dissolution were incorporated into the calibrated mass transfer terms. The mass transfer terms were calibrated for each zone separately. The one-dimensional, heterogeneous-source model adequately simulated the multi-stage dissolution behavior observed for column-scale systems that were packed with different natural soils, as well as for flow-cell systems wherein the source zone consisted of both a residual zone and pool. The results indicate that the model adequately simulated the presence of multiple organic-liquid zones in porous media with different configurations and hydraulic accessibilities, which accounts for the non-ideal dissolution behavior observed. The calibrated mass transfer terms for each source type were consistent with those obtained for systems that contained only one of either source type.
• Jiang, H., Guo, B., & Brusseau, M. L. (2020). Characterization of the Micro-scale Surface Roughness Effect on Immiscible Fluids and Interfacial Areas in Porous Media Using the Measurements of Interfacial Partitioning Tracer Tests. Advances in water resources, 146.
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  This study presents a model-based methodology to characterize the surface roughness effect on immiscible fluids in porous media using the measurements obtained with the gas-phase interfacial partitioning tracer test (IPTT). The characterization approach captures how adsorbed wetting film configuration on grain surfaces influences fluid-fluid interfaces in unsaturated porous media. The method establishes a novel representation of surface and interface roughness that delineates the micro-scale fractal nature of grain surfaces and the fluid-surface interactions at these scales. The method was tested using reported experimental data for several soils. The results showed that the methodology was effective for natural porous media comprising a range of physical and geochemical properties. Comparisons between characterized parameters of different media revealed that micro-scale surface roughness was only partially correlated to soil texture properties. Images of the test media obtained with scanning electron microscopy (SEM) illustrates the complexity of micro-scale surface roughness, and its variability among different media. Tests with an organic liquid-water system validated the generalness of surface roughness properties generated by the model. The proposed methodology is anticipated to provide a means to characterize and quantify the effects of surface roughness on fluid-solid interaction and fluid-fluid interfacial area, which are critical to various environmental disciplines.
• Jiang, H., Guo, B., & Brusseau, M. L. (2020). Pore-Scale Modeling of Fluid-Fluid Interfacial Area in Variably Saturated Porous Media Containing Microscale Surface Roughness. Water resources research, 56(1).
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  A pore-scale model is developed to simulate fluid-fluid interfacial area in variably saturated porous media, with a specific focus on incorporating the effects of solid-surface roughness. The model is designed to quantify total (film and meniscus) fluid-fluid interfacial area ( ) over the full range of wetting-phase fluid saturation ( ) based on the inherent properties of the porous medium. The model employs a triangular pore space bundle of cylindrical capillaries (BCC) framework, modified with three surface roughness-related parameters. The first parameter (surface roughness factor) represents the overall magnitude of surface roughness, whereas the other two parameters (interface growth factor and critical adsorptive film thickness) reflect the micro-scale structure of surface roughness. A series of sensitivity analyses was conducted for the controlling variables, and the efficacy of the model was tested using air-water interfacial area data measured for three natural porous media. The model produced good simulations of the measured data over the full range of saturation. The results demonstrate that total interfacial areas for natural media are typically much larger than those for ideal media comprising smooth surfaces due to the substantial contribution of surface roughness to wetting-film interfacial area. The degree to which fluid-fluid interfacial area is influenced by roughness is a function of fluid-retention characteristics and the nature of the rough surfaces. The full impact of roughness may be masked to some degree due to the formation of thick wetting films, which is explicitly quantified by the model. Application of the model provides insight into the importance of the interplay between pore-scale distribution and configuration of wetting fluid and the surface properties of solids.
• Khan, A. Z., Khan, S., Ayaz, T., Brusseau, M. L., Khan, M. A., Nawab, J., & Muhammad, S. (2020). Popular wood and sugarcane bagasse biochars reduced uptake of chromium and lead by lettuce from mine-contaminated soil. Environmental pollution (Barking, Essex : 1987), 263(Pt A), 114446.
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  As a result of metal mining activities in Pakistan, toxic heavy metals (HMs) such as chromium (Cr) and lead (Pb) often enter the soil ecosystem, accumulate in food crops and cause serious human health and environmental issues. Therefore, this study examined the efficacy of biochar for contaminated soil remediation. Poplar wood biochar (PWB) and sugarcane bagasse biochar (SCBB) were amended to mine-contaminated agricultural soil at 3% and 7% (wt/wt) application rates. Lactuca sativa (Lettuce) was cultivated in these soils in a greenhouse, and uptake of HMs (Cr and Pb) as well as biomass produced were measured. Subsequently, health risks were estimated from uptake data. When amended at 7%, both biochars significantly (P
• Lyu, Y., & Brusseau, M. L. (2020). The influence of solution chemistry on air-water interfacial adsorption and transport of PFOA in unsaturated porous media. The Science of the total environment, 713, 136744.
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  There is great interest in the transport behavior of PFAS in the vadose zone, and the impact of leaching on groundwater contamination. Air-water interfacial adsorption is an important process for PFAS retention in unsaturated porous media, and it is influenced by many factors including solution conditions such as ionic strength. The present study employed miscible-displacement column experiments to investigate the impact of ionic strength and pH on perfluorooctanoic acid (PFOA) retardation and transport under dynamic water-flow conditions. The results showed that retardation under unsaturated conditions was affected significantly by changes in ionic strength, whereas there was minimal impact for saturated conditions. This indicates that air-water interfacial adsorption, which was a major source of retardation, was influenced significantly by changes in ionic strength while they had a minor impact on solid-phase adsorption. The impact of changes in ionic strength on the magnitude of air-water interfacial adsorption observed for the column experiments was consistent with measured surface-tension data. The impact of changes in pH was less significant compared to that of ionic strength for transport under unsaturated conditions. These results illustrate the influence of solution chemistry on PFAS adsorption and transport under unsaturated conditions. This solution-dependent behavior should be considered when characterizing PFAS transport in soils and the vadose zone.
• Meng, L., Zuo, R., Brusseau, M. L., Wang, J. S., Liu, X., Du, C., Zhai, Y., & Teng, Y. (2020). Groundwater pollution containing ammonium, iron and manganese in a riverbank filtration system: Effects of dynamic geochemical conditions and microbial responses. Hydrological processes, 34(22), 4175-4189.
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  Bench-scale experiments were conducted to investigate the effect of hydraulic loadings and influent concentration on the migration and biotransformation behavior of three groundwater pollutants: ammonium (NH), iron (Fe) and manganese (Mn). Columns packed with aquifer media collected from a river bank filtration (RBF) site in Harbin City, NE China were introduced synthetic groundwater (SGW) or real groundwater (RGW) were at two different constant flow rates and initial contaminant concentrations to determine the impact of system conditions on the fate of the target pollutants biotransformation. The results showed that the biotransformation rate of Fe Mn, and NH decreased by 8%, 39% and 15% under high flow rate (50 L d) compared to low flow rate (25 L d), which was consistent with the residence-time effect. While the biotransformation rate of Fe Mn, and NH decreased by 7%, 14% and 9% under high influent concentration compared to original groundwater. The 16S rRNA analysis of the aquifer media at different depths after experiments completion demonstrated that the relative abundance of major functional microbes iron oxidizing bacteria (IOB) and manganese oxidizing bacteria (MnOB) under higher flow rate and higher influent concentration decreased 13%, 14% and 25%, 24%, respectively, whereas the ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) exhibited minimal change, compared to the lower flow rate. Above all results indicated that both high flow rate and high concentration inhibit the biotransformation of NH, Fe and Mn. The biotransformation of Fe and Mn occurs primarily in the 0-40 cm and 20-60 cm depth intervals, respectively, whereas the NH biotransformation appears to occur relatively uniformly throughout the whole 110cm column. The biotransformation kinetics of NH in RGW and SGW, Mn in RGW at different depths accords with the first order kinetics model, while Fe in RGW and SGW, Mn in SGW presented more complicated biotransformation process. The results should improve understanding of the transport and fate of common groundwater pollutants in riverbank filtration and other groundwater recharge environments.
• Pu, M., Niu, J., Brusseau, M. L., Sun, Y., Zhou, C., Deng, S., & Wan, J. (2020). Ferrous metal-organic frameworks with strong electron-donating properties for persulfate activation to effectively degrade aqueous sulfamethoxazole. Chemical engineering journal (Lausanne, Switzerland : 1996), 394.
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  Three novel persulfate activators, Fe(II)-based metal-organic frameworks (MOFs) were synthesized for the degradation of sulfamethoxazole (SMX). The degradation experiment results showed that all the Fe(II)MOFs could effectively activate persulfate and degrade more than 97% SMX within 180 min, with higher than 77% persulfate decomposition efficiencies. It was found by Mössbauer spectra that the variation of organic ligands for synthesis have an influence on the content of Fe(II) of these MOFs, thus resulted in the order of activation capacities: Fe(Nic) > Fe(PyBDC) > Fe(PIP). It was demonstrated that the activation of persulfate was mainly ascribed to the heterogeneous process that accomplished by surface-bounded Fe(II) acted as the main active site to provided electrons for persulfate or dissolved oxygen. EPR and molecular probe studies confirmed the coexistence of SO·, ·OH, and O·, and differentiated their contributions in SMX degradation. Possible degradation pathways of SMX were proposed based on the detection results of intermediates by UPLC-MS/MS. This work provides a new prospect into the synthesis of high-performance MOFs with strong electron-donating properties as efficient persulfate activators, which may encourage the employ of MOFs in the wastewater treatment process.
• Yan, N., Ji, Y., Zhang, B., Zheng, X., & Brusseau, M. L. (2020). Transport of GenX in Saturated and Unsaturated Porous Media. Environmental science & technology, 54(19), 11876-11885.
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  The objective of this research was to investigate the retention and transport behavior of GenX in five natural porous media with similar median grain diameters but different geochemical properties. Surface tensions were measured to characterize surface activity. Miscible-displacement experiments were conducted under saturated conditions to characterize the magnitude of solid-phase adsorption, while unsaturated-flow experiments were conducted to examine the impact of air-water interfacial adsorption on retention and transport. The results from surface-tension measurements showed that the impact of solution composition is greater for the ammonium form of GenX than for the acid form, due to the presence of the NH counterion. The breakthrough curves for the experiments conducted under saturated conditions were asymmetrical, and a solute-transport model employing a two-domain representation of nonlinear, rate-limited sorption provided reasonable simulations of the measured data. The magnitudes of solid-phase adsorption were relatively small, with the highest adsorption associated with the medium containing the greatest amount of metal oxides. The breakthrough curves for the experiments conducted under unsaturated conditions exhibited greater retardation due to the impact of adsorption at the air-water interface. The contributions of air-water interfacial adsorption to GenX retention ranged from ∼24% to ∼100%. The overall magnitudes of retardation were relatively low, with retardation factors < ∼3, indicating that GenX has significant migration potential in soil and the vadose zone. To our knowledge, the results presented herein represent the first reported data for solid-water and air-water interfacial adsorption of GenX by soil. These data should prove useful for assessing the transport and fate behavior of GenX in soil and groundwater.
• Araujo, J. B., & Brusseau, M. L. (2019). Novel fluid-fluid interface domains in geologic media. ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS, 21(1), 145-154.
• Bagheri, H., Abyaneh, H. Z., Izady, A., & Brusseau, M. L. (2019). Modeling the transport of nitrate and natural multi-sized colloids in natural soil and soil amended with vermicompost. GEODERMA, 354.
• Brusseau, M. L. (2019). Estimating the relative magnitudes of adsorption to solid-water and air/oil-water interfaces for per- and poly-fluoroalkyl substances. ENVIRONMENTAL POLLUTION, 254.
• Brusseau, M. L. (2019). The influence of molecular structure on the adsorption of PFAS to fluid-fluid interfaces: Using QSPR to predict interfacial adsorption coefficients. WATER RESEARCH, 152, 148-158.
• Brusseau, M. L., & Van, G. S. (2019). The influence of surfactant and solution composition on PFAS adsorption at fluid-fluid interfaces. WATER RESEARCH, 161, 17-26.
• Brusseau, M. L., Khan, N., Wang, Y., Yan, N. i., Van, G. S., & Carroll, K. C. (2019). Nonideal Transport and Extended Elution Tailing of PFOS in Soil. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 53(18), 10654-10664.
• Brusseau, M. L., Yan, N. i., Van, G. S., Wang, Y., Chen, W., Lyu, Y., Dungan, B., Carroll, K. C., & Holguin, F. O. (2019). Comprehensive retention model for PFAS transport in subsurface systems. WATER RESEARCH, 148, 41-50.
• Farooq, U., Danish, M., Lyu, S., Brusseau, M. L., Gu, M., Zaman, W. Q., Qiu, Z., & Sui, Q. (2019). The impact of surface properties and dominant ions on the effectiveness of G-nZVI heterogeneous catalyst for environmental remediation. SCIENCE OF THE TOTAL ENVIRONMENT, 651, 1182-1188.
• Guo, Z., Brusseau, M. L., & Fogg, G. E. (2019). Determining the long-term operational performance of pump and treat an the possibility of closure for a large TCE plume. JOURNAL OF HAZARDOUS MATERIALS, 365, 796-803.
• Guo, Z., Fogg, G. E., Brusseau, M. L., LaBolle, E. M., & Lopez, J. (2019). Modeling groundwater contaminant transport in the presence of large heterogeneity: a case study comparing MT3D and RWhet. HYDROGEOLOGY JOURNAL, 27(4), 1363-1371.
• Hard, H. R., Brusseau, M., & Ramirez-Andreotta, M. (2019). Assessing the feasibility of using a closed landfill for agricultural graze land. ENVIRONMENTAL MONITORING AND ASSESSMENT, 191(7).
• Jiang, W., Tang, P., Lyu, S., Brusseau, M. L., Xue, Y., Zhang, X., Qiu, Z., & Sui, Q. (2019). Enhanced redox degradation of chlorinated hydrocarbons by the Fe(II)-catalyzed calcium peroxide system in the presence of formic acid and citric acid. JOURNAL OF HAZARDOUS MATERIALS, 368, 506-513.
• Milavec, J., Tick, G. R., Brusseau, M. L., & Carroll, K. C. (2019). 1,4-Dioxane cosolvency impacts on trichloroethene dissolution and sorption. ENVIRONMENTAL POLLUTION, 252, 777-783.
• Sun, Y., Lyu, S., Brusseau, M. L., Tang, P., Jiang, W., Gu, M., Li, M., Lyu, Y., Qiu, Z., & Sui, Q. (2019). Degradation of trichloroethylene in aqueous solution by nanoscale calcium peroxide in the Fe(II)-based catalytic environments. SEPARATION AND PURIFICATION TECHNOLOGY, 226, 13-21.
• Tang, P., Jiang, W., Lyu, S., Brusseau, M. L., Xue, Y., Qiu, Z., & Sui, Q. (2019). Mechanism of carbon tetrachloride reduction in ferrous ion activated calcium peroxide system in the presence of methanol. CHEMICAL ENGINEERING JOURNAL, 362, 243-250.
• Xue, Y., Sui, Q., Brusseau, M. L., Zhou, W., Qiu, Z., & Lyu, S. (2019). Insight into CaO2-based Fenton and Fenton-like systems: Strategy for CaO2-based oxidation of organic contaminants. CHEMICAL ENGINEERING JOURNAL, 361, 919-928.
• Yan, N. i., Zhong, H., & Brusseau, M. L. (2019). The natural activation ability of subsurface media to promote in-situ chemical oxidation of 1,4-dioxane. WATER RESEARCH, 149, 386-393.
• Arthur, J., Brusseau, M. L., & Dontsova, K. (2018). Dissolution and Transport of Insensitive Munitions Formulations IMX-101 and IMX-104 in Saturated Soil Columns. Science of the Total Environment, 624, 758-768.
• Brusseau, M. L. (2018). Assessing the potential contributions of additional retention processes to PFAS retardation in the subsurface. SCIENCE OF THE TOTAL ENVIRONMENT, 613, 176-185.
• Brusseau, M. L., & Guo, Z. (2018). The Integrated Contaminant Elution and Tracer Test Toolkit, ICET3, for Improved Characterization of Mass Transfer, Attenuation, and Mass Removal. Journal of Contaminant Hydrology, 208, 17-26.
• Brusseau, M. L., Carroll, K. C., Guo, Z., & Mainhagu, J. (2018). Borehole diffusive flux apparatus for characterizing diffusive mass-transfer in subsurface systems. ENVIRONMENTAL EARTH SCIENCES, 77(18).
• Duncan, C. M., & Brusseau, M. L. (2018). An assessment of correlations between chlorinated VOC concentrations in tree tissue and groundwater for phytoscreening applications. SCIENCE OF THE TOTAL ENVIRONMENT, 616, 875-880.
• Duncan, C., Mainhagu, J., Lin, D., & Brusseau, M. L. (2017). Analysis of Trichloroethene (TCE) Vapour in Soil-Gas Samples using Solid-Sorbent Tubes with Gas Chromatography/Mass Spectrometry. Environmental Chemistry, 14, 495-501.
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  ***Note: this publication has a 2017 publication date, but it was not assigned volume and page numbers until early 2018. Hence, it was not included in my 2017 annual review; it is included here for completeness.
• Khan, M. A., Ding, X., Khan, S., Brusseau, M. L., Khan, A., & Nawab, J. (2018). The influence of various organic amendments on the bioavailability and plant uptake of cadmium present in mine-degraded soil. SCIENCE OF THE TOTAL ENVIRONMENT, 636, 810-817.
• Lyu, Y., Brusseau, M. L., Chen, W., Yan, N. i., Fu, X., & Lin, X. (2018). Adsorption of PFOA at the Air-Water Interface during Transport in Unsaturated Porous Media. ENVIRONMENTAL SCIENCE & TECHNOLOGY, 52(14), 7745-7753.
• Pu, M., Guan, Z., Ma, Y., Wan, J., Wang, Y., Brusseau, M. L., & Chi, H. (2018). Synthesis of iron-based metal-organic framework MIL-53 as an efficient catalyst to activate persulfate for the degradation of Orange G in aqueous solution. APPLIED CATALYSIS A-GENERAL, 549, 82-92.
• Rahman, Z., Khan, B., Khan, H., Brusseau, M. L., & Ahmad, I. (2017). Assessment of Fluoride Contamination in Groundwater of District Mardan in Pakistan. Fluoride, 50, 445-454.
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  ***Note: this publication has a 2017 publication date, but it was not assigned volume and page numbers until early 2018. Hence, it was not included in my 2017 annual review; it is included here for completeness.
• Rehman, Z. U., Khan, S., Shah, M. T., Brusseau, M. L., Khan, S. A., & Mainhagu, J. (2018). Transfer of Heavy Metals from Soils to Vegetables and Associated Human Health Risks at Selected Sites in Pakistan. PEDOSPHERE, 28(4), 666-679.
• Virgone, K. M., Ramirez-Andreotta, M., Mainhagu, J., & Brusseau, M. L. (2018). Effective integrated frameworks for assessing mining sustainability. ENVIRONMENTAL GEOCHEMISTRY AND HEALTH, 40(6), 2635-2655.
• Xiaori, F., D, D., Brusseau, M. L., & S, L. (2018). Enhanced effect of EDDS and hydroxylamine on Fe(II)-catalyzed SPC system for trichloroethylene degradation. Environmental Science and Pollution Research, 25, 15733-15742.
• Xue, Y., Sui, Q., Brusseau, M. L., Zhang, X., Qiu, Z., & Lyu, S. (2018). Insight on the generation of reactive oxygen species in the CaO2/Fe(II) Fenton system and the hydroxyl radical advancing strategy. CHEMICAL ENGINEERING JOURNAL, 353, 657-665.
• Yan, N. i., Liu, F., Liu, B., & Brusseau, M. L. (2018). Treatment of 1,4-dioxane and trichloroethene co-contamination by an activated binary persulfate-peroxide oxidation process. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH, 25(32), 32088-32095.
• Arthur, J. D., Mark, N. W., Taylor, S., Simunek, J., Brusseau, M. L., & Dontsova, K. M. (2017). Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils. JOURNAL OF CONTAMINANT HYDROLOGY, 199, 14-23.
• Danish, M., Gu, X., Lu, S., Brusseau, M. L., Ahmad, A., Naqvi, M., Farooq, U., Zaman, W. Q., Fu, X., & Miao, Z. (2017). An efficient catalytic degradation of trichloroethene in a percarbonate system catalyzed by ultra-fine heterogeneous zeolite supported zero valent iron-nickel bimetallic composite. APPLIED CATALYSIS A-GENERAL, 531, 177-186.
• Duncan, C. M., Mainhagu, J., Virgone, K., Ramirez, D. M., & Brusseau, M. L. (2017). Application of phytoscreening to three hazardous waste sites in Arizona. SCIENCE OF THE TOTAL ENVIRONMENT, 609, 951-955.
• Farooq, U., Danish, M., Lu, S., Brusseau, M. L., Naqvi, M., Fu, X., Zhang, X., Sui, Q., & Qiu, Z. (2017). Efficient transformation in characteristics of cations supported-reduced graphene oxide nanocomposites for the destruction of trichloroethane. APPLIED CATALYSIS A-GENERAL, 544, 10-20.
• Fu, X., Brusseau, M. L., Zang, X., Lu, S., Zhang, X., Farooq, U., Qiu, Z., & Sui, Q. (2017). Enhanced effect of HAH on citric acid-chelated Fe(II)-catalyzed percarbonate for trichloroethene degradation. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH, 24(31), 24318-24326.
• Fu, X., Gu, X., Lu, S., Sharma, V. K., Brusseau, M. L., Xue, Y., Danish, M., Fu, G. Y., Qiu, Z., & Sui, Q. (2017). Benzene oxidation by Fe(III)-activated percarbonate: matrix-constituent effects and degradation pathways. CHEMICAL ENGINEERING JOURNAL, 309, 22-29.
• Guo, Z., & Brusseau, M. L. (2017). Modified Well-Field Configurations for Improved Performance of Contaminant Elution and Tracer Tests. WATER AIR AND SOIL POLLUTION, 228(7).
• Guo, Z., & Brusseau, M. L. (2017). The impact of well-field configuration and permeability heterogeneity on contaminant mass removal and plume persistence. JOURNAL OF HAZARDOUS MATERIALS, 333, 109-115.
• Guo, Z., & Brusseau, M. L. (2017). The impact of well-field configuration on contaminant mass removal and plume persistence for homogeneous versus layered systems. HYDROLOGICAL PROCESSES, 31(26), 4748-4756.
• Liu, G., Zhong, H., Jiang, Y., Brusseau, M. L., Huang, J., Shi, L., Liu, Z., Liu, Y., & Zeng, G. (2017). Effect of low-concentration rhamnolipid biosurfactant on Pseudomonas aeruginosa transport in natural porous media. WATER RESOURCES RESEARCH, 53(1), 361-375.
• Lyu, Y., & Brusseau, M. L. (2017). Optimizing the Gas Absorption/Chemical Reaction Method for Measuring Air-Water Interfacial Area in Porous Media. WATER AIR AND SOIL POLLUTION, 228(12).
• Lyu, Y., Brusseau, M. L., El, O. A., Araujo, J. B., & Su, X. (2017). The Gas-Absorption/Chemical-Reaction Method for Measuring Air-Water Interfacial Area in Natural Porous Media. WATER RESOURCES RESEARCH, 53(11), 9519-9527.
• Mark, N., Arthur, J., Dontsova, K., Brusseau, M., Taylor, S., & Simunek, J. (2017). Column transport studies of 3-nitro-1,2,4-triazol-5-one (NTO) in soils. CHEMOSPHERE, 171, 427-434.
• Pu, M., Ma, Y., Wan, J., Wang, Y., Wang, J., & Brusseau, M. L. (2017). Activation performance and mechanism of a novel heterogeneous persulfate catalyst: metal-organic frameworkMIL-53(Fe) with Fe-II/Fe-III mixed-valence coordinatively unsaturated iron center. CATALYSIS SCIENCE & TECHNOLOGY, 7(5), 1129-1140.
• Rehman, Z. U., Khan, S., Brusseau, M. L., & Shah, M. T. (2017). Lead and cadmium contamination and exposure risk assessment via consumption of vegetables grown in agricultural soils of five-selected regions of Pakistan. CHEMOSPHERE, 168, 1589-1596.
• Yan, N. i., Li, M., Liu, Y., Liu, F., & Brusseau, M. L. (2017). Kinetic and Thermodynamic Studies of Chlorinated Organic Compound Degradation by Siderite-Activated Peroxide and Persulfate. WATER AIR AND SOIL POLLUTION, 228(12).
• Zhang, X., Gu, X., Lu, S., Brusseau, M. L., Xu, M., Fu, X., Qiu, Z., & Sui, Q. (2017). Application of ascorbic acid to enhance trichioroethene degradation by Fe(III)-activated calcium peroxide. CHEMICAL ENGINEERING JOURNAL, 325, 188-198.
• Zhong, H., Tian, Y., Yang, Q. i., Brusseau, M. L., Yang, L., & Zeng, G. (2017). Degradation of landfill leachate compounds by persulfate for groundwater remediation. CHEMICAL ENGINEERING JOURNAL, 307, 399-407.
• Lin, D., Jin, M., Brusseau, M. L., Liu, Y., & Zhang, D. (2016). Using tracer tests to estimate vertical recharge and evaluate influencing factors for irrigated agricultural systems. ENVIRONMENTAL EARTH SCIENCES, 75(22).
• Mainhagu, J., & Brusseau, M. L. (2016). Estimating initial contaminant mass. based on fitting mass-depletion functions to contaminant mass discharge data: Testing method efficacy with SVE operations data. JOURNAL OF CONTAMINANT HYDROLOGY, 192, 152-157.
• Mark, N., Arthur, J., Dontsova, K., Brusseau, M., & Taylor, S. (2016). Adsorption and attenuation behavior of 3-nitro-1,2,4-triazol-5-one (NTO) in eleven soils. Chemosphere, 144, 1249-55.
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  NTO (3-nitro-1,2,4-triazol-5-one) is one of the new explosive compounds used in insensitive munitions (IM) developed to replace traditional explosives, TNT and RDX. Data on NTO fate and transport is needed to determine its environmental behavior and potential for groundwater contamination. We conducted a series of kinetic and equilibrium batch experiments to characterize the fate of NTO in soils and the effect of soil geochemical properties on NTO-soil interactions. A set of experiments was also conducted using sterilized soils to evaluate the contribution of biodegradation to NTO attenuation. Measured pH values for NTO solutions decreased from 5.98 ± 0.13 to 3.50 ± 0.06 with increase in NTO concentration from 0.78 to 100 mg L(-1). Conversely, the pH of soil suspensions was not significantly affected by NTO in this concentration range. NTO experienced minimal adsorption, with measured adsorption coefficients being less than 1 cm(3) g(-1) for all studied soils. There was a highly significant inverse relationship between the measured NTO adsorption coefficients and soil pH (P = 0.00011), indicating the role of NTO and soil charge in adsorption processes. In kinetic experiments, 1st order transformation rate constant estimates ranged between 0.0004 h(-1) and 0.0142 h(-1) (equivalent to half-lives of 72 and 2 d, respectively), and correlated positively with organic carbon in the soil. Total attenuation of NTO was higher in untreated versus sterilized samples, suggesting that NTO was being biodegraded. The information presented herein can be used to help evaluate NTO potential for natural attenuation in soils.
• McDonald, K., Carroll, K. C., & Brusseau, M. L. (2016). Comparison of fluid-fluid interfacial areas measured with X-ray microtomography and interfacial partitioning tracer tests for the same samples. WATER RESOURCES RESEARCH, 52(7), 5393-5399.
• Rehman, Z. U., Khan, S., Qin, K., Brusseau, M. L., Shah, M. T., & Din, I. (2016). Quantification of inorganic arsenic exposure and cancer risk via consumption of vegetables in southern selected districts of Pakistan. SCIENCE OF THE TOTAL ENVIRONMENT, 550, 321-329.
• Xue, Y., Gu, X., Lu, S., Miao, Z., Brusseau, M. L., Xu, M., Fu, X., Zhang, X., Qiu, Z., & Sui, Q. (2016). The destruction of benzene by calcium peroxide activated with Fe(II) in water. CHEMICAL ENGINEERING JOURNAL, 302, 187-193.
• Yan, N. i., Liu, F., Chen, Y., & Brusseau, M. L. (2016). Influence of Groundwater Constituents on 1,4-Dioxane Degradation by a Binary Oxidant System. WATER AIR AND SOIL POLLUTION, 227(12).
• Zhang, X., Gu, X., Lu, S., Miao, Z., Xu, M., Fu, X., Danish, M., Brusseau, M. L., Qiu, Z., & Sui, Q. (2016). Enhanced degradation of trichloroethene by calcium peroxide activated with Fe(III) in the presence of citric acid. FRONTIERS OF ENVIRONMENTAL SCIENCE & ENGINEERING, 10(3), 502-512.
• Zhong, H., El, O. A., Lin, D., Wang, B., & Brusseau, M. L. (2016). The two-phase flow IPTT method for measurement of nonwetting-wetting liquid interfacial areas at higher nonwetting saturations in natural porous media. WATER RESOURCES RESEARCH, 52(7), 5506-5515.
• Zhong, H., Liu, G., Jiang, Y., Brusseau, M. L., Liu, Z., Liu, Y., & Zeng, G. (2016). Effect of low-concentration rhamnolipid on transport of Pseudomonas aeruginosa ATCC 9027 in an ideal porous medium with hydrophilic or hydrophobic surfaces. COLLOIDS AND SURFACES B-BIOINTERFACES, 139, 244-248.
• Zhong, H., Yang, X., Tan, F., Brusseau, M. L., Yang, L., Liu, Z., Zeng, G., & Yuan, X. (2016). Aggregate-based sub-CMC solubilization of n-alkanes by monorhamnolipid biosurfactant. NEW JOURNAL OF CHEMISTRY, 40(3), 2028-2035.
• Zhong, H., Zhang, H., Liu, Z., Yang, X., Brusseau, M. L., & Zeng, G. (2016). Sub-CMC solubilization of dodecane by rhamnolipid in saturated porous media. SCIENTIFIC REPORTS, 6.
• Araujo, J. B., Mainhagu, J., & Brusseau, M. L. (2015). Measuring air-water interfacial area for soils using the mass balance surfactant-tracer method. Chemosphere, 134, 199-202.
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  There are several methods for conducting interfacial partitioning tracer tests to measure air-water interfacial area in porous media. One such approach is the mass balance surfactant tracer method. An advantage of the mass-balance method compared to other tracer-based methods is that a single test can produce multiple interfacial area measurements over a wide range of water saturations. The mass-balance method has been used to date only for glass beads or treated quartz sand. The purpose of this research is to investigate the effectiveness and implementability of the mass-balance method for application to more complex porous media. The results indicate that interfacial areas measured with the mass-balance method are consistent with values obtained with the miscible-displacement method. This includes results for a soil, for which solid-phase adsorption was a significant component of total tracer retention.
• Brusseau, M. L., El Ouni, A., Araujo, J. B., & Zhong, H. (2015). Novel methods for measuring air-water interfacial area in unsaturated porous media. Chemosphere, 127, 208-13.
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  Interfacial partitioning tracer tests (IPTT) are used to measure air-water interfacial area for unsaturated porous media. The standard IPTT method involves conducting tests wherein an aqueous surfactant solution is introduced into a packed column under unsaturated flow conditions. Surfactant-induced drainage has been observed to occur for this method in some cases, which can complicate data analysis and impart uncertainty to the measured values. Two novel alternative approaches for conducting IPTTs are presented herein that are designed in part to prevent surfactant-induced drainage. The two methods are termed the dual-surfactant IPTT (IPTT-DS) and the residual-air IPTT (IPTT-RA). The two methods were used to measure air-water interfacial areas for two natural porous media. System monitoring during the tests revealed no measurable surfactant-induced drainage. The measured interfacial areas compared well to those obtained with the standard IPTT method conducted in such a manner that surfactant-induced drainage was prevented.
• Brusseau, M. L., Mainhagu, J., Morrison, C., & Carroll, K. C. (2015). The vapor-phase multi-stage CMD test for characterizing contaminant mass discharge associated with VOC sources in the vadose zone: Application to three sites in different lifecycle stages of SVE operations. Journal of contaminant hydrology, 179, 55-64.
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  Vapor-phase multi-stage contaminant mass discharge (CMD) tests were conducted at three field sites to measure mass discharge associated with contaminant sources located in the vadose zone. The three sites represent the three primary stages of the soil vapor extraction (SVE) operations lifecycle-pre/initial-SVE, mid-lifecycle, and near-closure. A CMD of 32g/d was obtained for a site at which soil vapor SVE has been in operation for approximately 6years, and for which mass removal is currently in the asymptotic stage. The contaminant removal behavior exhibited for the vapor extractions conducted at this site suggests that there is unlikely to be a significant mass of non-vapor-phase contaminant (e.g., DNAPL, sorbed phase) remaining in the advective domains, and that most remaining mass is likely located in poorly accessible domains. Given the conditions for this site, this remaining mass is hypothesized to be associated with the low-permeability (and higher water saturation) region in the vicinity of the saturated zone and capillary fringe. A CMD of 25g/d was obtained for a site wherein SVE has been in operation for several years but concentrations and mass-removal rates are still relatively high. A CMD of 270g/d was obtained for a site for which there were no prior SVE operations. The behavior exhibited for the vapor extractions conducted at this site suggest that non-vapor-phase contaminant mass (e.g., DNAPL) may be present in the advective domains. Hence, the asymptotic conditions observed for this site most likely derive from a combination of rate-limited mass transfer from DNAPL (and sorbed) phases present in the advective domain as well as mass residing in lower-permeability ("non-advective") regions. The CMD values obtained from the tests were used in conjunction with a recently developed vapor-discharge tool to evaluate the impact of the measured CMDs on groundwater quality.
• Carroll, K., McDonald, K., Marble, J., Russo, A., & Brusseau, M. L. (2015). The impact of transitions between two-fluid and three-fluid phases on fluid configuration and fluid-fluid interfacial area in porous media. Water Resources Reserach, 51, 7189–7201. doi:doi:10.1002/2015WR017490.
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  Multiphase-fluid distribution and flow is inherent in numerous areas of hydrology. Yet porescalecharacterization of transitions between two and three immiscible fluids is limited. The objective of thisstudy was to examine the impact of such transitions on the pore-scale configuration of organic liquid in amultifluid system comprising natural porous media. Three-dimensional images of an organic liquid(trichloroethene) in two-phase (organic-liquid/water) and three-phase (air/organic-liquid/water) systemswere obtained using X-ray microtomography before and after drainage and imbibition. Upon transitionfrom a two-phase to a three-phase system, a significant portion of the organic liquid (intermediate wettingfluid) was observed to exist as lenses and films in contact with air (nonwetting fluid). In these cases, the airwas either encased by or contiguous to the organic liquid. The presence of air resulted in an increase in thesurface-area-to-volume ratios for the organic-liquid blobs. Upon imbibition, the air was displaced downgradient,and concomitantly, the morphology of the organic-liquid blobs no longer in contact with air revertedto that characteristic of a two-phase distribution (i.e., more spherical blobs and ganglia). This change inmorphology resulted in a reduction in the surface-area-to-volume ratio. These results illustrate the impactof transitions between two-phase and three-phase conditions on fluid configuration, and they demonstratethe malleable nature of fluid configuration under dynamic, multiphase-flow conditions. The results haveimplications for characterizing and modeling pore-scale flow and mass transfer processes.
• Izady, A., Brusseau, M. L., & coauthors, 6. o. (2015). Groundwater conceptualization and modeling using distributed SWATbased recharge for the semi-arid agricultural Neishaboor plain, Iran. Hydrogeology Journal, 23, 23: 47–68. doi:DOI 10.1007/s10040-014-1219-9
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  Increased irrigation in the Neishaboor watershed,Iran, during the last few decades has caused seriousgroundwater depletion, making the development of comprehensivemitigation strategies and tools increasinglyimportant. In this study, SWAT and MODFLOW wereemployed to integratively simulate surface-water andgroundwater flows. SWAT and MODFLOW were iterativelyexecuted to compute spatial and temporal distributionsof hydrologic components. The combined SWATMODFLOWmodel was calibrated (2000–2010) andvalidated (2010–2012) based on streamflow, wheat yield,groundwater extraction, and groundwater-level data. Thismulti-criteria calibration procedure provided greater confidencefor the partitioning of water between soil storage,actual evapotranspiration, and aquifer recharge. TheSWAT model provided satisfactory predictions of thehydrologic budget for the watershed outlet. It alsoprovided good predictions of irrigated wheat yield andgroundwater extraction.
• Mainhagu, J., Morrison, C., & Brusseau, M. L. (2015). Using vapor phase tomography to measure the spatial distribution of vapor concentrations and flux for vadose-zone VOC sources. Journal of contaminant hydrology, 177-178, 54-63.
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  A test was conducted at a chlorinated-solvent contaminated site in Tucson, AZ, to evaluate the effectiveness of vapor-phase tomography (VPT) for characterizing the distribution of volatile organic contaminants (VOC) in the vadose zone. A soil vapor extraction (SVE) system has been in operation at the site since 2007. Vapor concentration and vacuum pressure were measured at four different depths in each of the four monitoring wells surrounding the extraction well. The test provided a 3D characterization of local vapor concentrations under induced-gradient conditions. Permeability data obtained from analysis of borehole logs were used along with pressure and the vapor-concentration data to determine VOC mass flux within the test domain. A region of higher mass flux was identified in the deepest interval of the S-SW section of the domain, indicating the possible location of a zone with greater contaminant mass. These results are consistent with the TCE-concentration distribution obtained from sediment coring conducted at the site. In contrast, the results of a standard soil gas survey did not indicate the presence of a zone with greater contaminant mass. These results indicate that the VPT test provided a robust characterization of VOC concentration and flux distribution at the site.
• Miao, Z., Gu, X., Lu, S., Brusseau, M. L., Yan, N., Qiu, Z., & Sui, Q. (2015). Enhancement effects of reducing agents on the degradation of tetrachloroethene in the Fe(II)/Fe(III) catalyzed percarbonate system. Journal of hazardous materials, 300, 530-7.
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  In this study, the effects of reducing agents on the degradation of tetrachloroethene (PCE) were investigated in the Fe(II)/Fe(III) catalyzed sodium percarbonate (SPC) system. The addition of reducing agents, including hydroxylamine hydrochloride, sodium sulfite, ascorbic acid and sodium ascorbate, accelerated the Fe(III)/Fe(II) redox cycle, leading to a relatively steady Fe(II) concentration and higher production of free radicals. This, in turn, resulted in enhanced PCE oxidation by SPC, with almost complete PCE removal obtained for appropriate Fe and SPC concentrations. The chemical probe tests, using nitrobenzene and carbon tetrachloride, demonstrated that HO was the predominant radical in the system and that O2(-) played a minor role, which was further confirmed by the results of electron spin resonance measurements. PCE degradation decreased significantly with the addition of isopropanol, a HO scavenger, supporting the hypothesis that HO was primarily responsible for PCE degradation. It is noteworthy that Cl(-) release was slightly delayed in the first 20min, indicating that intermediate products were produced. However, these intermediates were further degraded, resulting in the complete conversion of PCE to CO2. In conclusion, the use of reducing agents to enhance Fe(II)/Fe(III) catalyzed SPC oxidation appears to be a promising approach for the rapid degradation of organic contaminants in groundwater.
• Miao, Z., Gu, X., Lu, S., Brusseau, M. L., Zhang, X., Fu, X., Danish, M., Qiu, Z., & Sui, Q. (2015). Enhancement effects of chelating agents on the degradation of tetrachloroethene in Fe(III) catalyzed percarbonate system. Chemical engineering journal (Lausanne, Switzerland : 1996), 281, 286-294.
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  The performance of Fe(III)-based catalyzed sodium percarbonate (SPC) for stimulating the oxidation of tetrachloroethene (PCE) for groundwater remediation applications was investigated. The chelating agents citric acid monohydrate (CIT), oxalic acid (OA), and Glutamic acid (Glu) significantly enhanced the degradation of PCE. Conversely, ethylenediaminetetraacetic acid (EDTA) had a negative impact on PCE degradation, which may due to its strong Fe chelation and HO(•) scavenging abilities. However, excessive SPC or chelating agent will retard PCE degradation. In addition, investigations using free radical probe compounds and radical scavengers revealed that PCE was primarily degraded by HO(•) radical oxidation in both the chelated and non-chelated systems, while O2 (•-) also participated in the non-chelated system and the OA and Glu modified systems. According to the electron paramagnetic resonance (EPR) studies, the presence of HO(•) in the Fe(III)/SPC system was maintained much longer than that in the Fe(II)/SPC system. The results indicated that the addition of CIT, OA or Glu indeed enhanced the generation of HO(•) in the first 10 min and promoted degradation efficiency by increasing the amount of Fe(III) and maintaining the concentration of HO(•) radicals in solution. In conclusion, chelated Fe(III)-based catalyzed SPC oxidation is a promising method for the remediation of PCE-contaminated groundwater.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J., Maier, R. M., & Gandolfi, A. J. (2015). Building a co-created citizen science program with gardeners neighboring a superfund site: The Gardenroots case study. International public health journal, 7(1).
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  A research project that is only expert-driven may ignore the role of local knowledge in research, give low priority to the development of a comprehensive communication strategy to engage the community, and may not deliver the results of the study to the community in an effective way.
• Yan, N., Liu, F., Xue, Q., Brusseau, M. L., Liu, Y., & Wang, J. (2015). Degradation of trichloroethene by siderite-catalyzed hydrogen peroxide and persulfate: Investigation of reaction mechanisms and degradation products. Chemical engineering journal (Lausanne, Switzerland : 1996), 274, 61-68.
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  A binary catalytic system, siderite-catalyzed hydrogen peroxide (H2O2) coupled with persulfate (S2O8 (2-)), was investigated for the remediation of trichloroethene (TCE) contamination. Batch experiments were conducted to investigate reaction mechanisms, oxidant decomposition rates, and degradation products. By using high performance liquid chromatography (HPLC) coupled with electron paramagnetic resonance (EPR), we identified four radicals (hydroxyl (HO·), sulfate (SO4 (-)·), hydroperoxyl (HO2·), and superoxide (O2 (-)·)) in the siderite-catalyzed H2O2-S2O8 (2-) system. In the absence of S2O8 (2-) (i.e., siderite-catalyzed H2O2), a majority of H2O2 was decomposed in the first hour of the experiment, resulting in the waste of HO·. The addition of S2O8 (2-) moderated the H2O2 decomposition rate, producing a more sustainable release of hydroxyl radicals that improved the treatment efficiency. Furthermore, the heat released by H2O2 decomposition accelerated the activation of S2O8 (2-), and the resultant SO4 (-)· was the primary oxidative agent during the first two hours of the reaction. Dichloroacetic acid was firstly detected by ion chromatography (IC). The results of this study indicate a new insight to the reaction mechanism for the catalytic binary H2O2-S2O8 (2-) oxidant system, and the delineation of radicals and the discovery of the chlorinated byproduct provide useful information for efficient treatment of chlorinated-solvent contamination in groundwater.
• Zhong, H., Brusseau, M. L., & coauthors, 7. o. (2015). Aggregate-based sub-CMC solubilization of hexadecane by surfactants. RSC Advances, 5, 78142–78149. doi:DOI: 10.1039/c5ra12388g
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  Solubilizaiton of hexadecane by two surfactants, SDBS and Triton X-100, at concentrations near the criticalmicelle concentration (CMC) and the related aggregation behavior was investigated in this study.Solubilization was observed at surfactant concentrations lower than CMC, and the apparent solubility ofhexadecane increased linearly with surfactant concentration for both surfactants. The capacity of SDBSto solubilize hexadecane is stronger at concentrations below CMC than above CMC. In contrast, TritonX-100 shows no difference. The results of dynamic light scattering (DLS) and cryogenic TEM analysisshow aggregate formation at surfactant concentrations lower than CMC. DLS-based size of theaggregates (d) decreases with increasing surfactant concentration. The zeta potential of the SDBSaggregates decreases with increasing SDBS concentration, whereas it increases for Triton X-100. Thesurface excess (G) of SDBS calculated based on hexadecane solubility and aggregate size data increasesrapidly with increasing bulk concentration, and then asymptotically approaches the maximum surfaceexcess (Gmax). Conversely, there is only a minor increase in G for Triton X-100. Comparison of G and dindicates that an excess of surfactant molecules at the aggregate surface has a great impact on surfacecurvature. The results of this study demonstrate the formation of aggregates at surfactant concentrationsbelow CMC for hexadecane solubilization, and indicate the potential of employing a low-concentrationstrategy for surfactant applications such as remediation of HOC contaminated sites.
• Zhong, H., Brusseau, M. L., Wang, Y., Yan, N., Quig, L., & Johnson, G. R. (2015). In-situ activation of persulfate by iron filings and degradation of 1,4-dioxane. Water research, 83, 104-11.
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  Activation of persulfate by iron filings and subsequent degradation of 1,4-dioxane (dioxane) was studied in both batch-reactor and column systems to evaluate the potential of a persulfate-enhanced permeable reactive barrier (PRB) system for combined oxidative-reductive removal of organic contaminants from groundwater. In batch experiments, decomposition of persulfate to sulfate and degradation of dioxane both occurred rapidly in the presence of iron filings. Conversely, dioxane degradation by persulfate was considerably slower in the absence of iron filings. For the column experiments, decomposition and retardation of persulfate was observed for transport in the columns packed with iron filings, whereas no decomposition or retardation was observed for transport in columns packed with a reference quartz sand. Both sulfate production and dioxane degradation were observed for the iron-filings columns, but not for the sand column. The pH of the column effluent increased temporarily before persulfate breakthrough, and significant increases in both ferrous and ferric iron coincided with persulfate breakthrough. Multiple species of free radicals were produced from persulfate activation as determined by electron paramagnetic resonance (EPR) spectroscopy. The impact of the oxidation process on solution composition and iron-filings surface chemistry was examined using ICP-MS, SEM-EDS, and XRD analyses. A two-stage reaction mechanism is proposed to describe the oxidation process, consisting of a first stage of rapid, solution-based, radical-driven decomposition of dioxane and a second stage governed by rate-limited surface reaction. The results of this study show successful persulfate activation using iron filings, and the potential to apply an enhanced PRB method for improving in-situ removal of organic contaminants from groundwater.
• Artiola, J. F., Brusseau, M. L., Maier, R. M., Ramirez-Andreotta, M., & Gandolfi, J. (2014). Building a Co-CreatedCitizen Science Program with Gardeners Neighboring a Superfund Site: The Gardenroots Case Study. International Public Health Journal, 6(3).
• Brusseau, M. L., & Guo, Z. (2014). Assessing contaminant-removal conditions and plume persistence through analysis of data from long-term pump-and-treat operations. JOURNAL OF CONTAMINANT HYDROLOGY, 164, 16-24.
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  Historical groundwater-withdrawal and contaminant-concentration data collected from long-term pump-and-treat operations were analyzed and used to examine contaminant mass discharge (CMD) and mass-removal behavior for multiple sites. Differences in behavior were observed, and these differences were consistent with the nature of contaminant distributions and subsurface properties of the sites. For example, while CMD exhibited a relatively rapid decline during the initial stage of operation for all three sites, the rate of decline varied. The greatest rate was observed for the PGN site, whereas the lowest rate was observed for the MOT site. In addition, the MOT site exhibited the lowest relative reduction in CMD. These results are consistent with the actuality that the MOT site likely contains the greatest proportion of poorly accessible contaminant mass, given that it comprises a combined alluvium and fractured-bedrock system in which solvent and dissolved mass are present directly in the bedrock. The relative contributions of the source zones versus the plumes to total CMD were determined. Constrained contaminant mass removal was observed to influence the plumes for all three sites, and was attributed to a combination of uncontrolled (or imperfectly controlled) sources, back diffusion, and well-field hydraulics. The results presented herein illustrate that detailed analysis of operational pump-and-treat data can be a cost-effective method for providing value-added characterization of contaminated sites. (C) 2014 Elsevier B.V. All rights reserved.
• Izady, A., Davary, K., Alizadeh, A., Ziaei, A. N., Alipoor, A., Joodavi, A., & Brusseau, M. L. (2014). A framework toward developing a groundwater conceptual model. ARABIAN JOURNAL OF GEOSCIENCES, 7(9), 3611-3631.
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  Developing an accurate conceptual model is the most important step in the process of a groundwater numerical modeling. Disorganized and limited available data and information, especially in the developing countries, make the preparation of the conceptual model difficult and sometimes cumbersome. In this research, an integrative and comprehensive method is proposed to develop groundwater conceptual model for an unconfined aquifer. The proposed method consists of six steps. A preliminary step (step 0) is aimed at collecting all the available data and information. The output of the first step as "controlling observations" is conceptual model version 00. This step should be rigorously checked due to its critical role in the controlling of final conceptual model. Step 2 determines the aquifer geometry. The output of this step is conceptual model version 01. Step 3 is responsible to determine hydrodynamic properties and its output develops conceptual model version 02. Step 4 evaluates the surface and subsurface interactions and lateral in/out groundwater flows. The output of this step is conceptual model version 03. Step 5 is to integrate the results from other steps and to deliver the final conceptual model version. The accuracy level of the conceptual model and the annual groundwater balance is also determined at this step. The presented groundwater conceptual model procedure was implemented for the Neishaboor plain, Iran. Results showed its usefulness and practicality in developing the conceptual model for the study area.
• Mainhagu, J., Morrison, C., Truex, M., Oostrom, M., & Brusseau, M. L. (2014). Measuring spatial variability of vapor flux to characterize vadose-zone VOC sources: Flow-cell experiments. JOURNAL OF CONTAMINANT HYDROLOGY, 167, 32-43.
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  A method termed vapor-phase tomography has recently been proposed to characterize the distribution of volatile organic contaminant mass in vadose-zone source areas, and to measure associated three-dimensional distributions of local contaminant mass discharge. The method is based on measuring the spatial variability of vapor flux, and thus inherent to its effectiveness is the premise that the magnitudes and temporal variability of vapor concentrations measured at different monitoring points within the interrogated area will be a function of the geospatial positions of the points relative to the source location. A series of flow-cell experiments was conducted to evaluate this premise. A well-defined source zone was created by injection and extraction of a non-reactive gas (SF6). Spatial and temporal concentration distributions obtained from the tests were compared to simulations produced with a mathematical model describing advective and diffusive transport. Tests were conducted to characterize both areal and vertical components of the application. Decreases in concentration over time were observed for monitoring points located on the opposite side of the source zone from the local-extraction point, whereas increases were observed for monitoring points located between the local-extraction point and the source zone. The results illustrate that comparison of temporal concentration profiles obtained at various monitoring points gives a general indication of the source location with respect to the extraction and monitoring points. (C) 2014 Elsevier B.V. All rights reserved.
• Marble, J. C., Brusseau, M. L., Carroll, K. C., Plaschke, M., Fuhrig, L., & Brinker, F. (2014). Application of a Persistent Dissolved-Phase Reactive Treatment Zone for Mitigation of Mass Discharge from Sources Located in Lower-Permeability Sediments. WATER AIR AND SOIL POLLUTION, 225(11).
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  The purpose of this study is to examine the development and effectiveness of a persistent dissolved-phase treatment zone, created by injecting potassium permanganate solution, for mitigating discharge of contaminant from a source zone located in a relatively deep, low-permeability formation. A localized 1,1-dichloroethene (DCE) source zone comprising dissolved-and sorbed-phase mass is present in lower-permeability strata adjacent to sand/gravel units in a section of the Tucson International Airport Area (TIAA) Superfund Site. The results of bench-scale studies conducted using core material collected from boreholes drilled at the site indicated that natural oxidant demand was low, which would promote permanganate persistence. The reactive zone was created by injecting a permanganate solution into multiple wells screened across the interface between the lower-permeability and higher-permeability units. The site has been monitored for 9 years to characterize the spatial distribution of DCE and permanganate. Permanganate continues to persist at the site, and a substantial and sustained decrease in DCE concentrations in groundwater has occurred after the permanganate injection. These results demonstrate successful creation of a long-term, dissolved-phase reactive treatment zone that reduced mass discharge from the source. This project illustrates the application of in situ chemical oxidation as a persistent dissolved-phase reactive treatment system for lower-permeability source zones, which appears to effectively mitigate persistent mass discharge into groundwater.
• Matthieu, D. E., Brusseau, M. L., Guo, Z., Plaschke, M., Carroll, K. C., & Brinker, F. (2014). Persistence of a Groundwater Contaminant Plume after Hydraulic Source Containment at a Chlorinated-Solvent Contaminated Site. GROUND WATER MONITORING AND REMEDIATION, 34(4), 23-32.
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  The objective of this study was to characterize the behavior of a groundwater contaminant (trichloroethene, TCE) plume after implementation of a source-containment operation at a site in Arizona. The plume resides in a quasi-three-layer system comprising a sand/gravel unit bounded on the top and bottom by relatively thick silty clayey layers. The system was monitored for 60 months beginning at start-up in 2007 to measure the change in contaminant concentrations within the plume, the change in plume area, the mass of the contaminant removed, and the integrated contaminant mass discharge (CMD). The concentrations of TCE in groundwater pumped from the plume extraction wells have declined significantly over the course of operation, as have concentrations for groundwater sampled from 40 monitoring wells located within the plume. The total CMD associated with operation of the plume extraction wells peaked at 0.23 kg/d, decreased significantly within 1 year, and thereafter began an asymptotic decline to a current value of approximately 0.03 kg/d. Despite an 87% reduction in contaminant mass and a comparable 87% reduction in CMD for the plume, the spatial area encompassed by the plume has decreased by only approximately 50%. This is much less than would be anticipated based on ideal flushing and mass-removal behavior. Simulations produced with a simplified three-dimensional (3D) numerical model matched reasonably well to the measured data. The results of the study suggest that permeability heterogeneity, back diffusion, hydraulic factors associated with the specific well field system, and residual discharge from the source zone are all contributing to the observed persistence of the plume, as well as the asymptotic behavior currently observed for mass removal and for the reduction in CMD.
• Miao, Z., Carreon-Diazconti, C., Carroll, K. C., & Brusseau, M. L. (2014). The impact of biostimulation on the fate of sulfate and associated sulfur dynamics in groundwater. JOURNAL OF CONTAMINANT HYDROLOGY, 164, 240-250.
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  The impact of electron-donor addition on sulfur dynamics for a groundwater system with low levels of metal contaminants was evaluated with a pilot-scale biostimulation test conducted at a former uranium mining site. Geochemical and stable-isotope data collected before, during, and after the test were analyzed to evaluate the sustainability of sulfate reducing conditions induced by the test, the fate of hydrogen sulfide, and the impact on aqueous geochemical conditions. The results of site characterization activities conducted prior to the test indicated the absence of measurable bacterial sulfate reduction. The injection of an electron donor (ethanol) induced bacterial sulfate reduction, as confirmed by an exponential decrease of sulfate concentration in concert with changes in oxidation-reduction potential, redox species, alkalinity, production of hydrogen sulfide, and fractionation of delta S-34-sulfate. High, stoichiometrically-equivalent hydrogen sulfide concentrations were not observed until several months after the start of the test. It is hypothesized that hydrogen sulfide produced from sulfate reduction was initially sequestered in the form of iron sulfides until the exhaustion of readily reducible iron oxides within the sediment. The fractionation of delta S-34 for sulfate was atypical, wherein the enrichment declined in the latter half of the experiment. It was conjectured that mixing effects associated with the release of sulfate from sulfate minerals associated with the sediments, along with possible sulfide re-oxidation contributed to this behavior. The results of this study illustrate the biogeochemical complexity that is associated with in-situ biostimulation processes involving bacterial sulfate reduction. (C) 2014 Elsevier B.V. All rights reserved.
• Monger, G. R., Duncan, C. M., & Brusseau, M. L. (2014). Using a Gas-Phase Tracer Test to Characterize the Impact of Landfill Gas Generation on Advective-Dispersive Transport of VOCs in the Vadose Zone. WATER AIR AND SOIL POLLUTION, 225(12).
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  A gas-phase tracer test (GTT) was conducted at a landfill in Tucson, AZ, to help elucidate the impact of landfill gas generation on the transport and fate of chlorinated aliphatic volatile organic contaminants (VOCs). Sulfur hexafluoride (SF6) was used as the nonreactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well and analyzed for SF6, CH4, CO2, and VOCs. The travel times determined for SF6 from the tracer test are approximately two to ten times smaller than estimated travel times that incorporate transport by only gas-phase diffusion. In addition, significant concentrations of CH4 and CO2 were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF6 are caused by advective transport associated with landfill gas generation. The rates of transport varied vertically, which is attributed to multiple factors including spatial variability of water content, refuse mass, refuse permeability, and gas generation.
• Musielak, M., Brusseau, M. L., Marcoux, M., Morrison, C., & Quintard, M. (2014). Determination of Chlorinated Solvent Sorption by Porous Material-Application to Trichloroethene Vapor on Cement Mortar. TRANSPORT IN POROUS MEDIA, 104(1), 77-90.
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  Experiments have been performed to investigate the sorption of trichloroethene (TCE) vapor by concrete material or, more specifically, the cement mortar component. Gas-flow experiments were conducted using columns packed with small pieces of cement mortar obtained from the grinding of typical concrete material. Transport and retardation of TCE at high vapor concentrations (500 mg L was compared to that of a non-reactive gas tracer (Sulfur Hexafluoride, SF. The results show a large magnitude of retardation (retardation factor 23) and sorption (sorption coefficient 10.6 cm g for TCE, compared to negligible sorption for SF. This magnitude of sorption obtained with pollutant vapor is much bigger than the one obtained for aqueous-flow experiments conducted for water-saturated systems. The considerable sorption exhibited for TCE under vapor-flow conditions is attributed to some combination of accumulation at the air-water interface and vapor-phase adsorption, both of which are anticipated to be significant for this system given the large surface area associated with the cement mortar. Transport of both SF and TCE was simulated successfully with a two-region physical non-equilibrium model, consistent with the dual-medium structure of the crushed cement mortar. This work emphasizes the importance of taking into account sorption phenomena when modeling transport of volatile organic compounds through concrete material, especially in regard to assessing vapor intrusion.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J. F., Maier, R. M., & Gandolfi, A. J. (2014). Environmental Research Translation: Enhancing interactions with communities at contaminated sites. Science of the Total Environment, 651-664.
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  The characterization and remediation of contaminated sites are complex endeavors fraught with numerous challenges. One particular challenge that is receiving increased attention is the development and encouragement of full participation by communities and community members affected by a given site in all facets of decision-making. Many disciplines have been grappling with the challenges associated with environmental and risk communication, public participation in environmental data generation, and decision-making and increasing community capacity. The concepts and methods developed by these disciplines are reviewed, with a focus on their relevance to the specific dynamics associated with environmental contamination sites. The contributions of these disciplines are then synthesized and integrated to help develop Environmental Research Translation (ERT), a proposed framework for environmental scientists to promote interaction and communication among involved parties at contaminated sites. This holistic approach is rooted in public participation approaches to science, which includes: a transdisciplinary team, effective collaboration, information transfer, public participation in environmental projects, and a cultural model of risk communication. Although there are challenges associated with the implementation of ERT, it is anticipated that application of this proposed translational science method could promote more robust community participation at contaminated sites. (C) 2014 Elsevier B.V. All rights reserved.
• Ramirez-Andreotta, M., Brusseau, M. L., Artiola, J., Maier, R., & Gandolfi, J. (2014). Building a Co-Created Citizen Science Program with Gardeners Neighboring a Superfund Site: The Gardenroots Case Study. International Journal of Public Health, 15.
• Schnaar, G., & Brusseau, M. L. (2014). Nonideal Transport of Contaminants in Heterogeneous Porous Media: 11. Testing the Experiment Condition Dependency of the Continuous Distribution Rate Model for Sorption-Desorption. WATER AIR AND SOIL POLLUTION, 225(11).
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  A series of miscible-displacement experiments was conducted to examine the impact of experiment conditions (detection limit, input pulse size, input concentration, pore-water velocity, contact time) on the performance of a mathematical solute transport model incorporating nonlinear, rate-limited sorption/desorption described by a continuous distribution reaction function. Effluent solute concentrations were monitored over a range of approximately seven orders of magnitude, allowing characterization of asymptotic tailing phenomenon. The model successfully simulated the extensive elution tailing observed for the measured data. Values for the mean desorption rate coefficient (ln k(2)) and the variance of ln k(2) were obtained through calibration of the model to measured data. Similar parameter values were obtained for experiments with different input pulse size, input concentration, pore-water velocity, and contact time. This suggests that the model provided a robust representation of sorption-desorption for this system tested. The impact of analytical detection limit was examined by calibrating the model to subsets of the breakthrough curves wherein the extent of the elution tail was artificially reduced to mimic a poorer detection limit. The parameters varied as a function of the extent of elution tail used for the calibrations, indicating the importance of measuring as full an extent of the tail as possible.
• Akyol, N. H., Lee, A. R., & Brusseau, M. L. (2013). Impact of enhanced-flushing reagents and organic liquid distribution on mass removal and mass discharge reduction. Water, Air, and Soil Pollution, 224(10).
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  Abstract: A series of column and flow cell experiments were conducted to investigate the impact of nonuniform organic liquid distribution on the relationship between reductions in contaminant mass discharge and reductions in source zone mass under conditions of enhancedsolubilization flushing. Trichloroethene was used as the model organic liquid, and sodium dodecyl sulfate and ethanol were used as representative enhanced-flushing reagents. The results were compared to those of waterflood control experiments. Concentrations of trichloroethene in the effluent exhibited a multi-step behavior with time, wherein multiple secondary periods of quasi steady state were observed. This nonideal behavior was observed for both the waterflood and enhanced-flushing experiments. For all flow cell experiments, the later stage of mass removal was controlled by the more poorly accessible mass associated with higher-saturation zones. The profiles relating reductions in contaminant mass discharge and reductions in mass exhibited a generally similar behavior for both the waterflood and enhanced-flushing experiments. This indicates that while the rates and magnitudes of mass removal are altered by the presence of a solubilization reagent solution, the fundamental mass removal process is not. The profiles obtained for the flow cell systems differed from those obtained for the column systems, highlighting the impact of source zone heterogeneity on mass removal behavior. © 2013 Springer Science+Business Media Dordrecht.
• Brusseau, M. L. (2013). A Framework Toward Developing a Groundwater Conceptual Model. Arabian Journal of Geosciences, DOI 10.1007/s12517-013-0971-9.
• Brusseau, M. L. (2013). Characterization and Quantification of Groundwater Sulfate Sources at a Mining Site in an Arid Climate: The Monument Valley Site in Arizona U.S.A.. J. Hydrology, 504, 207-215.
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  Miao, Z., K.C. Carroll, and M.L. Brusseau
• Brusseau, M. L. (2013). Characterization and Remediation of Chlorinated Volatile Organic Contaminants in the Vadose Zone. Vadose Zone Journal.
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  Brusseau, M.L., Carroll, K.C., Truex, M.J., and Becker, D.J.
• Brusseau, M. L. (2013). Characterization of Persistent Volatile Contaminant Sources in the Vadoze Zone. Ground Water Monitoring and Remediation, 33, 68-84.
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  Carroll, K.C., M.J. Truex, M.L. Brusseau, K.R. Parker, R.M. Mackley and V.J. Rohay
• Brusseau, M. L. (2013). Impact of enhanced-flushing reagents and organic-liquid distribution on mass removal and mass-discharge reduction.. Water, Air, Soil Pollution, 224, article 1731.
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  Akyol, N.H., A. Russo Lee, and M.L. Brusseau.
• Brusseau, M. L. (2013). Use of Historical Pump-and-Treat Data to Enhance Site Characterization and Remediation Performance Assessment.. Water Air Soil Pollution, 224, article 1741.
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  Brusseau, ML
• Brusseau, M. L. (2013). Use of historical pump-and-treat data to enhance site characterization and remediation performance assessment. Water, Air, and Soil Pollution, 224(10).
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  Abstract: Groundwater withdrawal and contaminant concentration data are routinely collected for pumpand-treat operations conducted at hazardous waste sites. These data sets can be mined to produce a wealth of information to support enhanced site characterization, optimization of remedial system operations, and improved decision making regarding long-term site management and closure. Methods that may be used to analyze and interpret pump-and-treat data to produce such assessments are presented, along with a brief illustration of their application to a site. The results presented herein illustrate that comprehensive analysis of pump-and-treat data is a powerful, cost-effective method for providing higher-resolution, value-added characterization of contaminated sites. © Springer Science+Business Media Dordrecht 2013.
• Brusseau, M. L., & Narter, M. (2013). Assessing the Impact of Chlorinated-Solvent Sites on Metropolitan Groundwater Resources. Ground water.
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  Chlorinated-solvent compounds are among the most common groundwater contaminants in the United States. A majority of the many sites contaminated by chlorinated-solvent compounds are located in metropolitan areas, and most such areas have one or more chlorinated-solvent contaminated sites. Thus, contamination of groundwater by chlorinated-solvent compounds may pose a potential risk to the sustainability of potable water supplies for many metropolitan areas. The impact of chlorinated-solvent sites on metropolitan water resources was assessed for Tucson, Arizona, by comparing the aggregate volume of extracted groundwater for all pump-and-treat systems associated with contaminated sites in the region to the total regional groundwater withdrawal. The analysis revealed that the aggregate volume of groundwater withdrawn for the pump-and-treat systems operating in Tucson, all of which are located at chlorinated-solvent contaminated sites, was 20% of the total groundwater withdrawal in the city for the study period. The treated groundwater was used primarily for direct delivery to local water supply systems or for reinjection as part of the pump-and-treat system. The volume of the treated groundwater used for potable water represented approximately 13% of the total potable water supply sourced from groundwater, and approximately 6% of the total potable water supply. This case study illustrates the significant impact chlorinated-solvent contaminated sites can have on groundwater resources and regional potable water supplies.
• Brusseau, M. L., & Narter, M. (2013). Assessing the impact of chlorinated-solvent sites on metropolitan groundwater resources. Groundwater, 51(6), 828-832.
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  Abstract: Chlorinated-solvent compounds are among the most common groundwater contaminants in the United States. A majority of the many sites contaminated by chlorinated-solvent compounds are located in metropolitan areas, and most such areas have one or more chlorinated-solvent contaminated sites. Thus, contamination of groundwater by chlorinated-solvent compounds may pose a potential risk to the sustainability of potable water supplies for many metropolitan areas. The impact of chlorinated-solvent sites on metropolitan water resources was assessed for Tucson, Arizona, by comparing the aggregate volume of extracted groundwater for all pump-and-treat systems associated with contaminated sites in the region to the total regional groundwater withdrawal. The analysis revealed that the aggregate volume of groundwater withdrawn for the pump-and-treat systems operating in Tucson, all of which are located at chlorinated-solvent contaminated sites, was 20% of the total groundwater withdrawal in the city for the study period. The treated groundwater was used primarily for direct delivery to local water supply systems or for reinjection as part of the pump-and-treat system. The volume of the treated groundwater used for potable water represented approximately 13% of the total potable water supply sourced from groundwater, and approximately 6% of the total potable water supply. This case study illustrates the significant impact chlorinated-solvent contaminated sites can have on groundwater resources and regional potable water supplies. © 2013, National Ground Water Association.
• Brusseau, M. L., Carroll, K. C., Truex, M. J., & Becker, D. J. (2013). Characterization and remediation of chlorinated volatile organic contaminants in the vadose zone. Vadose Zone Journal, 12(4).
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  Abstract: Contamination of vadose-zone systems by chlorinated solvents is widespread and poses significant potential risk to human health through impacts on groundwater quality and vapor intrusion. Soil vapor extraction (SVE) is the presumptive remedy for such contamination and has been used successfully for innumerable sites; however, SVE operations typically exhibit reduced mass-removal effectiveness at some point due to the impact of poorly accessible contaminant mass and associated mass-transfer limitations. Assessment of SVE performance and closure is currently based on characterizing contaminant mass discharge associated with the vadose-zone source and its impact on groundwater or vapor intrusion. These issues are addressed in this overview, with a focus on summarizing recent advances in our understanding of the transport, characterization, and remediation of chlorinated solvents in the vadose zone. The evolution of contaminant distribution with time and the associated impacts on remediation efficiency are discussed, as is potential impact of persistent sources on groundwater quality and vapor intrusion. In addition, alternative methods for site characterization and remediation are addressed. © Soil Science Society of America, All rights reserved.
• Brusseau, M. L., III, D. M., Carroll, K. C., Mainhagu, J., Morrison, C., McMillan, A., Russo, A., & Plaschke, M. (2013). Characterizing long-term contaminant mass discharge and the relationship between reductions in discharge and reductions in mass for DNAPL source areas. Journal of Contaminant Hydrology, 149, 1-12.
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  PMID: 23528743;PMCID: PMC3875322;Abstract: The objective of this study was to characterize the temporal behavior of contaminant mass discharge, and the relationship between reductions in contaminant mass discharge and reductions in contaminant mass, for a very heterogeneous, highly contaminated source-zone field site. Trichloroethene is the primary contaminant of concern, and several lines of evidence indicate the presence of organic liquid in the subsurface. The site is undergoing groundwater extraction for source control, and contaminant mass discharge has been monitored since system startup. The results show a significant reduction in contaminant mass discharge with time, decreasing from approximately 1 to 0.15 kg/d over five years. Two methods were used to estimate the mass of contaminant present in the source area at the initiation of the remediation project. One was based on a comparison of two sets of core data, collected 3.5 years apart, which suggests that a significant (~ 80%) reduction in aggregate sediment-phase TCE concentrations occurred between sampling events. The second method was based on fitting the temporal contaminant mass discharge data with a simple exponential source-depletion function. Relatively similar estimates, 784 and 993 kg, respectively, were obtained with the two methods. These data were used to characterize the relationship between reductions in contaminant mass discharge (CMDR) and reductions in contaminant mass (MR). The observed curvilinear relationship exhibits a reduction in contaminant mass discharge essentially immediately upon the initiation of mass reduction. This behavior is consistent with a system wherein significant quantities of mass are present in hydraulically poorly accessible domains for which mass removal is influenced by rate-limited mass transfer. The results obtained from the present study are compared to those obtained from other field studies to evaluate the impact of system properties and conditions on mass-discharge and mass-removal behavior. The results indicate that factors such as domain scale, hydraulic-gradient status (induced or natural), and flushing-solution composition had insignificant impact on the CMDR-MR profiles and thus on underlying mass-removal behavior. Conversely, source-zone age, through its impact on contaminant distribution and accessibility, was implicated as a critical factor influencing the nature of the CMDR-MR relationship. © 2013 Elsevier B.V.
• Brusseau, M. L., Matthieu, D. E., Carroll, K. C., Mainhagu, J., Morrison, C., McMillan, A., Russo, A., & Plaschke, M. (2013). Characterizing long-term contaminant mass discharge and the relationship between reductions in discharge and reductions in mass for DNAPL source areas. Journal of Contaminant Hydrology, 149.
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  The objective of this study was to characterize the temporal behavior of contaminant mass discharge, and the relationship between reductions in contaminant mass discharge and reductions in contaminant mass, for a very heterogeneous, highly contaminated source-zone field site. Trichloroethene is the primary contaminant of concern, and several lines of evidence indicate the presence of organic liquid in the subsurface. The site is undergoing groundwater extraction for source control, and contaminant mass discharge has been monitored since system startup. The results show a significant reduction in contaminant mass discharge with time, decreasing from approximately 1 to 0.15 kg/d over five years. Two methods were used to estimate the mass of contaminant present in the source area at the initiation of the remediation project. One was based on a comparison of two sets of core data, collected 3.5 years apart, which suggests that a significant (~80%) reduction in aggregate sediment-phase TCE concentrations occurred between sampling events. The second method was based on fitting the temporal contaminant mass discharge data with a simple exponential source-depletion function. Relatively similar estimates, 784 and 993 kg, respectively, were obtained with the two methods. These data were used to characterize the relationship between reductions in contaminant mass discharge (CMDR) and reductions in contaminant mass (MR). The observed curvilinear relationship exhibits a reduction in contaminant mass discharge essentially immediately upon the initiation of mass reduction. This behavior is consistent with a system wherein significant quantities of mass are present in hydraulically poorly accessible domains for which mass removal is influenced by rate-limited mass transfer. The results obtained from the present study are compared to those obtained from other field studies to evaluate the impact of system properties and conditions on mass-discharge and mass-removal behavior. The results indicate that factors such as domain scale, hydraulic-gradient status (induced or natural), and flushing-solution composition had insignificant impact on the CMDR-MR profiles and thus on underlying mass-removal behavior. Conversely, source-zone age, through its impact on contaminant distribution and accessibility, was implicated as a critical factor influencing the nature of the CMDR-MR relationship.
• Brusseau, M., Brusseau, M. L., Costanza-Robinson, M. S., & Carlson, T. D. (2013). Vapor-phase transport of trichloroethene in an intermediate-scale vadose-zone system: retention processes and tracer-based prediction. Journal of Contaminant Hydrology, 145.
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  Gas-phase transport experiments were conducted using a large weighing lysimeter to evaluate retention processes for volatile organic compounds (VOCs) in water-unsaturated (vadose-zone) systems, and to test the utility of gas-phase tracers for predicting VOC retardation. Trichloroethene (TCE) served as a model VOC, while trichlorofluoromethane (CFM) and heptane were used as partitioning tracers to independently characterize retention by water and the air-water interface, respectively. Retardation factors for TCE ranged between 1.9 and 3.5, depending on water content. The results indicate that dissolution into the bulk water was the primary retention mechanism for TCE under all conditions studied, contributing approximately two-thirds of the total measured retention. Accumulation at the air-water interface comprised a significant fraction of the observed retention for all experiments, with an average contribution of approximately 24%. Sorption to the solid phase contributed approximately 10% to retention. Water contents and air-water interfacial areas estimated based on the CFM and heptane tracer data, respectively, were similar to independently measured values. Retardation factors for TCE predicted using the partitioning-tracer data were in reasonable agreement with the measured values. These results suggest that gas-phase tracer tests hold promise for characterizing the retention and transport of VOCs in the vadose-zone.
• Carroll, K. C., Truex, M. J., Brusseau, M. L., Parker, K. R., Mackley, R. D., & Rohay, V. J. (2013). Characterization of persistent volatile contaminant sources in the vadose zone. Groundwater Monitoring and Remediation, 33(2), 68-84.
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  Abstract: Effective long-term operation of soil vapor extraction (SVE) systems for cleanup of vadose-zone sources requires consideration of the likelihood that remediation activities over time will alter the subsurface distribution and configuration of contaminants. A method is demonstrated for locating and characterizing the distribution and nature of persistent volatile organic contaminant (VOC) sources in the vadose zone. The method consists of three components: analysis of existing site and SVE-operations data, vapor-phase cyclic contaminant mass-discharge testing, and short-term vapor-phase contaminant mass-discharge tests conducted in series at multiple locations. Results obtained from the method were used to characterize overall source zone mass-transfer limitations, source-strength reductions, potential changes in source-zone architecture, and the spatial variability and extent of the persistent source(s) for the Department of Energy's Hanford site. The results confirmed a heterogeneous distribution of contaminant mass discharge throughout the vadose zone. Analyses of the mass-discharge profiles indicate that the remaining contaminant source is coincident with a lower-permeability unit at the site. Such measurements of source strength and size as obtained herein are needed to determine the impacts of vadose-zone sources on groundwater contamination and vapor intrusion, and can support evaluation and optimization of the performance of SVE operations. © 2013, National Ground Water Association.
• Costanza-Robinson, M. S., Carlson, T. D., & Brusseau, M. L. (2013). Vapor-phase transport of trichloroethene in an intermediate-scale vadose-zone system: Retention processes and tracer-based prediction. Journal of Contaminant Hydrology, 145, 82-89.
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  PMID: 23333418;PMCID: PMC3650913;Abstract: Gas-phase transport experiments were conducted using a large weighing lysimeter to evaluate retention processes for volatile organic compounds (VOCs) in water-unsaturated (vadose-zone) systems, and to test the utility of gas-phase tracers for predicting VOC retardation. Trichloroethene (TCE) served as a model VOC, while trichlorofluoromethane (CFM) and heptane were used as partitioning tracers to independently characterize retention by water and the air-water interface, respectively. Retardation factors for TCE ranged between 1.9 and 3.5, depending on water content. The results indicate that dissolution into the bulk water was the primary retention mechanism for TCE under all conditions studied, contributing approximately two-thirds of the total measured retention. Accumulation at the air-water interface comprised a significant fraction of the observed retention for all experiments, with an average contribution of approximately 24%. Sorption to the solid phase contributed approximately 10% to retention. Water contents and air-water interfacial areas estimated based on the CFM and heptane tracer data, respectively, were similar to independently measured values. Retardation factors for TCE predicted using the partitioning-tracer data were in reasonable agreement with the measured values. These results suggest that gas-phase tracer tests hold promise for characterizing the retention and transport of VOCs in the vadose-zone. © 2012 Elsevier B.V.
• Izady, A., Davary, K., Alizadeh, A., Ziaei, A. N., Alipoor, A., Joodavi, A., & Brusseau, M. L. (2013). A framework toward developing a groundwater conceptual model. Arabian Journal of Geosciences, 1-21.
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  Abstract: Developing an accurate conceptual model is the most important step in the process of a groundwater numerical modeling. Disorganized and limited available data and information, especially in the developing countries, make the preparation of the conceptual model difficult and sometimes cumbersome. In this research, an integrative and comprehensive method is proposed to develop groundwater conceptual model for an unconfined aquifer. The proposed method consists of six steps. A preliminary step (step 0) is aimed at collecting all the available data and information. The output of the first step as "controlling observations" is conceptual model version 00. This step should be rigorously checked due to its critical role in the controlling of final conceptual model. Step 2 determines the aquifer geometry. The output of this step is conceptual model version 01. Step 3 is responsible to determine hydrodynamic properties and its output develops conceptual model version 02. Step 4 evaluates the surface and subsurface interactions and lateral in/out groundwater flows. The output of this step is conceptual model version 03. Step 5 is to integrate the results from other steps and to deliver the final conceptual model version. The accuracy level of the conceptual model and the annual groundwater balance is also determined at this step. The presented groundwater conceptual model procedure was implemented for the Neishaboor plain, Iran. Results showed its usefulness and practicality in developing the conceptual model for the study area. © 2013 Saudi Society for Geosciences.
• Matthieu, D. E., Brusseau, M. L., Johnson, G. R., Artiola, J. L., Bowden, M. L., & Curry, J. E. (2013). Intercalation of trichloroethene by sediment-associated clay minerals. Chemosphere, 90(2), 459-463.
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  PMID: 22921434;PMCID: PMC3548623;Abstract: The objective of this research was to examine the potential for intercalation of trichloroethene (TCE) by clay minerals associated with aquifer sediments. Sediment samples were collected from a field site in Tucson, AZ. Two widely used Montmorillonite specimen clays were employed as controls. X-ray diffraction, conducted with a controlled-environment chamber, was used to characterize smectite interlayer d-spacing for three treatments (bulk air-dry sample, sample mixed with synthetic groundwater, sample mixed with TCE-saturated synthetic groundwater). The results show that the d-spacing measured for the samples treated with TCE-saturated synthetic groundwater are larger (∼26%) than those of the untreated samples for all field samples as well as the specimen clays. These results indicate that TCE was intercalated by the clay minerals, which may have contributed to the extensive elution tailing observed in prior miscible-displacement experiments conducted with this sediment. © 2012 Elsevier Ltd.
• Matthieu, D. E., Brusseau, M. L., Johnson, G. R., Artiola, J. L., Bowden, M. L., & Curry, J. E. (2013). Intercalation of trichloroethene by sediment-associated clay minerals. Chemosphere, 90(2).
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  The objective of this research was to examine the potential for intercalation of trichloroethene (TCE) by clay minerals associated with aquifer sediments. Sediment samples were collected from a field site in Tucson, AZ. Two widely used Montmorillonite specimen clays were employed as controls. X-ray diffraction, conducted with a controlled-environment chamber, was used to characterize smectite interlayer d-spacing for three treatments (bulk air-dry sample, sample mixed with synthetic groundwater, sample mixed with TCE-saturated synthetic groundwater). The results show that the d-spacing measured for the samples treated with TCE-saturated synthetic groundwater are larger (~26%) than those of the untreated samples for all field samples as well as the specimen clays. These results indicate that TCE was intercalated by the clay minerals, which may have contributed to the extensive elution tailing observed in prior miscible-displacement experiments conducted with this sediment.
• Miao, Z., Akyol, H. N., McMillan, A. L., & Brusseau, M. L. (2013). Transport and fate of ammonium and its impact on uranium and other trace elements at a former uranium mill tailing site. Applied Geochemistry, 38, 24-32.
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  Abstract: The remediation of ammonium-containing groundwater discharged from uranium mill tailing sites is a difficult problem facing the mining industry. The Monument Valley site is a former uranium mining site in the southwest US with both ammonium and nitrate contamination of groundwater. In this study, samples collected from 14 selected wells were analyzed for major cations and anions, trace elements, and isotopic composition of ammonium and nitrate. In addition, geochemical data from the U.S. Department of Energy (DOE) database were analyzed. Results showing oxic redox conditions and correspondence of isotopic compositions of ammonium and nitrate confirmed the natural attenuation of ammonium via nitrification. Moreover, it was observed that ammonium concentration within the plume area is closely related to concentrations of uranium and a series of other trace elements including chromium, selenium, vanadium, iron, and manganese. It is hypothesized that ammonium-nitrate transformation processes influence the disposition of the trace elements through mediation of redox potential, pH, and possibly aqueous complexation and solid-phase sorption. Despite the generally relatively low concentrations of trace elements present in groundwater, their transport and fate may be influenced by remediation of ammonium or nitrate at the site. © 2013 Elsevier Ltd.
• Miao, Z., Carroll, K. C., & Brusseau, M. L. (2013). Characterization and quantification of groundwater sulfate sources at a mining site in an arid climate: The Monument Valley site in Arizona, USA. Journal of Hydrology, 504, 207-215.
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  Abstract: The Monument Valley site, a former uranium mining site located in the state of Arizona in the Southwest USA, has high concentrations of sulfate in groundwater. Stable isotope analysis of S and O for sulfate, in combination with geochemical and hydrogeological data, was used to characterize the sources and fate of sulfate. The results indicate the existence of two discrete sources of sulfate (in excess of baseline levels): sulfuric acid released during ore processing and sulfate generated via sulfide-mineral oxidation. The contributions of the sources are related to spatial distributions of sulfate in the plume through analysis of groundwater travel times. Quantification of the sources using two isotope-analysis methods yielded similar results. The results indicate that sulfuric acid served as the primary source (mean. = 427. mg/L, 74%), with sulfide-mineral oxidation providing a smaller contribution (mean. = 147. mg/L, 26%). It appears that the major contribution to the sulfide-mineral oxidation component originates from oxidation of sulfide minerals in exposed bedrock residing in the primary recharge zone of the local aquifer, which provides an elevated sulfate background for groundwater. Conversely, the oxidation of sulfide minerals associated with the mine tailings appears to provide a relatively minor contribution (~8% of the overall total). Interestingly, it appears that sulfuric acid served as a sustained source of sulfate for approximately 40. years. This may be related to the accumulation of sulfate salts (formed after neutralization and disposal of the sulfuric acid) in the source zone due to the arid climate of the site. Contrary to the typical assumption applied at many mining sites that sulfide-mineral oxidation is the primary source of sulfate, these sulfate salts are hypothesized to be the primary source for this site. © 2013 Elsevier B.V.
• Miao, Z., Nihat, H., McMillan, A. L., & Brusseau, M. L. (2013). Transport and fate of ammonium and its impact on uranium and other trace elements at a former uranium mill tailing site. Applied Geochemistry : Journal of the International Association of Geochemistry and Cosmochemistry, 38.
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  The remediation of ammonium-containing groundwater discharged from uranium mill tailing sites is a difficult problem facing the mining industry. The Monument Valley site is a former uranium mining site in the southwest US with both ammonium and nitrate contamination of groundwater. In this study, samples collected from 14 selected wells were analyzed for major cations and anions, trace elements, and isotopic composition of ammonium and nitrate. In addition, geochemical data from the U.S. Department of Energy (DOE) database were analyzed. Results showing oxic redox conditions and correspondence of isotopic compositions of ammonium and nitrate confirmed the natural attenuation of ammonium via nitrification. Moreover, it was observed that ammonium concentration within the plume area is closely related to concentrations of uranium and a series of other trace elements including chromium, selenium, vanadium, iron, and manganese. It is hypothesized that ammonium-nitrate transformation processes influence the disposition of the trace elements through mediation of redox potential, pH, and possibly aqueous complexation and solid-phase sorption. Despite the generally relatively low concentrations of trace elements present in groundwater, their transport and fate may be influenced by remediation of ammonium or nitrate at the site.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J. F., & Maier, R. M. (2013). A greenhouse and field-based study to determine the accumulation of arsenic in common homegrown vegetables grown in mining-affected soils. Science of the Total Environment, 443, 299-306.
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  PMID: 23201696;PMCID: PMC3649874;Abstract: The uptake of arsenic by plants from contaminated soils presents a health hazard that may affect home gardeners neighboring contaminated environments. A controlled greenhouse study was conducted in parallel with a co-created citizen science program (home garden experiment) to characterize the uptake of arsenic by common homegrown vegetables near the Iron King Mine and Humboldt Smelter Superfund site in southern Arizona. The greenhouse and home garden arsenic soil concentrations varied considerably, ranging from 2.35 to 533mgkg-1. In the greenhouse experiment four vegetables were grown in three different soil treatments and in the home garden experiment a total of 63 home garden produce samples were obtained from 19 properties neighboring the site. All vegetables accumulated arsenic in both the greenhouse and home garden experiments, ranging from 0.01 to 23.0mgkg-1 dry weight. Bioconcentration factors were determined and show that arsenic uptake decreased in the order: Asteraceae>Brassicaceae>Amaranthaceae>Cucurbitaceae>Liliaceae>Solanaceae>Fabaceae. Certain members of the Asteraceae and Brassicaceae plant families have been previously identified as hyperaccumulator plants, and it can be inferred that members of these families have genetic and physiological capacity to accumulate, translocate, and resist high amounts of metals. Additionally, a significant linear correlation was observed between the amount of arsenic that accumulated in the edible portion of the plant and the arsenic soil concentration for the Asteraceae, Brassicaceae, Amaranthaceae, and Fabaceae families. The results suggest that home gardeners neighboring mining operations or mine tailings with elevated arsenic levels should be made aware that arsenic can accumulate considerably in certain vegetables, and in particular, it is recommended that gardeners limit consumption of vegetables from the Asteraceae and Brassicaceae plant families. © 2012 Elsevier B.V.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J. F., & Maier, R. M. (2013). A greenhouse and field-based study to determine the accumulation of arsenic in common homegrown vegetables grown in mining-affected soils. The Science of the total environment, 443.
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  The uptake of arsenic by plants from contaminated soils presents a health hazard that may affect home gardeners neighboring contaminated environments. A controlled greenhouse study was conducted in parallel with a co-created citizen science program (home garden experiment) to characterize the uptake of arsenic by common homegrown vegetables near the Iron King Mine and Humboldt Smelter Superfund site in southern Arizona. The greenhouse and home garden arsenic soil concentrations varied considerably, ranging from 2.35 to 533 mg kg(-1). In the greenhouse experiment four vegetables were grown in three different soil treatments and in the home garden experiment a total of 63 home garden produce samples were obtained from 19 properties neighboring the site. All vegetables accumulated arsenic in both the greenhouse and home garden experiments, ranging from 0.01 to 23.0 mg kg(-1) dry weight. Bioconcentration factors were determined and show that arsenic uptake decreased in the order: Asteraceae>Brassicaceae>Amaranthaceae>Cucurbitaceae>Liliaceae>Solanaceae>Fabaceae. Certain members of the Asteraceae and Brassicaceae plant families have been previously identified as hyperaccumulator plants, and it can be inferred that members of these families have genetic and physiological capacity to accumulate, translocate, and resist high amounts of metals. Additionally, a significant linear correlation was observed between the amount of arsenic that accumulated in the edible portion of the plant and the arsenic soil concentration for the Asteraceae, Brassicaceae, Amaranthaceae, and Fabaceae families. The results suggest that home gardeners neighboring mining operations or mine tailings with elevated arsenic levels should be made aware that arsenic can accumulate considerably in certain vegetables, and in particular, it is recommended that gardeners limit consumption of vegetables from the Asteraceae and Brassicaceae plant families.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Beamer, P., & Maier, R. M. (2013). Home gardening near a mining site in an arsenic-endemic region of Arizona: Assessing arsenic exposure dose and risk via ingestion of home garden vegetables, soils, and water. Science of the Total Environment, 454-455, 373-382.
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  PMID: 23562690;PMCID: PMC3871205;Abstract: The human-health risk posed by gardening near a legacy mine and smelter in an arsenic-endemic region of Arizona was characterized in this study. Residential soils were used in a greenhouse study to grow common vegetables, and local residents, after training, collected soil, water, and vegetables samples from their home gardens. Concentrations of arsenic measured in water, soil, and vegetable samples were used in conjunction with reported US intake rates to calculate the daily dose, Incremental Excess Lifetime Cancer Risk (IELCR), and Hazard Quotient for arsenic. Relative arsenic intake dose decreased in order: water>garden soils>homegrown vegetables, and on average, each accounted for 77, 16, and 7% of a residential gardener's daily arsenic intake dose. The IELCR ranges for vegetables, garden soils, and water were 10-8 to 10-4, 10-6 to 10-4, and 10-5 to 10-2, respectively. All vegetables (greenhouse and home garden) were grouped by scientific family, and the risk posed decreased as: Asteraceae>Fabaceae>Amaranthaceae>Liliaceae>Brassicaceae>Solanaceae>Cucurbitaceae. Correlations observed between concentrations of arsenic in vegetables and soils were used to estimate a maximum allowable level of arsenic in soil to limit the excess cancer risk to 10-6. The estimated values are 1.56mgkg-1, 5.39mgkg-1, 11.6mgkg-1 and 12.4mgkg-1 for the Asteraceae, Brassicaceae, Fabaceae, and Amaranthaceae families, respectively. It is recommended that home gardeners: sample their private wells annually, test their soils prior to gardening, and, if necessary, modify their gardening behavior to reduce incidental soil ingestion. This study highlights the importance of site-specific risk assessment, and the need for species-specific planting guidelines for communities. © 2013 Elsevier B.V.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Beamer, P., & Maier, R. M. (2013). Home gardening near a mining site in an arsenic-endemic region of Arizona: assessing arsenic exposure dose and risk via ingestion of home garden vegetables, soils, and water. The Science of the total environment, 454-455.
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  The human-health risk posed by gardening near a legacy mine and smelter in an arsenic-endemic region of Arizona was characterized in this study. Residential soils were used in a greenhouse study to grow common vegetables, and local residents, after training, collected soil, water, and vegetables samples from their home gardens. Concentrations of arsenic measured in water, soil, and vegetable samples were used in conjunction with reported US intake rates to calculate the daily dose, Incremental Excess Lifetime Cancer Risk (IELCR), and Hazard Quotient for arsenic. Relative arsenic intake dose decreased in order: water>garden soils>homegrown vegetables, and on average, each accounted for 77, 16, and 7% of a residential gardener's daily arsenic intake dose. The IELCR ranges for vegetables, garden soils, and water were 10(-8) to 10(-4), 10(-6) to 10(-4), and 10(-5) to 10(-2), respectively. All vegetables (greenhouse and home garden) were grouped by scientific family, and the risk posed decreased as: Asteraceae≫Fabaceae>Amaranthaceae>Liliaceae>Brassicaceae>Solanaceae≫Cucurbitaceae. Correlations observed between concentrations of arsenic in vegetables and soils were used to estimate a maximum allowable level of arsenic in soil to limit the excess cancer risk to 10(-6). The estimated values are 1.56 mg kg(-1), 5.39 mg kg(-1), 11.6 mg kg(-1) and 12.4 mg kg(-1) for the Asteraceae, Brassicaceae, Fabaceae, and Amaranthaceae families, respectively. It is recommended that home gardeners: sample their private wells annually, test their soils prior to gardening, and, if necessary, modify their gardening behavior to reduce incidental soil ingestion. This study highlights the importance of site-specific risk assessment, and the need for species-specific planting guidelines for communities.
• Schnaar, G., & Brusseau, M. L. (2013). Measuring equilibrium sorption coefficients with the miscible-displacement method. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 48(4), 355-359.
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  PMID: 23379939;PMCID: PMC3576931;Abstract: The miscible-displacement method is one commonly used approach for measuring equilibrium sorption coefficients. The objective of this research was to examine the impact of experiment conditions (detection limit, input-pulse size, input concentration) on the measurement of retardation factors and sorption coefficients for a system that exhibits significant nonideal sorption behavior. A series of miscible-displacement experiments was conducted wherein effluent solute concentrations were monitored over a range of approximately seven orders of magnitude, allowing characterization of asymptotic tailing phenomenon, which was significant. The magnitude of Kd increased asymptotically with the increase in the extent of the elution tail measured. The results also showed that the fraction of the tail required to obtain close-to-maximum measures of Kd is greater for smaller input pulses. Investigating the impact of analytical detection limit (equivalent to relative concentrations of 10-3 and 10-7) revealed that the magnitude of Kd was invariant with input pulse for the 10 -7 detection limit. Conversely, the measured Kd values were significantly smaller at low input pulses for the 10-3 detection limit. © 2013 Copyright Taylor and Francis Group, LLC.
• Schnaar, G., & Brusseau, M. L. (2013). Measuring equilibrium sorption coefficients with the miscible-displacement method. Journal of Environmental Science and Health. Part A, Toxic/hazardous substances & environmental engineering, 48(4).
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  The miscible-displacement method is one commonly used approach for measuring equilibrium sorption coefficients. The objective of this research was to examine the impact of experiment conditions (detection limit, input-pulse size, input concentration) on the measurement of retardation factors and sorption coefficients for a system that exhibits significant nonideal sorption behavior. A series of miscible-displacement experiments was conducted wherein effluent solute concentrations were monitored over a range of approximately seven orders of magnitude, allowing characterization of asymptotic tailing phenomenon, which was significant. The magnitude of K(d) increased asymptotically with the increase in the extent of the elution tail measured. The results also showed that the fraction of the tail required to obtain close-to-maximum measures of K(d) is greater for smaller input pulses. Investigating the impact of analytical detection limit (equivalent to relative concentrations of 10(-3) and 10(-7)) revealed that the magnitude of K(d) was invariant with input pulse for the 10(-7) detection limit. Conversely, the measured K(d) values were significantly smaller at low input pulses for the 10(-3) detection limit.
• , J., Brusseau, M., Araujo, J., Orosz-Coghlan, P., Blanford, W., & Gerba, C. (2012). Transport and Retention of Cryptosporidium Parvum Oocysts in Sandy Soils. Journal of Environmental Quality, 41, 1246-1252.
• Borden, A., Brusseau, M., Carroll, K., McMillan, A., Akyol, N., Berkompas, J., Miao, Z., Jordan, F., Tick, G., Waugh, W., & Glenn, E. (2012). Ethanol Addition for Enhancing Denitrification at the Uranium Mill Tailing Site in Monument Valley, Arizona. Water, Air, Soil Pollution, 223, 755-763.
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  DOI 10.1007/s11270-011-0899-1
• Brusseau, M. L., Russo, A. E., & Schnaar, G. (2012). Nonideal transport of contaminants in heterogeneous porous media: 9 - Impact of contact time on desorption and elution tailing. Chemosphere, 89(3), 287-292.
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  PMID: 22608708;PMCID: PMC3406242;Abstract: A series of miscible-displacement experiments was conducted to examine the impact of sorption contact time on desorption and elution of trichloroethene from a well-characterized soil. A large number of contact times were examined, spanning 1h to 4years (∼2×106h). Effluent trichloroethene concentrations were monitored over a range of greater than six orders of magnitude, allowing characterization of potential asymptotic tailing. The results of the column experiments showed that trichloroethene exhibited extensive elution tailing for all experiments. Each increase in contact time resulted in a successive increase in the extent of tailing. In total, the number of pore volumes of water flushing required to reach the analytical detection limit increased from approximately 1000 for the 1-h contact time to almost 9000 for the 4-year contact time. These results indicate that a contact time of less than 1h produced a sorbed phase that is relatively resistant to desorption, and that a progressive increase in resistance to desorption occurred with increased contact time. A mathematical model incorporating nonlinear, rate-limited sorption/desorption described by a continuous-distribution reaction function was used to successfully simulate the measured data. The nonlinear sorption, the apparent rapid development of desorption resistance, and the progressive increase in resistance with increasing contact time are consistent with behavior anticipated for sorbate interactions with hard-carbon components of the soil. © 2012 Elsevier Ltd.
• Brusseau, M. L., Schnaar, G., Johnson, G. R., & Russo, A. E. (2012). Nonideal transport of contaminants in heterogeneous porous media: 10. Impact of co-solutes on sorption by porous media with low organic-carbon contents. Chemosphere, 89(11), 1302-1306.
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  PMID: 22717163;PMCID: PMC3575748;Abstract: The impact of co-solutes on sorption of tetrachloroethene (PCE) by two porous media with low organic-carbon contents was examined by conducting batch experiments. The two media (Borden and Eustis) have similar physical properties, but significantly different organic-carbon (OC) contents. Sorption of PCE was nonlinear for both media, and well-described by the Freundlich equation. For the Borden aquifer material (OC = 0.03%), the isotherms measured with a suite of co-solutes present (1,2-dichlorobenzene, bromoform, carbon tetrachloride, and hexachloroethane) were identical to the isotherms measured for PCE alone. These results indicate that there was no measurable impact of the co-solutes on PCE sorption for this system. In contrast to the Borden results, there was a measurable reduction in sorption of PCE by the Eustis soil (OC = 0.38%) in the presence of the co-solutes. The organic-carbon fractions of both media contain hard-carbon components, which have been associated with the manifestation of nonideal sorption phenomena. The disparity in results observed for the two media may relate to relative differences in the magnitude and geochemical nature of these hard-carbon components. © 2012.
• Brusseau, M., Russo, A., & Schnaar, G. (2012). Nonideal Transport of Contaminants in Heterogeneous Porous Media: 9- Impact of Contact Time on Desorption and Elution Tailing. Chemosphere, 89, 287-292.
• Brusseau, M., Schnaar, G., Johnson, G., & Russo, A. (2012). Nonideal Transport of Contaminants in Heterogeneous Porous Media: 10- Impact of Co-solutes on Sorption by Porous Media with Low Organic-Carbon Contents.. Chemosphere, 89, 1302-1306.
• Carroll, K. C., Oostrom, M., Truex, M. J., Rohay, V. J., & Brusseau, M. L. (2012). Assessing performance and closure for soil vapor extraction: Integrating vapor discharge and impact to groundwater quality. Journal of Contaminant Hydrology, 128(1-4), 71-82.
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  PMID: 22192346;Abstract: Soil vapor extraction (SVE) is typically effective for removal of volatile contaminants from higher-permeability portions of the vadose zone. However, contamination in lower-permeability zones can persist due to mass transfer processes that limit the removal effectiveness. After SVE has been operated for a period of time and the remaining contamination is primarily located in lower-permeability zones, the remedy performance needs to be evaluated to determine whether the SVE system should be optimized, terminated, or transitioned to another technology to replace or augment SVE. Numerical modeling of vapor-phase contaminant transport was used to investigate the correlation between measured vapor-phase mass discharge, MF r, from a persistent, vadose-zone contaminant source and the resulting groundwater contaminant concentrations. This relationship was shown to be linear, and was used to directly assess SVE remediation progress over time and to determine the level of remediation in the vadose zone necessary to protect groundwater. Although site properties and source characteristics must be specified to establish a unique relation between MF r and the groundwater contaminant concentration, this correlation provides insight into SVE performance and support for decisions to optimize or terminate the SVE operation or to transition to another type of treatment. © 2011 Elsevier B.V. All rights reserved.
• Carroll, K., Oostrom, M., Truex, M., Rohay, V., & Brusseau, M. (2012). Assessing Performance and Closure for Soil Vapor Extraction: Integrating Vapor Discharge and Impact to Groundwater Quality. Journal of Contaminant Hydrology, 128, 71-82.
• Miao, Z., Brusseau, M. L., Carroll, K. C., Carreón-Diazconti, C., & Johnson, B. (2012). Sulfate reduction in groundwater: Characterization and applications for remediation. Environmental Geochemistry and Health, 34(4), 539-550.
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  PMID: 21947714;PMCID: PMC3575751;Abstract: Sulfate is ubiquitous in groundwater, with both natural and anthropogenic sources. Sulfate reduction reactions play a significant role in mediating redox conditions and biogeochemical processes for subsurface systems. They also serve as the basis for innovative in situ methods for groundwater remediation. An overview of sulfate reduction in subsurface environments is provided, along with a brief discussion of characterization methods and applications for addressing acid mine drainage. We then focus on two innovative, in situ methods for remediating sulfate-contaminated groundwater, the use of zero-valent iron and the addition of electron-donor substrates. The advantages and limitations associated with the methods are discussed, with examples of prior applications. © 2011 Springer Science+Business Media B.V.
• Miao, Z., Brusseau, M., Carroll, K., , C., & Johnson, B. (2012). Sulfate Reduction In Groundwater: Characterization and Applications for Remediation. Environmental Geochemistry and Health, 34, 539-550.
• Peng, S., & Brusseau, M. (2012). Air-water Interfacial Area and Capillary Pressure: Porous-medium Texture Effects and an Empirical Function. Journal of Hydrologic Engineering, 17, 829-832.
• Peng, S., & Brusseau, M. L. (2012). Air-water interfacial area and capillary pressure: Porous-Medium texture effects and an empirical function. Journal of Hydrologic Engineering, 17(7), 829-832.
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  Abstract: The relationship between air-water interfacial area and capillary pressure under higher water-content conditions is investigated for four natural porous media. The results show that the magnitude of the air-water interfacial area increases with increasing capillary pressure, consistent with the decrease in water saturation. The maximum observed air-water interfacial areas are dependent upon the magnitude of residual water saturation, which itself is condition-dependent. The more well-sorted porous-medium exhibited a greater rate of change of air-water interfacial area with capillary pressure than the more poorly sorted porous media. The observed relationship between air-water interfacial area and capillary pressure was quantified by coupling an empirical equation describing the air-water interfacial area versus water saturation relationship with the van Genuchten equation relating water saturation and capillary pressure. This equation produced reasonable simulations of the measured data. © 2012 American Society of Civil Engineers.
• , J., Quinonez-Diaz, M., LeMond, L., Arnold, R., Quanrud, D., Gerba, C., & Brusseau, M. (2011). Transport of Cryptosporidium Parvum Oocysts in a Sandy Soil: Impact of Length Scale. Journal of Environmental Monitoring, 13, 3481-3484.
• Brusseau, M. L., Carroll, K. C., Allen, T., Baker, J., Diguiseppi, W., Hatton, J., Morrison, C., Russo, A., & Berkompas, J. (2011). Impact of in situ chemical oxidation on contaminant mass discharge: Linking source-zone and plume-scale characterizations of remediation performance. Environmental Science and Technology, 45(12), 5352-5358.
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  PMID: 21615133;PMCID: PMC3157310;Abstract: A large-scale permanganate-based in situ chemical oxidation (ISCO) effort has been conducted over the past ten years at a federal Superfund site in Tucson, AZ, for which trichloroethene (TCE) is the primary contaminant of concern. Remediation performance was assessed by examining the impact of treatment on contaminant mass discharge, an approach that has been used for only a very few prior ISCO projects. Contaminant mass discharge tests were conducted before and after permanganate injection to measure the impact at the source-zone scale. The results indicate that ISCO caused a significant reduction in mass discharge (approximately 75%). The standard approach of characterizing discharge at the source-zone scale was supplemented with additional characterization at the plume scale, which was evaluated by examining the change in contaminant mass discharge associated with the pump-and-treat system. The integrated contaminant mass discharge decreased by approximately 70%, consistent with the source-zone-scale measurements. The integrated mass discharge rebounded from 0.1 to 0.2 kg/d within one year after cessation of permanganate injections, after which it has been stable for several years. Collection of the integrated contaminant mass discharge data throughout the ISCO treatment period provided a high-resolution, real-time analysis of the site-wide impact of ISCO, thereby linking source-zone remediation to impacts on overall risk. The results indicate that ISCO was successful in reducing contaminant mass discharge at this site, which comprises a highly heterogeneous subsurface environment. Analysis of TCE sediment concentration data for core material collected before and after ISCO supports the hypothesis that the remaining mass discharge is associated in part with poorly accessible contaminant mass residing within lower-permeability zones. © 2011 American Chemical Society.
• Brusseau, M. L., Hatton, J., & Diguiseppi, W. (2011). Assessing the impact of source-zone remediation efforts at the contaminant-plume scale through analysis of contaminant mass discharge. Journal of Contaminant Hydrology, 126(3-4), 130-139.
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  PMID: 22115080;PMCID: PMC3224343;Abstract: The long-term impact of source-zone remediation efforts was assessed for a large site contaminated by trichloroethene. The impact of the remediation efforts (soil vapor extraction and in-situ chemical oxidation) was assessed through analysis of plume-scale contaminant mass discharge, which was measured using a high-resolution data set obtained from 23 years of operation of a large pump-and-treat system. The initial contaminant mass discharge peaked at approximately 7 kg/d, and then declined to approximately 2 kg/d. This latter value was sustained for several years prior to the initiation of source-zone remediation efforts. The contaminant mass discharge in 2010, measured several years after completion of the two source-zone remediation actions, was approximately 0.2 kg/d, which is ten times lower than the value prior to source-zone remediation. The time-continuous contaminant mass discharge data can be used to evaluate the impact of the source-zone remediation efforts on reducing the time required to operate the pump-and-treat system, and to estimate the cost savings associated with the decreased operational period. While significant reductions have been achieved, it is evident that the remediation efforts have not completely eliminated contaminant mass discharge and associated risk. Remaining contaminant mass contributing to the current mass discharge is hypothesized to comprise poorly accessible mass in the source zones, as well as aqueous (and sorbed) mass present in the extensive lower-permeability units located within and adjacent to the contaminant plume. The fate of these sources is an issue of critical import to the remediation of chlorinated-solvent contaminated sites, and development of methods to address these sources will be required to achieve successful long-term management of such sites and to ultimately transition them to closure. © 2011 Elsevier B.V. All rights reserved.
• Brusseau, M., Carroll, K., Allen, T., Baker, J., DiGuiseppi, W., Hatton, J., Morrison, C., Russo, A., & Berkompas, J. (2011). The Impact of In-situ Chemical Oxidation on Contaminant Mass Discharge: Linking Source-zone and Plume-scale Characterizations of Remediation Performance. Environmental Science & Technology, 45, 5352-5358.
• Brusseau, M., DiFilippo, E. L., & Brusseau, M. L. (2011). Assessment of a simple function to evaluate the relationship between mass flux reduction and mass removal for organic-liquid contaminated source zones. Journal of contaminant hydrology, 123(3-4).
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  The efficacy of a simple mass-removal function for characterizing mass-flux-reduction/mass-removal behavior for organic-liquid contaminated source zones was evaluated using the data obtained from a series of flow-cell experiments. The standard function, which employs a constant exponent, could not adequately reproduce the non-singular (multi-step) behavior exhibited by the measured data. Allowing the exponent to change as a function of mass removal (as the organic-liquid distribution and relative permeability change) produced non-singular relationships similar to those exhibited by the measured data. Four methods were developed to dynamically inform the exponent through use of measurable system-indicator parameters. Key factors that mediate the magnitude of mass flux (dilution and source accessibility) were accounted for using measures of source zone cross-sectional area, ganglia-to-pool (GTP) ratio, and relative permeability. The two methods that incorporated only the ganglia-to-pool ratio produced adequate simulations of the observed behavior for early stages of mass removal, but not for later stages. The method that incorporated parameters accounting for the source zone cross-sectional area (i.e., measure of system dilution) and source accessibility (GTP ratio and relative permeability) provided the most representative simulations of the observed data.
• Brusseau, M., Hatton, J., & DiGuiseppi, W. (2011). Assessing The Impact of Source-Zone Remediation Efforts at the Contaminant-Plume Scale: Application to a Chlorinated-Solvent Site. Journal of Contaminant Hydrology, 126, 130-139.
• Brusseau, M., Santamaría, J., Quinonez-Diaz, M. d., Lemond, M., Arnold, M., Quanrud, M., Gerba, M., & Brusseau, M. L. (2011). Transport of Cryptosporidium parvum oocysts in sandy soil: impact of length scale. Journal of environmental monitoring : JEM, 13(12).
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  The objective of this study was to investigate the impact of length scale (travel distance) on the retention and transport of Cryptosporidium oocysts in a sandy soil. Long columns (1 and 2 meters) and an in situ lysimeter (4 m) were used to allow investigation of larger-scale transport under controlled conditions. Significant retention of oocysts was observed, with the magnitude of removal from solution ranging between 2 to 5 logs. While the removal was greater for longer travel distances (or residence times), the increase was not log-linear. This observation indicates that oocyst transport was not consistent with standard colloid filtration theory. The observed behavior is speculated to arise, at least in part, from intrapopulation variability in oocyst properties. The results of this study indicate that while Cryptosporidium oocysts may be expected to experience significant retention and removal during transport in sandy soil, the magnitude of retention may be less than that which would be predicted by applying standard colloid filtration theory to the results of typical short-column experiments. Thus, a fraction of the oocysts may be more mobile than anticipated and thereby pose a greater than expected risk to groundwater.
• DiFilippo, E., & Brusseau, M. (2011). Application of Light Reflection Visualization for Measuring Organic-Liquid Saturation for Two-Phase Systems in Two-Dimensional Flow Cells. Environmental Engineering Science, 28, 803-809.
• DiFilippo, E., & Brusseau, M. (2011). Assessment of a Simple Function to Evaluate the Relationship Between Mass Flux Reduction and Mass Removal for Organic-liquid Contaminated Source Zones. Journal of Contaminant Hydrology, 123, 104-113.
• Difilippo, E. L., & Brusseau, M. L. (2011). Application of light reflection visualization for measuring organic-liquid saturation for two-phase systems in two-dimensional flow cells. Environmental Engineering Science, 28(11), 803-809.
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  Abstract: A simple, noninvasive imaging technique was used to obtain in situ measurements of organic-liquid saturation in a two-phase system under dynamic conditions. Efficacy of the light reflection visualization (LRV) imaging method was tested through comparison of measured and known volumes of organic liquid for experiments conducted with a two-dimensional flow cell. Two sets of experiments were conducted, with source-zone configurations representing two archetypical residual-and-pool architectures. LRV measurements were collected during the injection of organic liquid and during a dissolution phase induced by water flushing. There was a strong correlation between measured and known organic-liquid volumes, with the LRV-measured values generally somewhat lower than the known volumes. Errors were greater for the system wherein organic liquid was present in multiple zones comprised of porous media of different permeabilities, and for conditions of multiphase flow. This method proved effective at determining organic-liquid distribution in a two-phase system using minimal specialized equipment. © 2011, Mary Ann Liebert, Inc.
• Difilippo, E. L., & Brusseau, M. L. (2011). Assessment of a simple function to evaluate the relationship between mass flux reduction and mass removal for organic-liquid contaminated source zones. Journal of Contaminant Hydrology, 123(3-4), 104-113.
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  PMID: 21262552;PMCID: PMC3061350;Abstract: The efficacy of a simple mass-removal function for characterizing mass-flux-reduction/mass-removal behavior for organic-liquid contaminated source zones was evaluated using the data obtained from a series of flow-cell experiments. The standard function, which employs a constant exponent, could not adequately reproduce the non-singular (multi-step) behavior exhibited by the measured data. Allowing the exponent to change as a function of mass removal (as the organic-liquid distribution and relative permeability change) produced non-singular relationships similar to those exhibited by the measured data. Four methods were developed to dynamically inform the exponent through use of measurable system-indicator parameters. Key factors that mediate the magnitude of mass flux (dilution and source accessibility) were accounted for using measures of source zone cross-sectional area, ganglia-to-pool (GTP) ratio, and relative permeability. The two methods that incorporated only the ganglia-to-pool ratio produced adequate simulations of the observed behavior for early stages of mass removal, but not for later stages. The method that incorporated parameters accounting for the source zone cross-sectional area (i.e.; measure of system dilution) and source accessibility (GTP ratio and relative permeability) provided the most representative simulations of the observed data. © 2010 Elsevier B.V.
• McCray, J. E., Tick, G. R., Jawitz, J. W., Gierke, J. S., Brusseau, M. L., Falta, R. W., Knox, R. C., Sabatini, D. A., Annable, M. D., Harwell, J. H., & Wood, A. L. (2011). Remediation of NAPL source zones: Lessons learned from field studies at Hill and Dover AFB. Ground Water, 49(5), 727-744.
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  PMID: 21299555;Abstract: Innovative remediation studies were conducted between 1994 and 2004 at sites contaminated by nonaqueous phase liquids (NAPLs) at Hill and Dover AFB, and included technologies that mobilize, solubilize, and volatilize NAPL: air sparging (AS), surfactant flushing, cosolvent flooding, and flushing with a complexing-sugar solution. The experiments proved that aggressive remedial efforts tailored to the contaminant can remove more than 90% of the NAPL-phase contaminant mass. Site-characterization methods were tested as part of these field efforts, including partitioning tracer tests, biotracer tests, and mass-flux measurements. A significant reduction in the groundwater contaminant mass flux was achieved despite incomplete removal of the source. The effectiveness of soil, groundwater, and tracer based characterization methods may be site and technology specific. Employing multiple methods can improve characterization. The studies elucidated the importance of small-scale heterogeneities on remediation effectiveness, and fomented research on enhanced-delivery methods. Most contaminant removal occurs in hydraulically accessible zones, and complete removal is limited by contaminant mass stored in inaccessible zones. These studies illustrated the importance of understanding the fluid dynamics and interfacial behavior of injected fluids on remediation design and implementation. The importance of understanding the dynamics of NAPL-mixture dissolution and removal was highlighted. The results from these studies helped researchers better understand what processes and scales are most important to include in mathematical models used for design and data analysis. Finally, the work at these sites emphasized the importance and feasibility of recycling and reusing chemical agents, and enabled the implementation and success of follow-on full-scale efforts. © 2011 The Author(s). Ground Water © 2011 National Ground Water Association.
• McCray, J., Tick, G., Jawitz, J., Gierke, J., Brusseau, M., Falta, R., Knox, R., Sabatini, D., Annable, M., Harwell, J., & Wood, A. (2011). Remediation of NAPL Source-Zones: Lessons Learned from Field Studies at Hill and Dover AFB. Ground Water, 49, 727-744.
• Brusseau, M. L., Narter, M., & Janousek, H. (2010). Interfacial partitioning tracer test measurements of organic-liquid/water interfacial areas: Application to soils and the influence of surface roughness. Environmental Science and Technology, 44(19), 7596-7600.
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  PMID: 20825178;PMCID: PMC2957373;Abstract: Interfacial areas between an organic immiscible liquid and water were measured for two natural soils using the aqueous-phase interfacial partitioning tracer test method. The measured values were compared to measured values for silica sands compiled from the literature. The data were compared using the maximum specific interfacial area as a system index, which is useful for cases wherein fluid saturations differ. The maximum specific interfacial areas measured for the soils were significantly larger than the values obtained for the sands. The disparity between the values was attributed to the impact of surface roughness on solid surface area and hence film-associated interfacial area. A good correlation was observed between maximum specific interfacial area and specific solid surface area measured with the N2/BET method. The correlation may serve as a means by which to estimate maximum specific organic-liquid/water interfacial areas. Interfacial areas measured with the interfacial partitioning tracer method were compared to interfacial areas measured with high-resolution microtomography. Values measured with the former method were consistently larger than those measured with the latter, consistent with the general inability of the microtomography method to characterize roughness-associated surface area. © 2010 American Chemical Society.
• Brusseau, M. L., Rohay, V., & Truex, M. J. (2010). Analysis of soil vapor extraction data to evaluate mass-transfer constraints and estimate source-zone mass flux. Ground Water Monitoring and Remediation, 30(3), 57-64.
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  Abstract: Methods are developed to use data collected during cyclic operation of soil vapor extraction (SVE) systems to help characterize the magnitudes and time scales of mass flux associated with vadose zone contaminant sources. Operational data collected at the Department of Energy's Hanford site are used to illustrate the use of such data. An analysis was conducted of carbon tetrachloride vapor concentrations collected during and between SVE operations. The objective of the analysis was to evaluate changes in concentrations measured during periods of operation and nonoperation of SVE, with a focus on quantifying temporal dynamics of the vadose zone contaminant mass flux, and associated source strength. Three mass flux terms, representing mass flux during the initial period of an SVE cycle, during the asymptotic period of a cycle, and during the rebound period, were calculated and compared. It was shown that it is possible to use the data to estimate time frames for effective operation of an SVE system if a sufficient set of historical cyclic operational data exists. This information could then be used to help evaluate changes in SVE operations, including system closure. The mass flux data would also be useful for risk assessments of the impact of vadose zone sources on groundwater contamination or vapor intrusion. Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.
• Brusseau, M., DiFilippo, E. L., Carroll, K. C., & Brusseau, M. L. (2010). Impact of organic-liquid distribution and flow-field heterogeneity on reductions in mass flux. Journal of contaminant hydrology, 115(1-4).
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  A series of flow-cell experiments was conducted to investigate the impact of organic-liquid distribution and flow-field heterogeneity on the relationship between source-zone mass removal and reductions in contaminant mass flux from the source zone. Changes in source-zone architecture were quantified using image analysis, allowing explicit examination of their impact on the mass-flux-reduction/mass-removal behavior. The results showed that there was minimal reduction in mass flux until a large fraction of mass was removed for systems wherein organic liquid was present solely as residual saturation in regions that were hydraulically accessible. Conversely, significant reductions in mass flux occurred with relatively minimal mass removal for systems wherein organic liquid was present at both residual and higher saturations. The latter systems exhibited multi-step mass-flux-reduction/mass-removal behavior, and characterization of the organic-liquid saturation distribution throughout flushing allowed identification of the cause of the nonideal behavior. The age of the source zone (e.g., extent of mass removal prior to characterization) significantly influenced the observed mass-flux-reduction/mass-removal behavior. The results of this study illustrate the impact of both organic-liquid distribution and flow-field heterogeneity on mass-removal and mass-flux processes.
• Brusseau, M., Mahal, M. K., Murao, A., Johnson, G. R., Russo, A. E., & Brusseau, M. L. (2010). NONIDEAL BEHAVIOR DURING COMPLETE DISSOLUTION OF ORGANIC IMMISCIBLE LIQUID: 1. IDEAL POROUS MEDIA. Water, air, and soil pollution, 213(1-4).
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  Column experiments were conducted using ideal natural sands and stainless-steel beads to examine the complete dissolution behavior of an organic immiscible liquid. Trichloroethene (TCE) was used as the representative organic liquid. The elution curves exhibited multi-step behavior, with multiple extended periods of relatively constant contaminant flux. These secondary steady-state stages occurred at concentrations several orders-of-magnitude below aqueous solubility for the well-sorted sands. In contrast, the secondary steady-state stages occurred within one log of aqueous solubility for the poorly-sorted sand. The nonideal behavior is hypothesized to result from constraints to hydraulic accessibility of the organic liquid to flowing water, which may be expected to be mediated by the pore-scale configuration of the flow field and the fluid phases.
• Brusseau, M., Marble, J. C., Carroll, K. C., Janousek, H., & Brusseau, M. L. (2010). In situ oxidation and associated mass-flux-reduction/mass-removal behavior for systems with organic liquid located in lower-permeability sediments. Journal of contaminant hydrology, 117(1-4).
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  The effectiveness of permanganate for in situ chemical oxidation of organic liquid (trichloroethene) trapped in lower-permeability (K) zones located within a higher-permeability matrix was examined in a series of flow-cell experiments. The permanganate solution was applied in both continuous and pulsed-injection modes. Manganese-oxide precipitation, as confirmed by use of SEM-EDS, occurred within, adjacent to, and downgradient of the lower-K zones, reflective of trichloroethene oxidation. During flow interruptions, precipitate formed within the surrounding higher-permeability matrix, indicating diffusive flux of aqueous-phase trichloroethene from the lower-K zones. The impact of permanganate treatment on mass flux behavior was examined by conducting water floods after permanganate injection. The results were compared to those of water-flood control experiments. The amount of water flushing required for complete contaminant mass removal was reduced for all permanganate treatments for which complete removal was characterized. However, the nature of the mass-flux-reduction/mass-removal relationship observed during water flooding varied as a function of the specific permanganate treatment.
• Brusseau, M., Russo, A., Johnson, G. R., Schnaar, G., & Brusseau, M. L. (2010). Nonideal transport of contaminants in heterogeneous porous media: 8. Characterizing and modeling asymptotic contaminant-elution tailing for several soils and aquifer sediments. Chemosphere, 81(3).
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  Miscible-displacement experiments were conducted to characterize long-term, low-concentration elution tailing associated with sorption/desorption processes. A variety of soils and aquifer sediments, representing a range of particle-size distributions and organic-carbon contents, were employed, and trichloroethene (TCE) was used as the model organic compound. Trichloroethene transport exhibited extensive elution tailing for all media, with several hundred to several thousand pore volumes of water flushing required to reach the detection limit. The elution tailing was more extensive for the media with higher organic-carbon contents and associated retardation factors. However, when normalized by retardation, the extent of tailing did not correlate directly to organic-carbon content. These latter results suggest that differences in the geochemical nature of organic carbon (e.g., composition, structure) among the various media influenced observed behavior. A mathematical model incorporating nonlinear, rate-limited sorption/desorption described by a continuous-distribution function was used to successfully simulate trichloroethene transport, including the extensive elution tailing.
• Difilippo, E. L., Carroll, K. C., & Brusseau, M. L. (2010). Impact of organic-liquid distribution and flow-field heterogeneity on reductions in mass flux. Journal of Contaminant Hydrology, 115(1-4), 14-25.
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  PMID: 20434229;PMCID: PMC2884052;Abstract: A series of flow-cell experiments was conducted to investigate the impact of organic-liquid distribution and flow-field heterogeneity on the relationship between source-zone mass removal and reductions in contaminant mass flux from the source zone. Changes in source-zone architecture were quantified using image analysis, allowing explicit examination of their impact on the mass-flux-reduction/mass-removal behavior. The results showed that there was minimal reduction in mass flux until a large fraction of mass was removed for systems wherein organic liquid was present solely as residual saturation in regions that were hydraulically accessible. Conversely, significant reductions in mass flux occurred with relatively minimal mass removal for systems wherein organic liquid was present at both residual and higher saturations. The latter systems exhibited multi-step mass-flux-reduction/mass-removal behavior, and characterization of the organic-liquid saturation distribution throughout flushing allowed identification of the cause of the nonideal behavior. The age of the source zone (e.g., extent of mass removal prior to characterization) significantly influenced the observed mass-flux-reduction/mass-removal behavior. The results of this study illustrate the impact of both organic-liquid distribution and flow-field heterogeneity on mass-removal and mass-flux processes. © 2010 Elsevier B.V. All rights reserved.
• Mahal, M. K., Murao, A., Johnson, G. R., Russo, A. E., & Brusseau, M. L. (2010). Non-ideal behavior during complete dissolution of organic immiscible liquid: 2. Ideal porous media. Water, Air, and Soil Pollution, 213(1-4), 191-197.
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  Abstract: Column experiments were conducted using ideal natural sands and stainless-steel beads to examine the complete dissolution behavior of an organic immiscible liquid. Trichloroethene was used as the representative organic liquid. The elution curves exhibited multi-step behavior, with multiple extended periods of relatively constant contaminant flux. These secondary steady-state stages occurred at concentrations several orders-of-magnitude below aqueous solubility for the well-sorted sands. In contrast, the secondary steady-state stages occurred within 1 log of aqueous solubility for the poorly sorted sand. The non-ideal behavior is hypothesized to result from constraints to hydraulic accessibility of the organic liquid to flowing water, which may be expected to be mediated by the pore-scale configuration of the flow field and the fluid phases. © 2010 Springer Science+Business Media B.V.
• Marble, J. C., Carroll, K. C., Janousek, H., & Brusseau, M. L. (2010). In situ oxidation and associated mass-flux-reduction/mass-removal behavior for systems with organic liquid located in lower-permeability sediments. Journal of Contaminant Hydrology, 117(1-4), 82-93.
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  PMID: 20685008;PMCID: PMC2957374;Abstract: The effectiveness of permanganate for in situ chemical oxidation of organic liquid (trichloroethene) trapped in lower-permeability (K) zones located within a higher-permeability matrix was examined in a series of flow-cell experiments. The permanganate solution was applied in both continuous and pulsed-injection modes. Manganese-oxide precipitation, as confirmed by use of SEM-EDS, occurred within, adjacent to, and downgradient of the lower-K zones, reflective of trichloroethene oxidation. During flow interruptions, precipitate formed within the surrounding higher-permeability matrix, indicating diffusive flux of aqueous-phase trichloroethene from the lower-K zones. The impact of permanganate treatment on mass flux behavior was examined by conducting water floods after permanganate injection. The results were compared to those of water-flood control experiments. The amount of water flushing required for complete contaminant mass removal was reduced for all permanganate treatments for which complete removal was characterized. However, the nature of the mass-flux-reduction/mass-removal relationship observed during water flooding varied as a function of the specific permanganate treatment. Copyright © 2010 Published by Elsevier B.V. All rights reserved.
• Narter, M., & Brusseau, M. L. (2010). Comparison of interfacial partitioning tracer test and high-resolution microtomography measurements of fluid-fluid interfacial areas for an ideal porous medium. Water Resources Research, 46(8).
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  Abstract: Fluid-fluid interfacial area for porous media systems can be measured with the aqueous phase interfacial partitioning tracer test (IPTT) method or with high-resolution microtomography. The results of prior studies have shown that interfacial areas measured with the IPTT method are larger than values measured with microtomography. The observed disparity has been hypothesized to result from the impact of porous medium surface roughness on film-associated interfacial area, wherein the influence of surface roughness is characterized to some extent by the IPTT method but not by microtomography due to resolution constraints. This hypothesis was tested by using the two methods to measure interfacial area between an organic immiscible liquid and water for an ideal glass beads medium that has no measurable surface roughness. The tracer tests yielded a mean interfacial area of 2.8 (5 cm-1), while microtomography produced an interfacial area of 2.7 (2 cm-1). Maximum specific interfacial areas, equivalent to areas normalized by nonwetting fluid volume, were calculated and compared to measures of the specific solid surface area. The normalized interfacial areas were similar to the specific solid surface area calculated using the smooth sphere assumption and to the specific solid surface area measured using the N2/Brunauer, Emmett, and Teller (BET) method. The results presented herein indicate that both the IPTT and microtomography methods provide robust characterization of fluid-fluid interfacial area and that they are comparable in the absence of the impact of surface roughness. Copyright © 2010 by the American Geophysical Union.
• Russo, A., Johnson, G. R., Schnaar, G., & Brusseau, M. L. (2010). Nonideal transport of contaminants in heterogeneous porous media: 8. Characterizing and modeling asymptotic contaminant-elution tailing for several soils and aquifer sediments. Chemosphere, 81(3), 366-371.
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  PMID: 20692012;PMCID: PMC2939749;Abstract: Miscible-displacement experiments were conducted to characterize long-term, low-concentration elution tailing associated with sorption/desorption processes. A variety of soils and aquifer sediments, representing a range of particle-size distributions and organic-carbon contents, were employed, and trichloroethene (TCE) was used as the model organic compound. Trichloroethene transport exhibited extensive elution tailing for all media, with several hundred to several thousand pore volumes of water flushing required to reach the detection limit. The elution tailing was more extensive for the media with higher organic-carbon contents and associated retardation factors. However, when normalized by retardation, the extent of tailing did not correlate directly to organic-carbon content. These latter results suggest that differences in the geochemical nature of organic carbon (e.g., composition, structure) among the various media influenced observed behavior. A mathematical model incorporating nonlinear, rate-limited sorption/desorption described by a continuous-distribution function was used to successfully simulate trichloroethene transport, including the extensive elution tailing. © 2010 Elsevier Ltd.
• Werth, C. J., Zhang, C., Brusseau, M. L., Oostrom, M., & Baumann, T. (2010). A review of non-invasive imaging methods and applications in contaminant hydrogeology research. Journal of Contaminant Hydrology, 113(1-4), 1-24.
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  PMID: 20163885;PMCID: PMC3864598;Abstract: Contaminant hydrogeological processes occurring in porous media are typically not amenable to direct observation. As a result, indirect measurements (e.g., contaminant breakthrough at a fixed location) are often used to infer processes occurring at different scales, locations, or times. To overcome this limitation, non-invasive imaging methods are increasingly being used in contaminant hydrogeology research. Four of the most common methods, and the subjects of this review, are optical imaging using UV or visible light, dual-energy gamma radiation, X-ray microtomography, and magnetic resonance imaging (MRI). Non-invasive imaging techniques have provided valuable insights into a variety of complex systems and processes, including porous media characterization, multiphase fluid distribution, fluid flow, solute transport and mixing, colloidal transport and deposition, and reactions. In this paper we review the theory underlying these methods, applications of these methods to contaminant hydrogeology research, and methods' advantages and disadvantages. As expected, there is no perfect method or tool for non-invasive imaging. However, optical methods generally present the least expensive and easiest options for imaging fluid distribution, solute and fluid flow, colloid transport, and reactions in artificial two-dimensional (2D) porous media. Gamma radiation methods present the best opportunity for characterization of fluid distributions in 2D at the Darcy scale. X-ray methods present the highest resolution and flexibility for three-dimensional (3D) natural porous media characterization, and 3D characterization of fluid distributions in natural porous media. And MRI presents the best option for 3D characterization of fluid distribution, fluid flow, colloid transport, and reaction in artificial porous media. Obvious deficiencies ripe for method development are the ability to image transient processes such as fluid flow and colloid transport in natural porous media in three dimensions, the ability to image many reactions of environmental interest in artificial and natural porous media, and the ability to image selected processes over a range of scales in artificial and natural porous media. © 2010.
• Brusseau, M. L., Narter, M., Schnaar, G., & Marble, J. (2009). Measurement and estimation of organic-liquid/water interfacial areas for several natural porous media. Environmental Science and Technology, 43(10), 3619-3625.
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  PMID: 19544863;PMCID: PMC3167572;Abstract: The objective of this study was to quantitatively characterize the impact of porous-medium texture on interfacial area between immiscible organic liquid and water residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of solid and liquid phases in packed columns. The image data were processed to generate quantitative measurements of organic-liquid/water interfacial area and of organic-liquid blob sizes. Ten porous media, comprising a range of median grain sizes, grain-size distributions, and geochemical properties, were used to evaluate the impact of porous-medium texture on interfacial area. The results show that fluid-normalized specific interfacial area (Af) and maximum specific interfacial area (Am) correlate very well to inverse median grain diameter. These functionalities were shown to result from a linear relationship between effective organic-liquid blob diameter and median grain diameter. These results provide the basis for a simple method for estimating specific organic-liquid/water interfacial area as a function of fluid saturation for a given porous medium. The availability of a method for which the only parameter needed is the simple-to-measure median grain diameter should be of great utility for a variety of applications. © 2009 American Chemical Society.
• Brusseau, M., Carroll, K. C., & Brusseau, M. L. (2009). Dissolution, cyclodextrin-enhanced solubilization, and mass removal of an ideal multicomponent organic liquid. Journal of contaminant hydrology, 106(1-2).
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  Laboratory experiments and mathematical modeling were conducted to examine the influence of a hydroxypropyl-beta-cyclodextrin (HPCD) solution on the dissolution of single- and three-component organic liquids. The results of batch experiments showed that HPCD-enhanced solubilization of the organic-liquid mixtures was ideal (describable using Raoult's Law), and that solubilization-enhancement factors were independent of mixture composition. Addition of the HPCD solution to columns containing residual saturations of the organic liquid enhanced the dissolution and removal of all three compounds in the mixture. The results of the column experiments and mathematical modeling suggest that solubilization was ideal for both water and cyclodextrin flushing. Concomitantly, the mass-flux reduction versus mass removal behavior was ideal for all experiments. Mass transfer was increased for HPCD solubilization relative to the water flushing due to solubility and concentration-gradient enhancement. Organic-liquid composition did not significantly impact mass transfer coefficients, and fractional mass removal behavior during HPCD solubilization was nearly identical for each compound whether present as a single component or in a mixture. Additionally, mass transfer coefficients for aqueous and HPCD solubilization for single and multicomponent mixtures were not statistically different upon normalizing by the solubility enhancement factor.
• Brusseau, M., Carroll, K. C., Taylor, R., Gray, E., & Brusseau, M. L. (2009). The impact of composition on the physical properties and evaporative mass transfer of a PCE-diesel immiscible liquid. Journal of hazardous materials, 164(2-3).
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  The impact of immiscible-liquid composition on mass transfer between immiscible liquid and vapor phases was evaluated for a complex mixture of chlorinated solvents and petroleum hydrocarbons. A mixture of tetrachloroethene and diesel was discovered at a site in Tucson, Arizona. Partitioning of tetrachloroethene into a layer of diesel has been observed, with resultant concentrations of tetrachloroethene up to approximately 15% by weight. The density, viscosity, surface tension, and interfacial tension were measured for tetrachloroethene-diesel mixtures with tetrachloroethene fractions ranging from 7% to 32%, and the results indicated that immiscible-liquid composition did impact the physical properties of the tetrachloroethene-diesel mixture. The results of batch phase-partitioning experiments were compared to predictions based on Raoult's Law, and the analysis indicated that immiscible-liquid/vapor and immiscible-liquid/water partitioning were both essentially ideal. Flow-cell experiments were conducted to characterize steady-state tetrachloroethene removal from the tetrachloroethene-diesel mixture via vapor extraction. The effluent concentrations for the experiment conducted with free-phase immiscible liquid were comparable to equilibrium values. Conversely, the effluent concentrations were significantly lower for the experiment wherein a residual saturation of immiscible liquid was distributed within sand. The lower concentrations for the latter experiment were attributed to dilution effects associated with a nonuniform distribution of immiscible liquid within the flow cell.
• Brusseau, M., Kempf, A., & Brusseau, M. L. (2009). Impact of non-ideal sorption on low-concentration tailing behavior for atrazine transport in two natural porous media. Chemosphere, 77(6).
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  The impact of non-ideal sorption on atrazine transport was investigated for two sandy porous media with 0.38% and 0.03% organic-carbon contents. In contrast to prior investigations, effluent atrazine concentrations were monitored over a range of five orders of magnitude to examine long-term elution behavior. As characterized by batch-experiments, atrazine experienced nonlinear sorption for both media. The results of the column experiments showed that atrazine exhibited extensive elution tailing (delayed approach to relative concentration of zero). This non-ideal transport was more pronounced for the medium with higher organic-carbon content. A mathematical model incorporating nonlinear, rate-limited sorption/desorption described by a continuous-distribution function was used to successfully simulate atrazine transport.
• Brusseau, M., Russo, A. E., Mahal, M. K., & Brusseau, M. L. (2009). Nonideal behavior during complete dissolution of organic immiscible liquid: 1. Natural porous media. Journal of hazardous materials, 172(1).
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  Experiments were conducted to investigate the complete dissolution of organic immiscible liquid residing within natural porous media. Organic-liquid dissolution was investigated by conducting experiments with homogeneously packed columns containing a residual saturation of organic liquid (trichloroethene). The porous media used comprised different textures (ranges of particle-size distributions) and organic-carbon contents. The dissolution behavior that was observed for the soil and aquifer sediment systems deviated from the behavior typically observed for systems composed of ideal sands. Specifically, multi-step elution curves were observed, with multiple extended periods of relatively constant contaminant flux. This behavior was more pronounced for the two media with larger particle-size distributions. Conversely, this type of dissolution behavior was not observed for the control system, which consisted of a well-sorted sand. It is hypothesized that the pore-scale configuration of the organic liquid and of the flow field is more complex for the poorly sorted media, and that this greater complexity constrains dissolution dynamics, leading to the observed nonideal behavior.
• Brusseau, M., Russo, A. E., Narter, M., & Brusseau, M. L. (2009). Characterizing pore-scale dissolution of organic immiscible liquid in a poorly-sorted natural porous medium. Environmental science & technology, 43(15).
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  Synchrotron X-ray microtomography was used to characterize the pore-scale morphology and distribution of an organic immiscible liquid (trichloroethene) during water flushing to examine dissolution dynamics. The experiments were conducted with a natural porous medium that has a large particle-size distribution. The results were compared to those of a previous experiment conducted with a well-sorted natural sand. The median organic-liquid blob volume was smaller, and smaller blobs composed a larger fraction of the distribution, for the poorly sorted medium. In addition, mass removal was less spatially uniform for the poorly sorted medium. The concentration of trichloroethene in the column effluent was monitored during dissolution to assess mass-flux behavior. A first-order mass transfer equation was used to simulate the measured elution curves. Organic-liquid/water interfacial areas measured with microtomography were used as input, and simulated effluent concentrations were compared to the measured effluent concentrations to determine best-fit values for the mass-transfer coefficient. The value obtained for the poorly sorted medium was approximately 10 times smaller than that obtained for the well-sorted medium. This disparity indicates that hydraulic accessibility of the organic liquid is more constrained for the poorly sorted medium, which would be consistent with a more complex pore-scale flow field for the poorly sorted medium.
• Carroll, K. C., & Brusseau, M. L. (2009). Dissolution, cyclodextrin-enhanced solubilization, and mass removal of an ideal multicomponent organic liquid. Journal of Contaminant Hydrology, 106(1-2), 62-72.
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  PMID: 19233508;PMCID: PMC2867052;Abstract: Laboratory experiments and mathematical modeling were conducted to examine the influence of a hydroxypropyl-beta-cyclodextrin (HPCD) solution on the dissolution of single- and three-component organic liquids. The results of batch experiments showed that HPCD-enhanced solubilization of the organic-liquid mixtures was ideal (describable using Raoult's Law), and that solubilization-enhancement factors were independent of mixture composition. Addition of the HPCD solution to columns containing residual saturations of the organic liquid enhanced the dissolution and removal of all three compounds in the mixture. The results of the column experiments and mathematical modeling suggest that solubilization was ideal for both water and cyclodextrin flushing. Concomitantly, the mass-flux reduction versus mass removal behavior was ideal for all experiments. Mass transfer was increased for HPCD solubilization relative to the water flushing due to solubility and concentration-gradient enhancement. Organic-liquid composition did not significantly impact mass transfer coefficients, and fractional mass removal behavior during HPCD solubilization was nearly identical for each compound whether present as a single component or in a mixture. Additionally, mass transfer coefficients for aqueous and HPCD solubilization for single and multicomponent mixtures were not statistically different upon normalizing by the solubility enhancement factor. © 2009 Elsevier B.V. All rights reserved.
• Carroll, K. C., Taylor, R., Gray, E., & Brusseau, M. L. (2009). The impact of composition on the physical properties and evaporative mass transfer of a PCE-diesel immiscible liquid. Journal of Hazardous Materials, 164(2-3), 1074-1081.
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  PMID: 18926630;PMCID: PMC2864079;Abstract: The impact of immiscible-liquid composition on mass transfer between immiscible liquid and vapor phases was evaluated for a complex mixture of chlorinated solvents and petroleum hydrocarbons. A mixture of tetrachloroethene and diesel was discovered at a site in Tucson, Arizona. Partitioning of tetrachloroethene into a layer of diesel has been observed, with resultant concentrations of tetrachloroethene up to approximately 15% by weight. The density, viscosity, surface tension, and interfacial tension were measured for tetrachloroethene-diesel mixtures with tetrachloroethene fractions ranging from 7% to 32%, and the results indicated that immiscible-liquid composition did impact the physical properties of the tetrachloroethene-diesel mixture. The results of batch phase-partitioning experiments were compared to predictions based on Raoult's Law, and the analysis indicated that immiscible-liquid/vapor and immiscible-liquid/water partitioning were both essentially ideal. Flow-cell experiments were conducted to characterize steady-state tetrachloroethene removal from the tetrachloroethene-diesel mixture via vapor extraction. The effluent concentrations for the experiment conducted with free-phase immiscible liquid were comparable to equilibrium values. Conversely, the effluent concentrations were significantly lower for the experiment wherein a residual saturation of immiscible liquid was distributed within sand. The lower concentrations for the latter experiment were attributed to dilution effects associated with a nonuniform distribution of immiscible liquid within the flow cell. © 2008 Elsevier B.V. All rights reserved.
• Johnson, G. R., Norris, D. K., & Brusseau, M. L. (2009). Mass removal and low-concentration tailing of trichloroethene in freshly-amended, synthetically-aged, and field-contaminated aquifer material. Chemosphere, 75(4), 542-548.
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  PMID: 19157496;PMCID: PMC2898734;Abstract: This study investigates the effect of contaminant aging on the sorption/desorption and transport of trichloroethene in a low organic-carbon content aquifer material, comparing mass removal and long-term, low-concentration elution tailing for field-contaminated, synthetically-aged (contact times of approximately four years), and freshly-amended aquifer material. Elution of trichloroethene exhibited extensive low-concentration tailing, despite minimal retention of trichloroethene by the aquifer material. The observed nonideal transport behavior of trichloroethene is attributed primarily to rate-limited sorption/desorption, with a smaller contribution from nonlinear sorption. It is hypothesized that interaction with physically condensed carbonaceous material, comprising 61% of the aquifer material's organic-carbon content, mediates the retention behavior of trichloroethene. The elution behavior of trichloroethene for the field-contaminated and aged treatments was essentially identical to that observed for the fresh treatments. In addition, the results of three independent mass-balance analyses, total mass eluted, solvent-extraction analysis of residual sorbed mass, and aqueous-phase concentration rebounds following stop-flow experiments, showed equivalent recoveries for the aged and fresh treatments. These results indicate that long-term contaminant aging did not significantly influence the retention and transport of trichloroethene in this low organic-carbon aquifer material. © 2008 Elsevier Ltd. All rights reserved.
• Kempf, A., & Brusseau, M. L. (2009). Impact of non-ideal sorption on low-concentration tailing behavior for atrazine transport in two natural porous media. Chemosphere, 77(6), 877-882.
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  PMID: 19699507;PMCID: PMC3165047;Abstract: The impact of non-ideal sorption on atrazine transport was investigated for two sandy porous media with 0.38% and 0.03% organic-carbon contents. In contrast to prior investigations, effluent atrazine concentrations were monitored over a range of five orders of magnitude to examine long-term elution behavior. As characterized by batch-experiments, atrazine experienced nonlinear sorption for both media. The results of the column experiments showed that atrazine exhibited extensive elution tailing (delayed approach to relative concentration of zero). This non-ideal transport was more pronounced for the medium with higher organic-carbon content. A mathematical model incorporating nonlinear, rate-limited sorption/desorption described by a continuous-distribution function was used to successfully simulate atrazine transport. © 2009 Elsevier Ltd. All rights reserved.
• Russo, A. E., Mahal, M. K., & Brusseau, M. L. (2009). Nonideal behavior during complete dissolution of organic immiscible liquid. 1. Natural porous media. Journal of Hazardous Materials, 172(1), 208-213.
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  PMID: 19643542;PMCID: PMC3167578;Abstract: Experiments were conducted to investigate the complete dissolution of organic immiscible liquid residing within natural porous media. Organic-liquid dissolution was investigated by conducting experiments with homogeneously packed columns containing a residual saturation of organic liquid (trichloroethene). The porous media used comprised different textures (ranges of particle-size distributions) and organic-carbon contents. The dissolution behavior that was observed for the soil and aquifer sediment systems deviated from the behavior typically observed for systems composed of ideal sands. Specifically, multi-step elution curves were observed, with multiple extended periods of relatively constant contaminant flux. This behavior was more pronounced for the two media with larger particle-size distributions. Conversely, this type of dissolution behavior was not observed for the control system, which consisted of a well-sorted sand. It is hypothesized that the pore-scale configuration of the organic liquid and of the flow field is more complex for the poorly sorted media, and that this greater complexity constrains dissolution dynamics, leading to the observed nonideal behavior. © 2009 Elsevier B.V. All rights reserved.
• Russo, A. E., Narter, M., & Brusseau, M. L. (2009). Characterizing pore-scale dissolution of organic immiscible liquid in a poorly-sorted natural porous medium. Environmental Science and Technology, 43(15), 5671-5678.
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  PMID: 19731661;PMCID: PMC3165041;Abstract: Synchrotron X-ray microtomography was used to characterize the pore-scale morphology and distribution of an organic immiscible liquid (trichloroethene) during water flushing to examine dissolution dynamics. The experiments were conducted with a natural porous medium that has a large particle-size distribution. The results were compared to those of a previous experiment conducted with a well-sorted natural sand. The median organic-liquid blob volume was smaller, and smaller blobs composed a larger fraction of the distribution, for the poorly sorted medium. In addition, mass removal was less spatially uniform for the poorly sorted medium. The concentration of trichloroethene in the column effluent was monitored during dissolution to assess mass-flux behavior. A first-order mass transfer equation was used to simulate the measured elution curves. Organic-liquid/water interfacial areas measured with microtomography were used as input, and simulated effluent concentrations were compared to the measured effluent concentrations to determine best-fit values for the masstransfer coefficient. The value obtained for the poorly sorted medium was approximately 10 times smaller than that obtained for the well-sorted medium. This disparity indicates that hydraulic accessibility of the organic liquid is more constrained for the poorly sorted medium, which would be consistent with a more complex pore-scale flow field for the poorly sorted medium. © 2009 American Chemical Society.
• Truex, M. J., Oostrom, M., & Brusseau, M. L. (2009). Estimating persistent mass flux of volatile contaminants from the vadose zone to ground water. Ground Water Monitoring and Remediation, 29(2), 63-72.
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  Abstract: Contaminants may persist for long time periods within low permeability portions of the vadose zone where they cannot be effectively treated and are a potential continuing source of contamination to ground water. Setting appropriate vadose zone remediation goals typically requires evaluating these persistent sources in terms of their impact on meeting ground water remediation goals. Estimating the impact on ground water can be challenging at sites with low aqueous recharge rates where vapor-phase movement is the dominant transport process in the vadose zone. Existing one-dimensional approaches for simulating transport of volatile contaminants in the vadose zone are considered and compared to a new flux-continuity-based assessment of vapor-phase contaminant movement from the vadose zone to the ground water. The flux-continuity-based assessment demonstrates that the ability of the ground water to move contaminant away from the water table controls the vapor-phase mass flux from the vadose zone across the water table. Limitations of these approaches are then discussed with respect to the required assumptions and the need to incorporate three-dimensional processes when evaluating vapor-phase transport from the vadose zone to the ground water. The carbon tetrachloride plume at the U.S. Department of Energy Hanford Site is used as the example site where persistent vadose zone contamination needs to be considered in the context of ground water remediation. © 2009 National Ground Water Association.
• Boving, T. B., Blanford, W. J., McCray, J. E., Divine, C. E., & Brusseau, M. L. (2008). Comparison of line-drive and push-pull flushing schemes. Ground Water Monitoring and Remediation, 28(1), 75-86.
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  Abstract: The performance of cyclodextrin (CD)-enhanced push-pull (PP) and line-drive (LD) approaches to remediation of a site contaminated with a multicomponent dense nonaqueous phase liquid (DNAPL) present in a surficial sandy aquifer was evaluated in this field study. The treatment techniques were compared to each other and to the projected performance of a conventional water-flushing system. Performance was assessed based on contaminant mass removed per unit volume of extraction solution and per unit time of operation. As expected, the CD-enhanced LD and PP approaches to remediation were more efficient than conventional flushing with water. Between the two techniques, the PP approach performed 1.5 to 2 times better than the LD approach, particularly for higher DNAPL saturation of the source zone. This result suggests that forcing the flushing solution directly into and through the DNAPL source zone minimized flow bypassing and consequently resulted in a more efficient transfer of contaminant mass between the DNAPL phase and the flushing solution. Nonuniform treatment zone contaminant concentrations and changes in contaminant composition influenced the treatment performances, but these effects were small and still permitted the comparison of successive tests. Although CD was used as the solubility-enhancing flushing agent in this study, it is likely that the results can be transferred to other chemically enhanced flushing technologies that use, for example, surfactants or alcohols. © 2008 The Author(s).
• Brusseau, M. L., DiFilippo, E. L., Marble, J. C., & Oostrom, M. (2008). Mass-removal and mass-flux-reduction behavior for idealized source zones with hydraulically poorly-accessible immiscible liquid. Chemosphere, 71(8), 1511-1521.
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  PMID: 18279910;PMCID: PMC2864070;Abstract: A series of flow-cell experiments was conducted to investigate aqueous dissolution and mass-removal behavior for systems wherein immiscible liquid was non-uniformly distributed in physically heterogeneous source zones. The study focused specifically on characterizing the relationship between mass flux reduction and mass removal for systems for which immiscible liquid is poorly accessible to flowing water. Two idealized scenarios were examined, one wherein immiscible liquid at residual saturation exists within a lower-permeability unit residing in a higher-permeability matrix, and one wherein immiscible liquid at higher saturation (a pool) exists within a higher-permeability unit adjacent to a lower-permeability unit. The results showed that significant reductions in mass flux occurred at relatively moderate mass-removal fractions for all systems. Conversely, minimal mass flux reduction occurred until a relatively large fraction of mass (>80%) was removed for the control experiment, which was designed to exhibit ideal mass removal. In general, mass flux reduction was observed to follow an approximately one-to-one relationship with mass removal. Two methods for estimating mass-flux-reduction/mass-removal behavior, one based on system-indicator parameters (ganglia-to-pool ratio) and the other a simple mass-removal function, were used to evaluate the measured data. The results of this study illustrate the impact of poorly accessible immiscible liquid on mass-removal and mass-flux processes, and the difficulties posed for estimating mass-flux-reduction/mass-removal behavior. © 2007 Elsevier Ltd. All rights reserved.
• Brusseau, M. L., Janousek, H., Murao, A., & Schnaar, G. (2008). Synchrotron X-ray microtomography and interfacial partitioning tracer test measurements of NAPL-water interfacial areas. Water Resources Research, 44(1).
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  Abstract: Interfacial areas between an immiscible organic liquid (NAPL), and water were measured for two natural porous media using two methods, aqueous-phase interfacial partitioning tracer tests and synchrotron X-ray microtomography. The interfacial areas measured with the tracer tests were similar to previously reported values obtained with the method. The values were, however, significantly larger than those obtained from microtomography. Analysis of microtomography data collected before and after introduction of the interfacial tracer solution indicated that the surfactant tracer had minimal impact on fluid-phase configuration and interfacial areas under conditions associated with typical laboratory application. The disparity between the tracer test and microtomography values is attributed primarily to the inability of the microtomography method to resolve interfacial area associated with microscopic surface heterogeneity. This hypothesis is consistent with results recently reported for a comparison of microtomographic analysis and interfacial tracer tests conducted for an air-water system. The tracer test method provides a measure of effective, total (capillary and film) interfacial area, whereas microtomography can be used to determine separately both capillary-associated and film-associated interfacial areas. Both methods appear to provide useful information for given applications. A key to their effective use is recognizing the specific nature of the information provided by each, as well as associated limitations. Copyright 2008 by the American Geophysical Union.
• Brusseau, M., Difilippo, E. L., & Brusseau, M. L. (2008). Relationship between mass-flux reduction and source-zone mass removal: analysis of field data. Journal of contaminant hydrology, 98(1-2).
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  The magnitude of contaminant mass-flux reduction associated with a specific amount of contaminant mass removed is a key consideration for evaluating the effectiveness of a source-zone remediation effort. Thus, there is great interest in characterizing, estimating, and predicting relationships between mass-flux reduction and mass removal. Published data collected for several field studies were examined to evaluate relationships between mass-flux reduction and source-zone mass removal. The studies analyzed herein represent a variety of source-zone architectures, immiscible-liquid compositions, and implemented remediation technologies. There are two general approaches to characterizing the mass-flux-reduction/mass-removal relationship, end-point analysis and time-continuous analysis. End-point analysis, based on comparing masses and mass fluxes measured before and after a source-zone remediation effort, was conducted for 21 remediation projects. Mass removals were greater than 60% for all but three of the studies. Mass-flux reductions ranging from slightly less than to slightly greater than one-to-one were observed for the majority of the sites. However, these single-snapshot characterizations are limited in that the antecedent behavior is indeterminate. Time-continuous analysis, based on continuous monitoring of mass removal and mass flux, was performed for two sites, both for which data were obtained under water-flushing conditions. The reductions in mass flux were significantly different for the two sites (90% vs. approximately 8%) for similar mass removals ( approximately 40%). These results illustrate the dependence of the mass-flux-reduction/mass-removal relationship on source-zone architecture and associated mass-transfer processes. Minimal mass-flux reduction was observed for a system wherein mass removal was relatively efficient (ideal mass-transfer and displacement). Conversely, a significant degree of mass-flux reduction was observed for a site wherein mass removal was inefficient (non-ideal mass-transfer and displacement). The mass-flux-reduction/mass-removal relationship for the latter site exhibited a multi-step behavior, which cannot be predicted using some of the available simple estimation functions.
• Brusseau, M., Marble, J. C., DiFilippo, E. L., Zhang, Z., Tick, G. R., & Brusseau, M. L. (2008). Application of a lumped-process mathematical model to dissolution of non-uniformly distributed immiscible liquid in heterogeneous porous media. Journal of contaminant hydrology, 100(1-2).
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  The use of a lumped-process mathematical model to simulate the complete dissolution of immiscible liquid non-uniformly distributed in physically heterogeneous porous-media systems was investigated. The study focused specifically on systems wherein immiscible liquid was poorly accessible to flowing water. Two representative, idealized scenarios were examined, one wherein immiscible liquid at residual saturation exists within a lower-permeability unit residing in a higher-permeability matrix, and one wherein immiscible liquid at higher saturation (a pool) exists within a higher-permeability unit adjacent to a lower-permeability unit. As expected, effluent concentrations were significantly less than aqueous solubility due to dilution and by-pass flow effects. The measured data were simulated with two mathematical models, one based on a simple description of the system and one based on a more complex description. The permeability field and the distribution of the immiscible-liquid zones were represented explicitly in the more complex, distributed-process model. The dissolution rate coefficient in this case represents only the impact of local-scale (and smaller) processes on dissolution, and the parameter values were accordingly obtained from the results of experiments conducted with one-dimensional, homogeneously-packed columns. In contrast, the system was conceptualized as a pseudo-homogeneous medium with immiscible liquid uniformly distributed throughout the system for the simpler, lumped-process model. With this approach, all factors that influence immiscible-liquid dissolution are incorporated into the calibrated dissolution rate coefficient, which in such cases serves as a composite or lumped term. The calibrated dissolution rate coefficients obtained from the simulations conducted with the lumped-process model were approximately two to three orders-of-magnitude smaller than the independently-determined values used for the simulations conducted with the distributed-process model. This disparity reflects the difference in implicit versus explicit consideration of the larger-scale factors influencing immiscible-liquid dissolution in the systems.
• Brusseau, M., McColl, C. M., Johnson, G. R., & Brusseau, M. L. (2008). Evaporative mass transfer behavior of a complex immiscible liquid. Chemosphere, 73(4).
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  A series of laboratory experiments was conducted with a multiple-component immiscible liquid, collected from the Picillo Farm Superfund Site in Rhode Island, to examine liquid-vapor mass-transfer behavior. The immiscible liquid, which comprises solvents, oils, pesticides, PCBs, paint sludges, explosives, and other compounds, was characterized using gas chromatography and gas chromatography/mass spectrometry to determine mole fractions of selected constituents. Batch experiments were conducted to evaluate equilibrium phase-partitioning behavior. Two sets of air-stripping column studies were conducted to examine the mass-transfer dynamics of five selected target compounds present in the immiscible-liquid mixture. One set of column experiments was designed to represent a system with free-phase immiscible liquid present; the other was designed to represent a system with a residual phase of immiscible liquid. Initial elution behavior of all target components generally appeared to be ideal for both systems, as the initial vapor-phase concentrations were similar to vapor-phase concentrations measured for the batch experiment and those estimated using Raoult's law (incorporating the immiscible-liquid composition data). Later-stage removal of 1,2-dichlorobenzene appeared to be rate limited for the columns containing free-phase immiscible liquid and no porous medium. Conversely, evaporative mass transfer appeared to be ideal throughout the experiment conducted with immiscible liquid distributed relatively uniformly as a residual phase within a sandy porous medium.
• Chorover, J., & Brusseau, M. L. (2008). Kinetics of sorption-desorption. Kinetics of Water-Rock Interaction, 109-149.
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  Abstract: The fate of nutrients, pollutants and other solutes in natural waters is coupled to their distribution between solid, aqueous and gas phases. The processes of phase distribution are many, including penetration and absorption into one of the phases, or accumulation at the interface between them. The term sorption is defined here as the full range of processes whereby matter is partitioned between the gas, aqueous and solid phases. In geochemical systems, this includes adsorption of matter at the surfaces of solid particles (minerals and organic matter) or at the air-water interface, and absorption into the solids during surface precipitation or solid phase diffusion. The complexity of natural geomedia (Fig. 4.1) implies that both broad classes of sorption reaction may occur simultaneously. As discussed in this chapter, recent research into the kinetics and mechanisms of sorption for inorganic and organic species indicates that both processes are indeed important. The relative predominance of a given reaction and sorbate-sorbent structure is a function of time scale, system loading and geochemical conditions. © 2008 Springer New York.
• DiFilippo, E. L., & Brusseau, M. L. (2008). Relationship between mass-flux reduction and source-zone mass removal: Analysis of field data. Journal of Contaminant Hydrology, 98(1-2), 22-35.
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  PMID: 18407371;PMCID: PMC3029099;Abstract: The magnitude of contaminant mass-flux reduction associated with a specific amount of contaminant mass removed is a key consideration for evaluating the effectiveness of a source-zone remediation effort. Thus, there is great interest in characterizing, estimating, and predicting relationships between mass-flux reduction and mass removal. Published data collected for several field studies were examined to evaluate relationships between mass-flux reduction and source-zone mass removal. The studies analyzed herein represent a variety of source-zone architectures, immiscible-liquid compositions, and implemented remediation technologies. There are two general approaches to characterizing the mass-flux-reduction/mass-removal relationship, end-point analysis and time-continuous analysis. End-point analysis, based on comparing masses and mass fluxes measured before and after a source-zone remediation effort, was conducted for 21 remediation projects. Mass removals were greater than 60% for all but three of the studies. Mass-flux reductions ranging from slightly less than to slightly greater than one-to-one were observed for the majority of the sites. However, these single-snapshot characterizations are limited in that the antecedent behavior is indeterminate. Time-continuous analysis, based on continuous monitoring of mass removal and mass flux, was performed for two sites, both for which data were obtained under water-flushing conditions. The reductions in mass flux were significantly different for the two sites (90% vs. ∼ 8%) for similar mass removals (∼ 40%). These results illustrate the dependence of the mass-flux-reduction/mass-removal relationship on source-zone architecture and associated mass-transfer processes. Minimal mass-flux reduction was observed for a system wherein mass removal was relatively efficient (ideal mass-transfer and displacement). Conversely, a significant degree of mass-flux reduction was observed for a site wherein mass removal was inefficient (non-ideal mass-transfer and displacement). The mass-flux-reduction/mass-removal relationship for the latter site exhibited a multi-step behavior, which cannot be predicted using some of the available simple estimation functions. © 2008 Elsevier B.V. All rights reserved.
• Marble, J. C., DiFilippo, E. L., Zhang, Z., Tick, G. R., & Brusseau, M. L. (2008). Application of a lumped-process mathematical model to dissolution of non-uniformly distributed immiscible liquid in heterogeneous porous media. Journal of Contaminant Hydrology, 100(1-2), 1-10.
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  PMID: 18555558;PMCID: PMC2864080;Abstract: The use of a lumped-process mathematical model to simulate the complete dissolution of immiscible liquid non-uniformly distributed in physically heterogeneous porous-media systems was investigated. The study focused specifically on systems wherein immiscible liquid was poorly accessible to flowing water. Two representative, idealized scenarios were examined, one wherein immiscible liquid at residual saturation exists within a lower-permeability unit residing in a higher-permeability matrix, and one wherein immiscible liquid at higher saturation (a pool) exists within a higher-permeability unit adjacent to a lower-permeability unit. As expected, effluent concentrations were significantly less than aqueous solubility due to dilution and by-pass flow effects. The measured data were simulated with two mathematical models, one based on a simple description of the system and one based on a more complex description. The permeability field and the distribution of the immiscible-liquid zones were represented explicitly in the more complex, distributed-process model. The dissolution rate coefficient in this case represents only the impact of local-scale (and smaller) processes on dissolution, and the parameter values were accordingly obtained from the results of experiments conducted with one-dimensional, homogeneously-packed columns. In contrast, the system was conceptualized as a pseudo-homogeneous medium with immiscible liquid uniformly distributed throughout the system for the simpler, lumped-process model. With this approach, all factors that influence immiscible-liquid dissolution are incorporated into the calibrated dissolution rate coefficient, which in such cases serves as a composite or lumped term. The calibrated dissolution rate coefficients obtained from the simulations conducted with the lumped-process model were approximately two to three orders-of-magnitude smaller than the independently-determined values used for the simulations conducted with the distributed-process model. This disparity reflects the difference in implicit versus explicit consideration of the larger-scale factors influencing immiscible-liquid dissolution in the systems. © 2008 Elsevier B.V. All rights reserved.
• McColl, C. M., Johnson, G. R., & Brusseau, M. L. (2008). Evaporative mass transfer behavior of a complex immiscible liquid. Chemosphere, 73(4), 607-613.
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  PMID: 18614196;PMCID: PMC2886807;Abstract: A series of laboratory experiments was conducted with a multiple-component immiscible liquid, collected from the Picillo Farm Superfund Site in Rhode Island, to examine liquid-vapor mass-transfer behavior. The immiscible liquid, which comprises solvents, oils, pesticides, PCBs, paint sludges, explosives, and other compounds, was characterized using gas chromatography and gas chromatography/mass spectrometry to determine mole fractions of selected constituents. Batch experiments were conducted to evaluate equilibrium phase-partitioning behavior. Two sets of air-stripping column studies were conducted to examine the mass-transfer dynamics of five selected target compounds present in the immiscible-liquid mixture. One set of column experiments was designed to represent a system with free-phase immiscible liquid present; the other was designed to represent a system with a residual phase of immiscible liquid. Initial elution behavior of all target components generally appeared to be ideal for both systems, as the initial vapor-phase concentrations were similar to vapor-phase concentrations measured for the batch experiment and those estimated using Raoult's law (incorporating the immiscible-liquid composition data). Later-stage removal of 1,2-dichlorobenzene appeared to be rate limited for the columns containing free-phase immiscible liquid and no porous medium. Conversely, evaporative mass transfer appeared to be ideal throughout the experiment conducted with immiscible liquid distributed relatively uniformly as a residual phase within a sandy porous medium. © 2008 Elsevier Ltd. All rights reserved.
• Brusseau, M. L., Nelson, N. T., Zhang, Z., Blue, J. E., Rohrer, J., & Allen, T. (2007). Source-zone characterization of a chlorinated-solvent contaminated Superfund site in Tucson, AZ. Journal of Contaminant Hydrology, 90(1-2), 21-40.
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  PMID: 17049404;Abstract: An extensive site-characterization project was conducted at a large chlorinated-solvent contaminated Superfund site in Tucson, AZ. The project consisted of several components, including traditional site-characterization activities, tracer tests, laboratory experiments conducted with core material collected from the site, and mathematical modeling. The primary focus of the work presented herein is the analysis of induced-gradient contaminant elution tests conducted in a source zone at the site, investigation of the potential occurrence of immiscible liquid in the saturated zone, characterization of the relationship between mass flux reduction and mass removal, and evaluation of the impact of source-zone management on site remediation. The results of the present study, along with those of prior work, indicate that immiscible liquid is likely present in the saturated zone at the site source zones. Extensive tailing and rebound was observed for the contaminant-elution tests, indicating nonideal transport and mass-transfer behavior. The elution data were analyzed with a source-zone-scale mathematical model, and the results indicated that nonideal immiscible-liquid dissolution was the primary cause of the observed behavior. The time-continuous relationship between mass flux reduction and mass removal associated with the plume-scale pump-and-treat operation exhibited an initial large drop in mass flux with minimal mass removed, followed by a period of minimal mass flux reduction and a second period of large reduction. This behavior reflects the impact of both source-zone and aqueous-plume mass removal dynamics. Ultimately, a greater than 90% reduction in mass flux was achieved for a mass removal of approximately 50%. The influence of source-zone management on site remediation was evaluated by conducting two predictive simulations, one for which the source zones were controlled and one for which they were not. A plume-scale model was used to simulate the composite contaminant concentrations associated with groundwater extracted with the pump-and-treat system, which were compared to measured data. The information generated from this study was used to enhance the site conceptual model, help optimize operation of the pump-and-treat system, and evaluate the utility of source-zone remediation. © 2006 Elsevier B.V. All rights reserved.
• Brusseau, M. L., Peng, S., Schnaar, G., & Murao, A. (2007). Measuring air-water interfacial areas with X-ray microtomography and interfacial partitioning tracer tests. Environmental Science and Technology, 41(6), 1956-1961.
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  PMID: 17410790;Abstract: Air-water interfacial areas as a function of water saturation were measured for a sandy, natural porous medium using two methods, aqueous-phase interfacial partitioning tracer tests and synchrotron X-ray microtomography. In addition, interfacial areas measured in a prior study with the gas-phase interfacial partitioning tracer-test method for the same porous medium were included for comparison. For all three methods, total air-water interfacial areas increased with decreasing watersaturation. The interfacial areas measured with the tracer-test methods were generally larger than those obtained from microtomography, and the disparity increased as water saturation decreased. The interfacial areas measured by microtomography extrapolated to a value (147 cm-1) very similar to the specific solid surface area (151 cm -1) calculated using the smooth-sphere assumption, indicating that the method does not characterize the area associated with microscopic surface heterogeneity (surface roughness, microporosity). This is consistent with the method resolution of approximately 12 μm. In contrast, the interfacial areas measured with the gas-phase tracer tests approached the N2/BET measured specific solid surface area (56 000 cm-1), indicating that this method does characterize the interfacial area associated with microscopic surface heterogeneity. The largest interfacial area measured with the aqueous-phase tracer tests was 224 cm-1, while the extrapolated maximum interfacial area was approximately 1100 cm-1. Both of these values are larger than the smooth-sphere specific solid surface area but much smaller than the N2/BET specific solid surface area, which suggests that the method measures a limited portion of the interfacial area associated with microscopic surface heterogeneity. All three methods provide measures of total (capillary + film) interfacial area, a primary difference being that the film-associated area is a smooth-surface equivalent for the microtomography method. An advantage of the microtomography method is the ability to determine explicitly both total and capillary-associated interfacial areas, which is problematic for the tracer-test methods. © 2007 American Chemical Society.
• Ochoa-Loza, F. J., Noordman, W. H., Jannsen, D. B., Brusseau, M. L., & Maier, R. M. (2007). Effect of clays, metal oxides, and organic matter on rhamnolipid biosurfactant sorption by soil. Chemosphere, 66(9), 1634-1642.
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  PMID: 16965801;Abstract: Rhamnolipids produced by Pseudomonas aeruginosa have been proposed as soil washing agents for enhanced removal of metal and organic contaminants from soil. A potential limitation for the application of rhamnolipids is sorption by soil matrix components. The objective of this study is to empirically determine the contribution of representative soil constituents (clays, metal oxides, and organic matter) to sorption of the rhamnolipid form most efficient at metal complexation (monorhamnolipid). Sorption studies show that monorhamnolipid (R1) sorption is concentration dependent. At low R1 concentrations that are relevant for enhancing organic contaminant biodegradation, R1 sorption followed the order: hematite (Fe2O3) > kaolinite > MnO2 ≈ illite ≈ Ca-montmorillonite > gibbsite (Al(OH)3) > humic acid-coated silica. At high R1 concentrations, relevant for use in complexation/removal of metals or organics, R1 sorption followed the order: illite >> humic acid-coated silica > Ca-montmorillonite > hematite > MnO2 > gibbsite ≈ kaolinite. These results allowed prediction of R1 sorption by a series of six soils. Finally, a comparison of R1 and R2 (dirhamnolipid) shows that the R1 form sorbs more strongly alone than when in a mixture of both the R1 and R2 forms. The information presented can be used to estimate, on an individual soil basis, the extent of rhamnolipid sorption. This is important for determining: (1) whether rhamnolipid addition is a feasible remediation option and (2) the amount of rhamnolipid required to efficiently remove the contaminant. © 2006 Elsevier Ltd. All rights reserved.
• Simon, M. A., & Brusseau, M. L. (2007). Analysis of a gas-phase partitioning tracer test conducted in an unsaturated fractured-clay formation. Journal of Contaminant Hydrology, 90(3-4), 146-158.
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  PMID: 17157956;Abstract: The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured-clay system that is the confining layer for the underlying regional aquifer. Three suites of three tracers were injected into wells located 14, 24, and 24 m from a single, central extraction well. The tracers comprised noble gases (traditionally thought to be nonsorbing), alkanes (primarily water partitioning), perfluorides (primarily NAPL partitioning), and halons (both NAPL and water partitioning). Observations of vacuum response were consistent with flow in a fractured system. The halon tracers exhibited the greatest amount of retardation, and helium and the perfluoride tracers the least. The alkane tracers were unexpectedly more retarded than the perfluoride tracers, indicating low NAPL saturations and high water saturations. An NAPL saturation of 0.01, water saturation of 0.215, and gas saturation of 0.775 was estimated based on analysis of the suite of tracers comprising helium, perfluoromethylcyclohexane and dibromodifluoromethane, which was considered to be the most robust set. The estimated saturations compare reasonably well to independently determined values.
• Tick, G. R., McColl, C. M., Yolcubal, I., & Brusseau, M. L. (2007). Gas-phase diffusive tracer test for the in-situ measurement of tortuosity in the vadose zone. Water, Air, and Soil Pollution, 184(1-4), 355-362.
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  Abstract: Robust measurements of porous-medium tortuosity are one of the many components needed for accurate characterization and prediction of fluid flow and contaminant transport in the subsurface. A gas-phase diffusive tracer-test method is evaluated for the in-situ measurement of tortuosity in the vadose zone. This technique presents an alternative to employing widely-used correlations to estimate tortuosity. A small-scale field study was conducted using a single well and a non-reactive gas-phase tracer (sulfur hexafluoride; SF6). Gas samples were collected from the injection point periodically after tracer injection into the soil matrix. An effective radius of influence of 50 cm was determined for the tests. An analytical solution was calibrated to the measured temporal concentration distribution, producing a fitted value for tortuosity. The value obtained from the tracer tests was compared to values estimated with several widely-used correlations. The value obtained from the tracer tests was generally larger than the values estimated with the correlations, which spanned a relatively wide range. The tracer-test method provides a means by which to determine in-situ measurements of tortuosity, allowing for better characterization of contaminant transport in the vadose zone. © 2007 Springer Science+Business Media B.V.
• Brusseau, M. L., Peng, S., Schnaar, G., & Costanza-Robinson, M. S. (2006). Relationships among air-water interfacial area, capillary pressure, and water saturation for a sandy porous medium. Water Resources Research, 42(3).
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  Abstract: The relationships among air-water interfacial area, capillary pressure, and water saturation were investigated for a sandy, natural porous medium. Air-water interfacial areas as a function of water saturation were measured using two methods, gas phase partitioning tracer tests and synchrotron X-ray microtomography. The tracer test method provides a measure of effective total (capillary and film) interfacial area, whereas microtomography can be used to determine both capillary-associated and total areas (the latter is the focus of this study). Air-water interfacial areas determined with both methods increased continuously with decreasing water saturation. The areas measured with the tracer test method were significantly larger than those obtained from microtomography. The maximum values measured with the tracer test method approached the N2/BET-measured specific solid surface area, whereas the maximum values measured by microtomography approached the smooth-sphere-calculated specific solid surface area. The interfacial area-saturation data were combined with capillary pressure-saturation data obtained from water drainage experiments to examine the relationship between total air-water interfacial area and capillary pressure. Air-water interfacial area was observed to increase monotonically with increasing capillary pressure and then to plateau at values that correspond to areas associated with residual water saturation. These results are consistent with previously reported theoretically and computationally based analyses of functional relationships between total nonwetting-wetting interfacial area and capillary pressure. Copyright 2006 by the American Geophysical Union.
• Brusseau, M. L., Sandrin, S. K., Li, L., Yolcubal, I., Jordan, F. L., & Maier, R. M. (2006). Biodegradation during contaminant transport in porous media: 8. The influence of microbial system variability on transport behavior and parameter determination. Water Resources Research, 42(4).
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  Abstract: The impact of microbial system variability on the biodegradation and transport behavior of a model solute, salicylate, was investigated with a series of miscible displacement experiments. Four systems of increasing complexity were employed: a sterilized, well-sorted sand inoculated with a single bacterial isolate, a sterilized soil inoculated with the same isolate, and two soils, each of which contained an indigenous multiple-population community of bacteria. The experiments were conducted in replicate (three or four experiments per set) and with paired controls. The biodegradation and transport behavior of salicylate exhibited a small degree of variability among the replicates for the two inoculated systems and a relatively large degree of variability for the two indigenous systems. The greater variability observed for the two indigenous systems is attributed primarily to greater variability of microbial system properties, such as initial cell density, metabolic status, and community composition. Values for maximum specific growth rate coefficient, mean lag time, and lag time variance were determined by model calibration to the measured breakthrough curves and compared to values obtained from batch experiments. Reasonable correspondence was observed between the two sets of values for both the inoculated and indigenous systems. The maximum specific growth rate coefficient exhibited a relatively small degree of uncertainty for all four systems, whereas greater uncertainty was associated with the lag time mean and variance. The variability in calibrated parameters among each set of replicate experiments was significantly greater than the uncertainty associated with the individual experiment calibrations and the measured input parameters. These results illustrate that variability inherent to natural microbial systems can cause variability in transport behavior even under controlled laboratory conditions and concomitantly enhance the uncertainty of biokinetic parameters obtained from laboratory studies. Copyright 2006 by the American Geophysical Union.
• Brusseau, M., Carroll, K. C., Artiola, J. F., & Brusseau, M. L. (2006). Transport of molybdenum in a biosolid-amended alkaline soil. Chemosphere, 65(5).
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  The transport of molybdenum (Mo) in a biosolid-amended, alkaline, agricultural soil was examined in the research reported herein. Batch-equilibrium and miscible-displacement experiments were conducted to examine the transport of Mo in soil with and without 10% by weight biosolid amendment. The results of geochemical modeling, conducted using PHREEQC, indicated that no mineral dissolution or precipitation reactions were expected for the system under the prevailing conditions. Sorption equilibrium coefficients (Kd) obtained from moment analysis of the Mo breakthrough curves were similar to those calculated from the results of the batch-equilibrium experiments. Mo sorption was greater for the biosolid-amended soil (Kd of 1.3 versus 0.35). Sorption of Mo was shown to be linear, rate limited, and reversible for both unamended and amended soil. The results suggest that Mo associated with biosolid-amended soils is relatively bioavailable and mobile.
• Brusseau, M., Schnaar, G., & Brusseau, M. L. (2006). Characterizing pore-scale dissolution of organic immiscible liquid in natural porous media using synchrotron X-ray microtomography. Environmental science & technology, 40(21).
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  The objective of this study was to characterize the pore-scale dissolution of organic immiscible-liquid blobs residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of the aqueous, organic-liquid, and solid phases residing in columns packed with one of two porous media. Images of the packed columns were obtained after a stable, discontinuous distribution (e.g., residual saturation) of the organic liquid (trichloroethene) had been established, and three subsequent times during column flushing. These data were used to characterize the morphology of the organic-liquid blobs as a function of dissolution, and to quantify changes in total organic-liquid volume, surface area, and water-organic liquid interfacial area. The dissolution dynamics of individual blobs appeared to be influenced by the local pore configuration. In addition to dissolution-induced shrinkage, some blobs were observed to separate into multiple distinct subunits. The median blob size decreased by approximately a factor of 2 at the point where approximately 90% of the initial organic-liquid volume had been removed. The ratio of capillary associated interfacial area to total water-organic liquid interfacial area increased by 50% at the point where approximately 95% of the initial mass had been removed. A nearly linear relationship was observed between both total and capillary associated interfacial area and organic liquid volumetric fraction. Changes in the measured aqueous-phase trichloroethene effluent concentrations were well correlated with changes in the volume, surface area, and number of blobs. The effluent concentration data were adequately described by a first-order mass transfer expression employing a constant value of the mass-transfer coefficient, with values for the water-organic liquid interfacial area obtained independently from the microtomography data.
• Carroll, K. C., Artiola, J. F., & Brusseau, M. L. (2006). Transport of molybdenum in a biosolid-amended alkaline soil. Chemosphere, 65(5), 778-785.
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  PMID: 16674987;Abstract: The transport of molybdenum (Mo) in a biosolid-amended, alkaline, agricultural soil was examined in the research reported herein. Batch-equilibrium and miscible-displacement experiments were conducted to examine the transport of Mo in soil with and without 10% by weight biosolid amendment. The results of geochemical modeling, conducted using PHREEQC, indicated that no mineral dissolution or precipitation reactions were expected for the system under the prevailing conditions. Sorption equilibrium coefficients (Kd) obtained from moment analysis of the Mo breakthrough curves were similar to those calculated from the results of the batch-equilibrium experiments. Mo sorption was greater for the biosolid-amended soil (Kd of 1.3 versus 0.35). Sorption of Mo was shown to be linear, rate limited, and reversible for both unamended and amended soil. The results suggest that Mo associated with biosolid-amended soils is relatively bioavailable and mobile. © 2006 Elsevier Ltd. All rights reserved.
• Schnaar, G., & Brusseau, M. L. (2006). Characterizing pore-scale configuration of organic immiscible liquid in multiphase systems with synchrotron X-Ray microtomography. Vadose Zone Journal, 5(2), 641-648.
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  Abstract: The objective of this study was to examine the pore-scale distribution and morphology of organic immiscible liquid in natural porous media containing three immiscible fluids. High-resolution, three-dimensional images of an organic liquid (tetrachloroethene) in both three-phase (water-air-organic liquid) and two-phase (water-organic liquid) systems were obtained using synchrotron X-ray microtomography. These data were used to quantitatively characterize the morphology of the organic liquid residing within columns packed with one of three natural, sandy porous media. Organic-liquid blobs varied greatly in both size and shape, ranging from small, single spheres (≥0.03mmin diameter) to large, amorphous ganglia with mean lengths of 4 to 5 mm. Singlets comprised the greatest number of blobs, whereas the large ganglia, while much fewer in number, comprised the majority of the organic-liquid surface area and volume. A significant portion of the organic liquid in the three-phase systems was observed to exist as lenses and films in contact with air. These features were not observed in the two-phase water-organic liquid systems. The median of the blob-frequency distributions was smaller and the variance larger for the three-phase systems. In addition, the global specific surface areas of the organic liquid were greater for the three-phase systems. These differences are attributed to the presence of the organic-liquid lenses and films for the three-phase systems. © Soil Science Society of America.
• Schnaar, G., & Brusseau, M. L. (2006). Characterizing pore-scale dissolution of organic immiscible liquid in natural porous media using synchrotron x-ray microtomography. Environmental Science and Technology, 40(21), 6622-6629.
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  PMID: 17144287;Abstract: The objective of this study was to characterize the pore-scale dissolution of organic immiscible-liquid blobs residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of the aqueous, organic-liquid, and solid phases residing in columns packed with one of two porous media. Images of the packed columns were obtained after a stable, discontinuous distribution (e.g., residual saturation) of the organic liquid (trichloroethene) had been established, and three subsequent times during column flushing. These data were used to characterize the morphology of the organic-liquid blobs as a function of dissolution, and to quantify changes in total organic-liquid volume, surface area, and water-organic liquid interfacial area. The dissolution dynamics of individual blobs appeared to be influenced by the local pore configuration. In addition to dissolution-induced shrinkage, some blobs were observed to separate into multiple distinct subunits. The median blob size decreased by approximately a factor of 2 at the point where approximately 90% of the initial organic-liquid volume had been removed. The ratio of capillary associated interfacial area to total water-organic liquid interfacial area increased by 50% at the point where approximately 95% of the initial mass had been removed. A nearly linear relationship was observed between both total and capillary associated interfacial area and organic liquid volumetric fraction. Changes in the measured aqueous-phase trichloroethene effluent concentrations were well correlated with changes in the volume, surface area, and number of blobs. The effluent concentration data were adequately described by a first-order mass transfer expression employing a constant value of the mass-transfer coefficient, with values for the water-organic liquid interfacial area obtained independently from the microtomography data. © 2006 American Chemical Society.
• Simon, M. A., & Brusseau, M. L. (2006). Method for measuring air-immiscible liquid partition coefficients. Journal of Environmental Engineering, 132(1), 140-144.
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  Abstract: The principal objective of this work was to measure nonaqueous phase liquid-air partition coefficients for various gas tracer compounds. Known amounts of trichloroethene (TCE) and tracer, as neat compounds, were introduced into glass vials and allowed to equilibrate. The TCE and tracer concentration of the headspace was analyzed and the partition coefficient was calculated from a mass balance. The TCE-air partition coefficient, defined as the ratio of the concentration of the tracer in the vapor phase to its concentration in the TCE phase, for gas tracer compounds perfluorodimethylcyclobutane, perfluoromethylcyclopentane, perfluoromethylcyclohexane, dibromodifluoromethane, and dibromotetrafluoroethane were determined to be 22, 24, 53, 370, and 470 for temperatures of 22-28°C. Most of the variability follows from uncertainty with measurements of tracer vapor-phase concentrations, with overall relative percent differences ranging from 8.5 to 25%. This methodology produces results consistent with literature values obtained from column tests, with similar reproducibility. © 2006 ASCE.
• Brusseau, M., Schnaar, G., & Brusseau, M. L. (2005). Pore-scale characterization of organic immiscible-liquid morphology in natural porous media using synchrotron X-ray microtomography. Environmental science & technology, 39(21).
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  The objective of this study was to quantitatively characterize the pore-scale morphology of organic immiscible liquid residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of solid and liquid phases in packed columns. The image data were processed to generate quantitative measurements of organic-liquid blob morphology. Three porous media, comprising a range of particle-size distributions, were used to evaluate the impact of porous-medium texture on blob morphology. The sizes and shapes of the organic-liquid blobs varied greatly, ranging from small spherical singlets (> or = 0.03 mm in diameter) to large, amorphous ganglia with mean lengths of 4-5 mm. The smaller blobs were composed primarily of singlets, which comprised approximately half of all blobs for all three media. Conversely, large, complex blobs comprising four or more bodies composed 11-24% of the total number of blobs. However, the majority of the total organic-liquid surface area and volume was associated with the largest blobs. The ratio of median blob size to median grain size was close to unity for all three systems. The distribution of blob sizes was greatest for the porous medium with the broadest particle-size and pore-size distributions. These results illustrate the utility of synchrotron X-ray microtomography for characterizing fluid distributions at the pore scale in natural porous media.
• Brusseau, M., Wang, J., Maier, R. M., & Brusseau, M. L. (2005). Influence of hydroxypropyl-beta-cyclodextrin (HPCD) on the bioavailability and biodegradation of pyrene. Chemosphere, 60(5).
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  It is well known that the limited aqueous solubilities of polycyclic aromatic hydrocarbons (PAH) often reduce their bioavailability to bacterial populations. The objective of this study was to test the impact of a solubility-enhancement reagent, hydroxypropyl-beta-cyclodextrin (HPCD), on the bioavailability and biodegradation of pyrene. No measurable loss of pyrene occurred for the control vials throughout the first 22 weeks of the experiment, indicating the absence of mass loss via abiotic transformation and volatilization. The vials containing pyrene and the degrader isolate (Burkholderia CRE 7), but no HPCD, also exhibited no measurable loss of pyrene throughout the experiment. Conversely, biodegradation of pyrene appears to have been initiated after approximately 15 weeks for the vials containing 10(4) mg l(-1) HPCD. By the end of the experiment, approximately 14% (w/w) of the pyrene was biodegraded in the presence of HPCD. These results indicate that HPCD may be useful for enhancing the bioavailability and biodegradation of pyrene and other PAHs.
• Brusseau, M., Wang, J., Patterson, B., Bodour, A., Maier, R. M., & Brusseau, M. L. (2005). Biodegradation during contaminant transport in porous media: 7. Impact of multiple-degrader community dynamics. Environmental toxicology and chemistry / SETAC, 24(11).
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  The biodegradation and transport of phenanthrene in porous media containing multiple populations of phenanthrene degraders is examined with a series of miscible-displacement experiments. A long-term experiment was conducted with a soil containing an indigenous microbial community comprised of 25 identified phenanthrene-degrading isolates. The rate and magnitude of phenanthrene biodegradation oscillated throughout the six-month experiment. This behavior, at least in part, is attributed to multiple-population dynamics associated with the indigenous community of phenanthrene degraders, the composition of which changed during the experiment. This hypothesis is supported by the results of experiments conducted using sterilized porous media that were inoculated with selected isolates obtained from the indigenous soil community. The results of experiments conducted with sterilized soil inoculated with isolate A exhibited an initial extended period of steady phenanthrene effluent concentrations, followed by a uniform decline. The results of experiments conducted using sterilized sand for single-isolate systems with one of three selected isolates and for systems of two-isolate combinations, indicate the existence of apparent synergistic and antagonistic interactions among the isolates. For example, phenanthrene biodegradation was relatively extensive and occurred without a lag phase for isolate A alone. However, biodegradation was constrained when isolate A and B were combined, indicating an antagonistic interaction. Conversely, whereas extensive lag phases were exhibited by both isolates B and C for the single-isolate experiments, there was minimal lag when isolates B and C were combined, indicating a synergistic interaction.
• Dorn, J. G., Brusseau, M. L., & Maier, R. M. (2005). Real-time, in situ monitoring of bioactive zone dynamics in heterogeneous systems. Environmental Science and Technology, 39(22), 8898-8905.
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  PMID: 16329198;Abstract: Successful implementation of in situ bioremediation is contingent upon understanding how physicochemical and microbial factors affect the formation and dynamics of microbially active regions known as bioactive zones (BAZs). This study demonstrates how a novel fiber optic detection system can be used to test hypotheses concerning real-time, in situ BAZ formation and dynamics. This study focuses on naphthalene transport in saturated porous media containing defined physicochemical and microbial heterogeneities. Biological activity was measured using a lux reporter bacterium, Pseudomonas putida RB1353, that bioluminesces during naphthalene catabolism. Results show that the presence of defined heterogeneities drives the development of BAZs at material-property interfaces where the confluence of naphthalene, dissolved oxygen, and sufficient microbial density is optimal. Thus, despite successful transport of P. putida RB1353 into a sterile low-permeability region containing substrate, BAZ formation in this region was limited by local physicochemical conditions (e.g., naphthalene and dissolved oxygen bioavailability). In another instance, transport of P. putida RB1353 occurred against advective flow, resulting in BAZ formation upgradient of inoculated regions. Defined systems such as this can be used as a basis for predicting localization of activity in complex subsurface systems. © 2005 American Chemical Society.
• Peng, S., & Brusseau, M. L. (2005). Gas-phase partitioning tracer test method for water content measurement: Evaluating efficacy for a range of porous-medium textures. Vadose Zone Journal, 4(3), 881-884.
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  Abstract: Gas-phase partitioning tracer tests were conducted to measure water content for several porous media with different mean particle diameters and particle-size distributions. Methane was used as the nonreactive tracer and difluoromethane was used as the water-partitioning tracer. Water contents determined from the tracer-test results were similar to values measured gravimetrically. These results support the utility of the gas-phase tracer method for measuring water content in a variety of porous media. © Soil Science Society of America.
• Peng, S., & Brusseau, M. L. (2005). Impact of soil texture on air-water interfacial areas in unsaturated sandy porous media. Water Resources Research, 41(3), 1-8.
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  Abstract: The gas phase partitioning tracer method was used to measure air-water interfacial area as a function of water content for eight sandy porous media. The porous media comprised a series of sands with narrow particle size ranges, a sand with a wider particle size distribution, a sandy soil, and a loamy sandy soil. The measurement range was extended to very low water contents in an attempt to determine upper limits for air-water interfacial areas. The measured values were compared to the normalized surface areas of the porous media. The results of the experiments showed that the magnitude of the air-water interfacial areas increased with decreasing water saturation and approached that of the normalized surface areas. Generally, air-water interfacial areas were larger for media with larger specific surface areas. The change in air-water interfacial area with changing water saturation was less near saturated water contents and greater at smaller values. In addition, the change was greater for the poorly sorted media than the well-sorted media. An empirical equation was developed to describe the observed relationship between air-water interfacial area and water saturation. The coefficients of the equation were found to correlate to the porous medium uniformity coefficient. With this equation and associated correlations, only bulk density, specific surface area, and uniformity coefficient are needed to estimate air-water interfacial area for a given water saturation. The equation was shown to provide a reasonable description of a literature data set. Copyright 2005 by the American Geophysical Union.
• Schnaar, G., & Brusseau, M. L. (2005). Pore-scale characterization of organic immiscible-liquid morphology in natural porous media using synchrotron x-ray microtomography. Environmental Science and Technology, 39(21), 8403-8410.
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  PMID: 16294880;Abstract: The objective of this study was to quantitatively characterize the pore-scale morphology of organic immiscible liquid residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of solid and liquid phases in packed columns. The image data were processed to generate quantitative measurements of organic-liquid blob morphology. Three porous media, comprising a range of particle-size distributions, were used to evaluate the impact of porous-medium texture on blob morphology. The sizes and shapes of the organic-liquid blobs varied greatly, ranging from small spherical singlets (≥0.03 mm in diameter) to large, amorphous ganglia with mean lengths of 4-5 mm. The smaller blobs were composed primarily of singlets, which comprised approximately half of all blobs for all three media. Conversely, large, complex blobs comprising four or more bodies composed 11-24% of the total number of blobs. However, the majority of the total organic-liquid surface area and volume was associated with the largest blobs. The ratio of median blob size to median grain size was close to unity for all three systems. The distribution of blob sizes was greatest for the porous medium with the broadest particle-size and pore-size distributions. These results illustrate the utility of synchrotron X-ray microtomography for characterizing fluid distributions at the pore scale in natural porous media. © 2005 American Chemical Society.
• Wang, J., Maier, R. M., & Brusseau, M. L. (2005). Influence of hydroxypropyl-β-cyclodextrin (HPCD) on the bioavailability and biodegradation of pyrene. Chemosphere, 60(5), 725-728.
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  PMID: 15963811;Abstract: It is well known that the limited aqueous solubilities of polycyclic aromatic hydrocarbons (PAH) often reduce their bioavailability to bacterial populations. The objective of this study was to test the impact of a solubility-enhancement reagent, hydroxypropyl-β-cyclodextrin (HPCD), on the bioavailability and biodegradation of pyrene. No measurable loss of pyrene occurred for the control vials throughout the first 22 weeks of the experiment, indicating the absence of mass loss via abiotic transformation and volatilization. The vials containing pyrene and the degrader isolate (Burkholderia CRE 7), but no HPCD, also exhibited no measurable loss of pyrene throughout the experiment. Conversely, biodegradation of pyrene appears to have been initiated after approximately 15 weeks for the vials containing 10 4 mg l-1 HPCD. By the end of the experiment, approximately 14% (w/w) of the pyrene was biodegraded in the presence of HPCD. These results indicate that HPCD may be useful for enhancing the bioavailability and biodegradation of pyrene and other PAHs. © 2005 Elsevier Ltd. All rights reserved.
• Wang, J., Patterson, B., Bodour, A., Maier, R. M., & Brusseau, M. L. (2005). Biodegradation during contaminant transport in porous media: 7. Impact of multiple-degrader community dynamics. Environmental Toxicology and Chemistry, 24(11), 2806-2811.
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  PMID: 16398116;Abstract: The biodegradation and transport of phenanthrene in porous media containing multiple populations of phenanthrene degraders is examined with a series of miscible-displacement experiments. A long-term experiment was conducted with a soil containing an indigenous microbial community comprised of 25 identified phenanthrene-degrading isolates. The rate and magnitude of phenanthrene biodegradation oscillated throughout the six-month experiment. This behavior, at least in part, is attributed to multiple-population dynamics associated with the indigenous community of phenanthrene degraders, the composition of which changed during the experiment. This hypothesis is supported by the results of experiments conducted using sterilized porous media that were inoculated with selected isolates obtained from the indigenous soil community. The results of experiments conducted with sterilized soil inoculated with isolate A exhibited an initial extended period of steady phenanthrene effluent concentrations, followed by a uniform decline. The results of experiments conducted using sterilized sand for single-isolate systems with one of three selected isolates and for systems of two-isolate combinations, indicate the existence of apparent synergistic and antagonistic interactions among the isolates. For example, phenanthrene biodegradation was relatively extensive and occurred without a lag phase for isolate A alone. However, biodegradation was constrained when isolate A and B were combined, indicating an antagonistic interaction. Conversely, whereas extensive lag phases were exhibited by both isolates B and C for the single-isolate experiments, there was minimal lag when isolates B and C were combined, indicating a synergistic interaction. © 2005 SETAC.
• Brusseau, M., Wang, X., Yolcubal, I., Wang, W., Artiola, J., Maier, R., & Brusseau, M. L. (2004). Use of cyclodextrin and calcium chloride for enhanced removal of mercury from soil. Environmental toxicology and chemistry / SETAC, 23(8).
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  The use of solutions containing carboxymethyl-beta-cyclodextrin (CMCD) or CaCl2 for enhancing the removal of Hg from a sandy soil was investigated using batch and column experiments. The retention of Hg appeared to be controlled by specific adsorption reactions, which greatly constrained Hg removal when using water (KNO3 solution) to flush columns packed with contaminated soil. The results showed that the two reagents did enhance the removal of Hg from the soil. For example, 81% and 60% of Hg was recovered after 50 pore volumes of flushing with 50 mM CaCl2 and 2 mM CMCD, respectively, compared to 24% recovery for a 10 mM KNO3 solution. However, significant tailing and delayed recovery of Hg during the elution process occurred in the presence of all reagents, indicating that the removal of Hg from the soil was rate limited.
• Brusseau, M., Zhang, Z., & Brusseau, M. L. (2004). Nonideal transport of reactive contaminants in heterogeneous porous media: 7. distributed-domain model incorporating immiscible-liquid dissolution and rate-limited sorption/desorption. Journal of contaminant hydrology, 74(1-4).
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  The purpose of this work is to present a distributed-domain mathematical model incorporating the primary mass-transfer processes that mediate the transport of immiscible organic liquid constituents in water-saturated, locally heterogeneous porous media. Specifically, the impact of grain/pore-scale heterogeneity on immiscible-liquid dissolution and sorption/desorption is represented in the model by describing the system as comprising a continuous distribution of mass-transfer domains. With this conceptualization, the distributions of the initial dissolution rate coefficient and the sorption/desorption rate coefficient are represented as probability density functions. Several sets of numerical experiments are conducted to examine the effects of heterogeneous dissolution and sorption/desorption on contaminant transport and elution. Four scenarios with different combinations of uniform/heterogeneous rate-limited dissolution and uniform/heterogeneous rate-limited sorption/desorption are evaluated. The results show that both heterogeneous rate-limited sorption/desorption and heterogeneous rate-limited dissolution can significantly increase the time or pore volumes required to elute immiscible-liquid constituents from a contaminated porous medium. However, sorption/desorption has minimal influence on elution behavior until essentially all of the immiscible liquid has been removed. For typical immiscible-liquid constituents that have relatively low sorption, the asymptotic elution tailing produced by heterogeneous rate-limited sorption/desorption begins at effluent concentrations that are several orders of magnitude below the initial steady-state concentrations associated with dissolution of the immiscible liquid. Conversely, the enhanced elution tailing associated with heterogeneous rate-limited dissolution begins at concentrations that are approximately one-tenth of the initial steady-state concentrations. Hence, dissolution may generally control elution behavior of immiscible-liquid constituents in cases wherein grain/pore-scale heterogeneity significantly influences both dissolution and sorption/desorption.
• Dorn, J. G., Mahal, M. K., Brusseau, M. L., & Maier, R. M. (2004). Employing a novel fiber optic detection system to monitor the dynamics of in situ lux bioreporter activity in porous media: System performance update. Analytica Chimica Acta, 525(1), 63-74.
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  Abstract: One of the major constraints to successful implementation of in situ bioremediation is our lack of understanding of how microbial activity is influenced by the physicochemical conditions in the subsurface environment. Our laboratory has successfully developed a novel fiber optic detection system that employs a lux bioreporter organism to non-invasively monitor real-time, in situ microbial activity in porous media. An evaluation of potential system limitations indicates that the system is not adversely affected by biofilm formation on the optical fiber tips or by bioluminescence attenuation in the porous medium employed. Additionally, the detection system effectively captures the dynamics of in situ bacterial gene expression during naphthalene catabolism under changing physicochemical conditions in saturated porous media. Therefore, this system enables laboratory-based studies of how physicochemical conditions in the subsurface influence microbial activity and will assist in improving: (1) our fundamental understanding of how transformation-related non-ideality, such as non-steady-state microbial activity, affects contaminant transport and fate; and (2) our ability to predict the efficacy of in situ bioremediation in dynamic, heterogeneous subsurface environments. © 2004 Elsevier B.V. All rights reserved.
• Jordan, F. L., Sandrin, S. K., Frye, R. J., Brusseau, M. L., & Maier, R. M. (2004). The influence of system complexity on bacterial transport in saturated porous media. Journal of Contaminant Hydrology, 74(1-4), 19-38.
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  PMID: 15358485;Abstract: A series of miscible-displacement column experiments were conducted under saturated flow conditions to systematically investigate the influence of physical and biological complexity on bacterial activity and fate in the presence and absence of a non-sorbing growth substrate, salicylate. Bacterial elution was monitored for three different systems; System I - a sterilized, inoculated, well-sorted sand, System II - a sterilized, inoculated, heterogeneous loamy sand (Hayhook), and System III - two different unsterilized loamy sands (Hayhook and Vinton) each with their associated indigenous microbial community. Results show that System I behaved ideally with respect to both cell and substrate transport, wherein: (1) growth occurred in response to substrate addition, (2) cell elution increased in response to the substrate pulse, and (3) breakthrough curves were reproducible for both substrate and cell elution. In contrast, System II showed ideal behavior with respect to substrate transport but showed variable behavior for cell transport. Further, there was no measurable growth in response to substrate addition and no increase in cell elution during the salicylate pulse. System III exhibited non-ideal behavior for both substrate and cell transport. Of particular interest is the fact that the indigenous communities of the two soils behaved differently. Specifically, for the Hayhook soil, an increased elution response was observed for the heterotrophic population while the salicylate-degrading community was preferentially retained in the column. In contrast for the Vinton soil, the substrate pulse did not elicit an elution response from either the heterotrophic or salicylate-degrading community from the culturable, indigenous Vinton microorganisms. For Systems II and III, the observed variability appears to be associated with the biological component of the system, since sterile controls were reproducible. This type of systematic study is critical for understanding cell and substrate transport behavior in complex, heterogeneous systems, and illustrates the potential uncertainty associated with measurements in such systems. © 2004 Elsevier B.V. All rights reserved.
• Sandrin, S. K., Brusseau, M. L., Piatt, J. J., Bodour, A. A., Blanford, W. J., & Nelson, N. T. (2004). Spatial variability of in situ microbial activity: Biotracer tests. Ground Water, 42(3), 374-383.
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  PMID: 15161154;Abstract: Biotracer tests have been proposed as a means by which to characterize the in situ biodegradation potential for field-scale systems. In this study, field experiments were conducted at two sites to evaluate the utility of the biotracer method for characterizing the spatial variability of microbial activity. The first site is a mixed waste-contaminated surficial aquifer in Utah, and the second site is a chlorinated solvent-contaminated regional aquifer in Tucson, Arizona. Mass recovery of the biotracer decreased approximately linearly with increasing residence time for the Tucson site. Similar behavior was observed at the Utah site, except in the region adjacent to the injection zone, where percent recoveries were much lower than those predicted using a correlation determined using data collected downgradient of the injection zone. First-order biodegradation rate coefficients obtained from model calibration of the tracer data varied between 0.2 and 0.5/day for the Tucson site. For the Utah site, the values varied between 0.1 and 0.6/day downgradient of the injection wells, and between 0.7 and 2.6/day near the injection wells. Considering the large range over which biodegradation rate coefficients can vary, the rate coefficient exhibited relatively minimal spatial variability (factor of 2.5) for the Tucson site. Conversely, the spatial variability of the rate coefficient was an order of magnitude greater for the Utah site. These differences in variability are consistent with conditions associated with the respective sites. For example, the greater microbial activity observed in the vicinity of the injection wells for the Utah site is consistent with the biomass distribution determined from analysis of core samples, which shows larger bacterial cell densities for the region near the injection wells. These results illustrate the utility of biotracer tests for in situ characterization of microbial activity (e.g., biodegradation potential), including evaluation of potential spatial variability.
• Srivastava, R., Sharma, P. K., & Brusseau, M. L. (2004). Reactive solute transport in macroscopically homogeneous porous media: Analytical solutions for the temporal moments. Journal of Contaminant Hydrology, 69(1-2), 27-43.
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  PMID: 14972436;Abstract: In this work, we investigate one-dimensional solute transport affected by rate-limited sorption, first-order mass transfer, and first-order transformation. Analytical expressions are obtained for the temporal moments of the solute in the solution phase. The effect of various rate coefficients on the temporal moments is examined. It was found that, in the presence of transformation reactions, the mean arrival time, and the spread and skewness of the breakthrough curves, are not monotonic functions of the rate coefficients. These solutions will be useful as a preliminary analysis tool for ascertaining the relative importance of various processes under given conditions. They may also be used to analyze the accuracy of various numerical techniques used for simulation of reactive transport. © 2003 Elsevier B.V. All rights reserved.
• Wang, X., Yolcubal, I., Wang, W., Artiola, J., Maier, R., & Brusseau, M. (2004). Use of cyclodextrin and calcium chloride for enhanced removal of mercury from soil. Environmental Toxicology and Chemistry, 23(8), 1888-1892.
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  PMID: 15352477;Abstract: The use of solutions containing carboxymethyl-β-cyclodextrin (CMCD) or CaCl2 for enhancing the removal of Hg from a sandy soil was investigated using batch and column experiments. The retention of Hg appeared to be controlled by specific adsorption reactions, which greatly constrained Hg removal when using water (KNO3 solution) to flush columns packed with contaminated soil. The results showed that the two reagents did enhance the removal of Hg from the soil. For example, 81% and 60% of Hg was recovered after 50 pore volumes of flushing with 50 mM CaCl2 and 2 mM CMCD, respectively, compared to 24% recovery for a 10 mM KNO3 solution. However, significant tailing and delayed recovery of Hg during the elution process occurred in the presence of all reagents, indicating that the removal of Hg from the soil was rate limited.
• Zhang, Z., & Brusseau, M. L. (2004). Nonideal transport of reactive contaminants in heterogeneous porous media: 7. Distributed-domain model incorporating immiscible-liquid dissolution and rate-limited sorption/desorption. Journal of Contaminant Hydrology, 74(1-4), 83-103.
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  PMID: 15358488;Abstract: The purpose of this work is to present a distributed-domain mathematical model incorporating the primary mass-transfer processes that mediate the transport of immiscible organic liquid constituents in water-saturated, locally heterogeneous porous media. Specifically, the impact of grain/pore-scale heterogeneity on immiscible-liquid dissolution and sorption/desorption is represented in the model by describing the system as comprising a continuous distribution of mass-transfer domains. With this conceptualization, the distributions of the initial dissolution rate coefficient and the sorption/desorption rate coefficient are represented as probability density functions. Several sets of numerical experiments are conducted to examine the effects of heterogeneous dissolution and sorption/desorption on contaminant transport and elution. Four scenarios with different combinations of uniform/heterogeneous rate-limited dissolution and uniform/heterogeneous rate-limited sorption/desorption are evaluated. The results show that both heterogeneous rate-limited sorption/desorption and heterogeneous rate-limited dissolution can significantly increase the time or pore volumes required to elute immiscible-liquid constituents from a contaminated porous medium. However, sorption/desorption has minimal influence on elution behavior until essentially all of the immiscible liquid has been removed. For typical immiscible-liquid constituents that have relatively low sorption, the asymptotic elution tailing produced by heterogeneous rate-limited sorption/desorption begins at effluent concentrations that are several orders of magnitude below the initial steady-state concentrations associated with dissolution of the immiscible liquid. Conversely, the enhanced elution tailing associated with heterogeneous rate-limited dissolution begins at concentrations that are approximately one-tenth of the initial steady-state concentrations. Hence, dissolution may generally control elution behavior of immiscible-liquid constituents in cases wherein grain/pore-scale heterogeneity significantly influences both dissolution and sorption/desorption. © 2004 Elsevier B.V. All rights reserved.
• Alter, S. R., Brusseau, M. L., Piatt, J. J., Ray-Maitra, A., Wang, J. -., & Cain, R. B. (2003). Use of tracer tests to evaluate the impact of enhanced-solubilization flushing on in-situ biodegradation. Journal of Contaminant Hydrology, 64(3-4), 191-202.
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  PMID: 12814880;Abstract: Tracer tests were conducted to evaluate the effect of a complexing sugar flush (CSF) on in-situ biodegradation potential at a site contaminated by jet fuel, solvents, and other organic compounds. Technical-grade hydroxypropyl-β-cyclodextrin was used during the CSF study, which was conducted in a hydraulically isolated cell emplaced in a surficial aquifer. In-situ biodegradation potential was assessed with the use of tracer tests, which were conducted prior to and immediately following the CSF study. Ethanol, hexanol, and benzoate were used as the biodegradable tracers, while bromide was used as a nonreactive tracer. The results indicate that the biodegradation of benzoate was similar for both tracer tests. Conversely, the biodegradation of ethanol (23% increase) and hexanol (41% increase) was greater for the post-CSF tracer test. In addition, analysis of core samples collected from within the test cell indicates that the population density of aerobic jet-fuel degraders increased in the vicinity of the injection wells during the CSF. These results indicate that the cyclodextrin flush did not deleteriously affect the indigenous microbial community. This study illustrates that tracer tests can be used to evaluate the impact of remediation activities on in-situ biodegradation potential. © 2003 Elsevier Science B.V. All rights reserved.
• Bodour, A. A., Wang, J., Brusseau, M. L., & Maier, R. M. (2003). Temporal change in culturable phenanthrene degraders in response to long-term exposure to phenanthrene in a soil column system. Environmental Microbiology, 5(10), 888-895.
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  PMID: 14510842;Abstract: Widespread environmental contamination by polycyclic aromatic hydrocarbons (PAH) has led to increased interest in the use of natural attenuation as a clean-up strategy. However, few bioremediation studies have investigated the behaviour of the indigenous PAH-degrading community after long-term exposure to a PAH. In this study, a column packed with sandy loam soil was exposed to a solution saturated with phenanthrene (≈ 1.2 mg 1-1) for a 6-month period to examine the temporal response of the indigenous phenanthrene-degrading community. Initial soil, effluent, and final soil samples were collected and analysed for phenanthrene concentration and culturable phenanthrene degraders. Phenanthrene-degrading isolates were grouped by colony morphology. For each unique group, 16S rDNA polymerase chain reaction was performed, and then sequencing analysis was used to identify the isolate at the genus level. Twenty-five phenanthrene-degrading isolates, potentially representing 19 genera, were obtained from this analysis. Of these, eight genera have not been reported previously to degrade phenanthrene, including Afipia, Janthinobacterium, Leptothrix, Massilia, Methylobacterium, Rhizobium, Sinorhizobium and Thiobacillus. Results indicate that the dominant phenanthrene-degrading population changed over the course of this 6-month experiment. Specifically, the isolates obtained initially from the soil were not subsequently found in either effluent samples or the soil at the end of the experiment. Furthermore, several isolates that were found in the soil at the end of the experiment were not observed in the soil initially or in the effluent samples. This study confirms earlier findings indicating that a diverse community participates in phenanthrene degradation in the environment, and also suggests that the composition of this community is temporally variable.
• Brusseau, M. L., Bronson, K. M., Ross, S., Nelson, N. T., & Carlson, T. D. (2003). Application of gas-phase partitioning tracer tests to characterize immiscible-liquid contamination in the vadose zone beneath a fuel depot. Vadose Zone Journal, 2(2), 148-153.
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  Abstract: Gas-phase partitioning tracer tests were conducted at a fuel depot to evaluate the utility of the partitioning tracer method for characterizing organic immiscible-liquid contamination in the vadose zone. One test was conducted within the boundaries of an existing fuel dispensing island and former underground fuel tank facility. Core sampling indicated that the vadose zone at this location is heavily contaminated throughout its vertical extent by fuel-related hydrocarbons. A tracer test was conducted after 30 mo of operation of a soil vapor extraction (SVE) system. Analysis of hydrocarbon concentrations in the SVE effluent indicates that approximately 355 000 L of hydrocarbons were recovered during the 30-mo operation period. Comparing this value to the initial volume of hydrocarbons present, estimated to be approximately 454 000 L based on core data, produces an estimate of 99 000 (64 000-134 000) L of hydrocarbons remaining within the area influenced by the SVE system. Extrapolation of the tracer test results (S n = 0.44%) to the SVE-impacted zone produces an estimate of 107 000 (59 000-155 000) L of hydrocarbon present. The two values and associated approximate uncertainty ranges are relatively similar. The second test was conducted approximately 200 m from the former tank facility. Analysis of borehole material collected during well drilling at this location indicates minimal hydrocarbon contamination of the vadose zone, except in the vicinity of the water table (approximately 30 m below ground surface [bgs]), on which floating free product is found. Analysis of the tracer test results produced a hydrocarbon saturation value of 0.37%, which is significantly smaller than the initial value of approximately 1.9% (i.e., before SVE operation) estimated based on core data for the former tank facility location. The lower level of vadose-zone contamination suggests that the source of immiscible-liquid contamination found at the second location may be related to lateral migration of floating free product along the water table from the up-gradient tank facility, rather than vertical migration from the surface above. However, additional studies would be required to more fully evaluate this hypothesis. The results of this work illustrate the utility of the gas-phase partitioning tracer method for characterizing immiscible-liquid contamination in the vadose zone.
• Brusseau, M. L., Nelson, N. T., & Costanza-Robinson, M. S. (2003). Partitioning tracer tests for characterizing immiscible-fluid saturations and interfacial areas in the vadose zone. Vadose Zone Journal, 2(2), 138-147.
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  Abstract: Contaminant-transport analyses, risk assessments, and site remediations are all constrained by the complexity of the subsurface environment and by our insufficient knowledge of that environment. Most current subsurface characterization methods provide measurements for very small spatial domains, such that they are essentially point values. While such methods can provide accurate and precise data for small scales, their use for characterizing larger domains is generally constrained by sample-size limitations. Thus, methods that provide measurements at larger scales are being developed to complement the point-sampling methods. One such group of methods is based on the use of tracer tests. This review will cover "partitioning" tracer tests, which can be used to measure immiscible-liquid saturation of organic contaminants, soil water content, and fluid-fluid interfacial areas in subsurface systems. The conceptual basis and implementation of these methods will be briefly reviewed, with a focus on vadose zone applications.
• Brusseau, M., Famisan, G. B., & Brusseau, M. L. (2003). Biodegradation during contaminant transport in porous media: 6. Impact of sorption on coupled degradation-transport behavior. Environmental toxicology and chemistry / SETAC, 22(3).
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  Bioavailability is one of the critical factors influencing the biodegradation and bioremediation of organic compounds. The bioavailability of many organic contaminants is controlled in part by the nature, magnitude, and rate of sorption/desorption processes. This study investigates the impact of sorption and associated retardation on the bioavailability and biodegradation of aromatic hydrocarbons during transport in porous media. Miscible-displacement experiments were conducted using naphthalene and 2-naphthol as the model sorbing compounds and salicylate, a degradation product of naphthalene, as a nonsorbing reference compound. Two porous media were used, one (Eustis soil, FL, USA) with moderate sorption capacity and one (quartz sand) with no measurable sorption of the compounds. The porous media were sterilized and inoculated with Pseudomonas putida RB1353, an organism that degrades naphthalene and its derivatives. The biodegradation and transport of all three substrates in quartz sand were significantly influenced by microbial lag, the effects of which were observed within two to three pore volumes (3-4.5 h). This was also true for salicylate transport in the Eustis soil system. Conversely, biodegradation lag effects were not observed for naphthalene or 2-naphthol in the Eustis soil system. In addition, the masses of naphthalene and 2-naphthol degraded were significantly greater for the Eustis soil system compared to the quartz sand system. As noted previously, naphthalene and 2-naphthol were sorbed by the Eustis soil but not the quartz sand, while salicylate was not sorbed by either media. These results indicate that the increased residence time associated with sorption of naphthalene and 2-naphthol by Eustis soil enhanced overall biodegradation and obviated the impact of lag on observed transport behavior.
• Brusseau, M., Johnson, G. R., Gupta, K., Putz, D. K., Hu, Q., & Brusseau, M. L. (2003). The effect of local-scale physical heterogeneity and nonlinear, rate-limited sorption/desorption on contaminant transport in porous media. Journal of contaminant hydrology, 64(1-2).
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  Nonideal transport of contaminants in porous media has often been observed in laboratory characterization studies. It has long been recognized that multiple processes associated with both physical and chemical factors can contribute to this nonideal transport behavior. To fully understand system behavior, it is important to determine the relative contributions of these multiple factors when conducting contaminant transport and fate studies. In this study, the relative contribution of physical-heterogeneity-related processes versus those of nonlinear, rate-limited sorption/desorption to the observed nonideal transport of trichloroethene in an undisturbed aquifer core was determined through a series of miscible-displacement experiments. The results of experiments conducted using the undisturbed core, collected from a Superfund site in Tucson, AZ, were compared to those obtained from experiments conducted using the same aquifer material packed homogeneously. The results indicate that both physical and chemical factors, specifically preferential flow and associated rate-limited diffusive mass-transfer and rate-limited sorption/desorption, respectively, contributed to the nonideal behavior observed for trichloroethene transport in the undisturbed core. A successful prediction of trichloroethene transport in the undisturbed core was made employing a mathematical model incorporating multiple sources of nonideal transport, using independently determined model parameters to account for the multiple factors contributing to the nonideal transport behavior. The simulation results indicate that local-scale physical heterogeneity controlled the nonideal transport behavior of trichloroethene in the undisturbed core, and that nonlinear, rate-limited sorption/desorption were of secondary importance.
• Brusseau, M., Keller, J. M., & Brusseau, M. L. (2003). In-situ characterization of soil-water content using gas-phase partitioning tracer tests: field-scale evaluation. Environmental science & technology, 37(14).
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  Field-scale tests were performed to evaluate the effectiveness of the gas-phase partitioning tracer method for in-situ measurement of soil-water content. The tracer tests were conducted before and after a controlled infiltration event to evaluate performance at two water contents. Nonpartitioning (sulfur hexafluoride) and water-partitioning (difluoromethane) tracers were injected into the test zone, and their effluent breakthrough curves were analyzed using the method of moments to calculate retardation factors for difluoromethane. Soil-water contents estimated using the tracer data were compared to soil-water contents obtained independently using gravimetric core analysis, neutron scattering, and bore-hole ground penetrating radar. For the test conducted under drier soil conditions, the soil-water content estimated from the tracer test was identical to the independently measured values of 8.6% (equivalent to water saturation of 23%). For the test conducted under wetter soil conditions, the tracer test derived soil-water content was 81% of the independently measured values of 12.2% (equivalent to water saturation of 32%). The reduced efficacy at the higher soil-water content may reflectthe impact of advective and/ or diffusive mass transfer constraints on gas-phase transport. The results presented herein indicate that the partitioning tracer method is an effective technique to measure soil-water content at the field scale, especially for sites with moderate to low soil-water contents.
• Brusseau, M., Tick, G. R., Lourenso, F., Wood, A. L., & Brusseau, M. L. (2003). Pilot-scale demonstration of cyclodextrin as a solubility-enhancement agent for remediation of a tetrachloroethene-contaminated aquifer. Environmental science & technology, 37(24).
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  The limitations associated with conventional pump and treat technology have generated interest in using enhanced in-situ flushing as an alternative for remediating source zones contaminated with immiscible liquid. This research investigates the effectiveness of cyclodextrin as a solubility-enhancement agent to enhance the removal of tetrachloroethene (PCE) from a physically isolated section of an aquifer. An important component of this project was the implementation of reagent recovery and reuse. This field experiment presented the rare opportunity, under strict regulatory guidance, to inject PCE into the surficial aquifer cell created with two sets of sheet piles driven into an underlying clay unit. The well-controlled conditions specific to this experiment allowed quantification of mass balances, which is problematic for many contaminated field sites. The fact that mass balances can be obtained provides the ability to determine remediation effectiveness with unusual accuracy for a field project. The saturated zone within the test cell was flushed with a 15 wt % cyclodextrin solution. The cyclodextrin solution increased the aqueous concentration of PCE in the extraction-well effluent to as much as 22 times the concentrations obtained during the water flush conducted prior to the complexing sugar flush (CSF). The seven pore-volume CSF removed the equivalent of approximately 33 L of PCE from the subsurface. This equates to 48% of the total initial mass, based on the volume of PCE present prior to the CSF (68.6 L). Conversely, the seven pore-volume water flush conducted prior to the CSF removed the equivalent of 2.7 L of PCE. The use of cyclodextrin as a flushing agent, especially in a recycling configuration, appears to hold promise for successful remediation of chlorinated-solvent-contaminated source zones.
• Brusseau, M., Yolcubal, I., Dorn, J. G., Maier, R. M., & Brusseau, M. L. (2003). The influence of substrate and electron acceptor availability on bioactive zone dynamics in porous media. Journal of contaminant hydrology, 66(3-4).
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  Two approaches were used to investigate the influence of dissolved oxygen (DO) and substrate availability on the formation and dynamics of "bioactive zones" in a water-saturated porous medium. A bioactive zone is defined as a region where a microbial community is sufficiently active to metabolize bioavailable substrates. In the first approach, microbial activity was characterized by monitoring the spatial and temporal variability of DO and aqueous substrate (salicylate and naphthalene) concentrations during miscible-displacement experiments. In the second approach, microbial activity was monitored using multiple fiber optics emplaced in the porous medium to detect luminescence produced by Pseudomonas putida RB1353, a bioluminescent reporter organism that produces light when salicylate (an intermediate of naphthalene degradation) is present. The results of both approaches show that the location and size of the bioactive zones were influenced by in situ DO and substrate availability. When DO was not a limiting factor (i.e., lower substrate input concentrations), the bioactive zone encompassed the entire column, with the majority of the microbial activity occurring between the inlet and midpoint. However, as the availability of DO became limiting for the higher substrate input experiments, the size of the bioactive zone shrank and was ultimately limited to the proximity of the column inlet.
• Carlson, T. D., Costanza-Robinson, M., Keller, J., Wierenga, P. J., & Brusseau, M. L. (2003). Intermediate-scale tests of the gas-phase partitioning tracer method for measuring soil-water content. Soil Science Society of America Journal, 67(2), 483-486.
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  Abstract: Experiments were conducted in a well-instrumented weighing lysimeter (2.5 by 4 m) to evaluate the efficacy of the gas-phase-partitioning tracer method for measuring soil-water content. The method is based on the use of conservative (nonpartitioning) and water-partitioning tracers, wherein the partitioning tracer transfers into the water, which retards its movement with respect to that of the nonpartitioning tracer. This retardation is a function of the soil-water content. The volumetric soil-water contents estimated from comparative moment analysis of the measured breakthrough curves were compared with values obtained using traditional methods, including gravimetric core analysis, neutron thermalization, time domain reflectometry, and conversion of soil tension. The values obtained from the tracer tests compare favorably with the independently determined values. For the lower soil-water contents (6-7%), the tracer-estimated values were ≈98% of the measured values. For the higher soil-water content (15%), the tracer estimated values were ≈77% of the measured values. These results indicate that the gas-phase partitioning tracer method can provide representative estimates of soil-water content under the relatively ideal conditions employed herein.
• Costanza-Robinson, M., & Brusseau, M. L. (2003). Erratum: Air-water interfacial areas in unsaturated soils: Evaluation of interfacial domains (Water Resources Research (2003) 39:4 (1091) DOI: 10.1029/2003WR002018). Water Resources Research, 39(4), COR21.
• Famisan, G. B., & Brusseau, M. L. (2003). Biodegradation during contaminant transport in porous media: 6. Impact of sorption on coupled degradation-transport behavior. Environmental Toxicology and Chemistry, 22(3), 510-517.
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  PMID: 12627636;Abstract: Bioavailability is one of the critical factors influencing the biodegradation and bioremediation of organic compounds. The bioavailability of many organic contaminants is controlled in part by the nature, magnitude, and rate of sorption/desorption processes. This study investigates the impact of sorption and associated retardation on the bioavailability and biodegradation of aromatic hydrocarbons during transport in porous media. Miscible-displacement experiments were conducted using naphthalene and 2-naphthol as the model sorbing compounds and salicylate, a degradation product of naphthalene, as a nonsorbing reference compound. Two porous media were used, one (Eustis soil, FL, USA) with moderate sorption capacity and one (quartz sand) with no measurable sorption of the compounds. The porous media were sterilized and inoculated with Pseudomonas putida RB1353, an organism that degrades naphthalene and its derivatives. The biodegradation and transport of all three substrates in quartz sand were significantly influenced by microbial lag, the effects of which were observed within two to three pore volumes (3-4.5 h). This was also true for salicylate transport in the Eustis soil system. Conversely, biodegradation lag effects were not observed for naphthalene or 2-naphthol in the Eustis soil system. In addition, the masses of naphthalene and 2-naphthol degraded were significantly greater for the Eustis soil system compared to the quartz sand system. As noted previously, naphthalene and 2-naphthol were sorbed by the Eustis soil but not the quartz sand, while salicylate was not sorbed by either media. These results indicate that the increased residence time associated with sorption of naphthalene and 2-naphthol by Eustis soil enhanced overall biodegradation and obviated the impact of lag on observed transport behavior.
• Johnson, G. R., Gupta, K., Putz, D. K., Hu, Q., & Brusseau, M. L. (2003). The effect of local-scale physical heterogeneity and nonlinear, rate-limited sorption/desorption on contaminant transport in porous media. Journal of Contaminant Hydrology, 64(1-2), 35-58.
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  PMID: 12744828;Abstract: Nonideal transport of contaminants in porous media has often been observed in laboratory characterization studies. It has long been recognized that multiple processes associated with both physical and chemical factors can contribute to this nonideal transport behavior. To fully understand system behavior, it is important to determine the relative contributions of these multiple factors when conducting contaminant transport and fate studies. In this study, the relative contribution of physical-heterogeneity-related processes versus those of nonlinear, rate-limited sorption/desorption to the observed nonideal transport of trichloroethene in an undisturbed aquifer core was determined through a series of miscible-displacement experiments. The results of experiments conducted using the undisturbed core, collected from a Superfund site in Tucson, AZ, were compared to those obtained from experiments conducted using the same aquifer material packed homogeneously. The results indicate that both physical and chemical factors, specifically preferential flow and associated rate-limited diffusive mass-transfer and rate-limited sorption/desorption, respectively, contributed to the nonideal behavior observed for trichloroethene transport in the undisturbed core. A successful prediction of trichloroethene transport in the undisturbed core was made employing a mathematical model incorporating multiple sources of nonideal transport, using independently determined model parameters to account for the multiple factors contributing to the nonideal transport behavior. The simulation results indicate that local-scale physical heterogeneity controlled the nonideal transport behavior of trichloroethene in the undisturbed core, and that nonlinear, rate-limited sorption/desorption were of secondary importance. © 2003 Elsevier Science B.V. All rights reserved.
• Johnson, G. R., Zhang, Z., & Brusseau, M. L. (2003). Characterizing and quantifying the impact of immiscible-liquid dissolution and nonlinear, rate-limited sorption/desorption on low-concentration elution tailing. Water Resources Research, 39(5), SBH61-SBH68.
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  Abstract: Long-term elution tailing of organic contaminants, often observed when water or air is used to flush contaminated porous media, has been attributed to several factors. Characterization of this tailing behavior through the quantitative analysis of multiple coupled factors is necessary to enhance our understanding of contaminant transport. The objective of this study was to investigate the transport and elution behavior of trichloroethene in a naturally heterogeneous (poorly sorted) aquifer material, with a specific focus on characterizing and quantifying the relative contributions of rate-limited immiscible-liquid dissolution and nonlinear, rate-limited sorption/desorption to low-concentration elution tailing. A comparison of trichloroethene elution behavior for systems with and without immiscible-liquid phase present suggests that the low-concentration elution tailing observed in the former experiments is associated primarily with nonlinear, rate-limited sorption/desorption. The transport and elution of trichloroethene was successfully simulated using a mathematical model that combines independent, coupled descriptions of rate-limited dissolution and nonlinear, rate-limited sorption/desorption. Specifically, immiscible-liquid dissolution was described using a first-order mass transfer approach with a temporally variable dissolution rate coefficient, and sorption/desorption was described using an approach incorporating a continuous distribution of rate-limited domains. The results of this study indicate that multiple processes contributed to trichloroethene elution behavior when immiscible-liquid phase was present and that a multiprocess model was required to accurately simulate the measured data.
• Keller, J. M., & Brusseau, M. L. (2003). In-situ characterization of soil-water content using gas-phase partitioning tracer tests: Field-scale evaluation. Environmental Science and Technology, 37(14), 3141-3144.
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  PMID: 12901662;Abstract: Field-scale tests were performed to evaluate the effectiveness of the gas-phase partitioning tracer method for in-situ measurement of soil-water content. The tracer tests were conducted before and after a controlled infiltration event to evaluate performance at two water contents. Nonpartitioning (sulfur hexafluoride) and water-partitioning (difluoromethane) tracers were iniected into the test zone, and their effluent breakthrough curves were analyzed using the method of moments to calculate retardation factors for difluoromethane. Soil-water contents estimated using the tracer data were compared to soil-water contents obtained independently using gravimetric core analysis, neutron scattering, and bore-hole ground penetrating radar. For the test conducted under drier soil conditions, the soil-water content estimated from the tracer test was identical to the independently measured values of 8.6% (equivalent to water saturation of 23%). For the test conducted under wetter soil conditions, the tracer test derived soil-water content was 81% of the independently measured values of 12.2% (equivalent to water saturation of 32%). The reduced efficacy at the higher soil-water content may reflect the impact of advective and/or diffusive mass transfer constraints on gas-phase transport. The results presented herein indicate that the partitioning tracer method is an effective technique to measure soil-water content at the field scale, especially for sites with moderate to low soil-water contents.
• Nelson, N. T., Hu, Q., & Brusseau, M. L. (2003). Characterizing the contribution of diffusive mass transfer to solute transport in sedimentary aquifer systems at laboratory and field scales. Journal of Hydrology, 276(1-4), 275-286.
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  Abstract: The multi-tracer test method was used to investigate the impact of diffusion-mediated mass-transfer processes associated with physical heterogeneity on solute transport in sedimentary aquifer systems at different scales. Three systems were examined: (1) a column packed with homogenized aquifer material, (2) undisturbed aquifer cores, and (3) a section of a semi-confined alluvial aquifer encompassing approximately 2000 m2. Tracer experiments were conducted using non-reactive tracers with different aqueous diffusion coefficients, based on the assumption that the impact of diffusion-mediated mass-transfer processes on solute transport will be dependent upon the magnitude of the diffusion coefficient. For the homogenized packed column, the breakthrough curves for the different tracers were very similar, and the attendant dispersivities were identical. These results indicate, as would be expected, that physical-heterogeneity related diffusive mass transfer did not measurably contribute to solute transport in the homogeneously packed column. Conversely, the results obtained for the undisturbed aquifer cores indicate that diffusive mass transfer, possibly associated with diffusion between zones of lower and higher advection, contributed to solute transport in this system. For the field test, the magnitudes of the dispersivity coefficients were different for the different tracers. Thus, solute transport at the field scale appeared to be influenced by diffusive mass transfer, most likely associated with mass transfer between regions of lower and higher permeability. These results illustrate that tracer tests using tracers with different diffusivities can be used to help elucidate the relative contribution of diffusion-mediated mass transfer to solute transport. © 2003 Elsevier Science B.V. All rights reserved.
• Tick, G. R., Lourenso, F., Wood, A. L., & Brusseau, M. L. (2003). Pilot-Scale Demonstration of Cyclodextrin as a Solubility-Enhancement Agent for Remediation of a Tetrachloroethene-Contaminated Aquifer. Environmental Science and Technology, 37(24), 5829-5834.
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  PMID: 14717202;Abstract: The limitations associated with conventional pump and treat technology have generated interest in using enhanced in-situ flushing as an alternative for remediating source zones contaminated with immiscible liquid. This research investigates the effectiveness of cyclodextrin as a solubility-enhancement agent to enhance the removal of tetrachloroethene (PCE) from a physically isolated section of an aquifer. An important component of this project was the implementation of reagent recovery and reuse. This field experiment presented the rare opportunity, under strict regulatory guidance, to inject PCE into the surficial aquifer cell created with two sets of sheet piles driven into an underlying clay unit. The well-controlled conditions specific to this experiment allowed quantification of mass balances, which is problematic for many contaminated field sites. The fact that mass balances can be obtained provides the ability to determine remediation effectiveness with unusual accuracy for a field project. The saturated zone within the test cell was flushed with a 15 wt % cyclodextrin solution. The cyclodextrin solution increased the aqueous concentration of PCE in the extraction-well effluent to as much as 22 times the concentrations obtained during the water flush conducted prior to the complexing sugar flush (CSF). The seven pore-volume CSF removed the equivalent of approximately 33 L of PCE from the subsurface. This equates to 48% of the total initial mass, based on the volume of PCE present prior to the CSF (68.6 L). Conversely, the seven pore-volume water flush conducted prior to the CSF removed the equivalent of 2.7 L of PCE. The use of cyclodextrin as a flushing agent, especially in a recycling configuration, appears to hold promise for successful remediation of chlorinated-solvent-contaminated source zones.
• Yolcubal, I., Dorn, J. G., Maier, R. M., & Brusseau, M. L. (2003). The influence of substrate and electron acceptor availability on bioactive zone dynamics in porous media. Journal of Contaminant Hydrology, 66(3-4), 219-237.
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  PMID: 14568400;Abstract: Two approaches were used to investigate the influence of dissolved oxygen (DO) and substrate availability on the formation and dynamics of "bioactive zones" in a water-saturated porous medium. A bioactive zone is defined as a region where a microbial community is sufficiently active to metabolize bioavailable substrates. In the first approach, microbial activity was characterized by monitoring the spatial and temporal variability of DO and aqueous substrate (salicylate and naphthalene) concentrations during miscible-displacement experiments. In the second approach, microbial activity was monitored using multiple fiber optics emplaced in the porous medium to detect luminescence produced by Pseudomonas putida RB1353, a bioluminescent reporter organism that produces light when salicylate (an intermediate of naphthalene degradation) is present. The results of both approaches show that the location and size of the bioactive zones were influenced by in situ DO and substrate availability. When DO was not a limiting factor (i.e., lower substrate input concentrations), the bioactive zone encompassed the entire column, with the majority of the microbial activity occurring between the inlet and midpoint. However, as the availability of DO became limiting for the higher substrate input experiments, the size of the bioactive zone shrank and was ultimately limited to the proximity of the column inlet. © 2003 Elsevier Science B.V. All rights reserved.
• Brusseau, M. L., Zhang, Z., Nelson, N. T., Cain, R. B., Tick, G. R., & Oostrom, M. (2002). Dissolution of nonuniformly distributed immiscible liquid: Intermediate-scale experiments and mathematical modeling. Environmental Science and Technology, 36(5), 1033-1041.
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  PMID: 11917988;Abstract: The purpose of this work is to examine the effect of nonuniform distributions of immiscible organic liquid on dissolution behavior, with a specific focus on the condition dependency of dissolution (i.e., mass transfer) rate coefficients associated with applying mathematical models of differing complexities to measured data. Dissolution experiments were conducted using intermediate-scale flow cells packed with sand in which well-characterized zones of residual trichloroethene (TCE) and 1,2-dichloroethane (DCA) saturation were emplaced. A dual-energy gamma radiation system was used for in-situ measurement of NAPL saturation. Aqueous concentrations of TCE and DCA measured in the flow-cell effluent were significantly less than solubility, due primarily to dilution associated with the nonuniform immiscible-liquid distribution and bypass flow effects associated with physical heterogeneity. A quantitative analysis of flow and transport was conducted using a three-dimensional mathematical model wherein immiscible-liquid distribution, permeability variability, and sampling effects were explicitly considered. Independent values for the initial dissolution rate coefficients were obtained from dissolution experiments conducted using homogeneously packed columns. The independent predictions obtained from the model provided good representations of NAPL dissolution behavior and of total TCE/DCA mass removed, signifying model robustness. This indicates that for the complex three-dimensional model, explicit consideration of the larger scale factors that influenced immiscible-liquid dissolution in the flow cells allowed the use of a dissolution rate coefficient that represents only local-scale mass transfer processes. Conversely, the use of simpler models that did not explicitly consider the nonuniform immiscible-liquid distribution required the use of dissolution rate coefficients that are ∼3 orders of magnitude smaller than the values obtained from the columnexperiments. The rate coefficients associate with the simpler models represent composite or lumped coefficients that incorporate the effects of the larger scale dissolution precesses associated with the nonuniform immiscible-liquid distribution, which are not explicitly represented in the simpler models, as well as local-scale mass transfer. These results demonstrate that the local-scale dissolution rate coefficients, such as those obtained from column experiments, can be used in models to successfully predict dissolution and transport of immiscible-liquid constituents at larger scales when the larger scale factors influencing dissolution behavior are explicitly accounted for in the model.
• Costanza-Robinson, M. S., & Brusseau, M. L. (2002). Air-water interfacial areas in unsaturated soils: Evaluation of interfacial domains. Water Resources Research, 38(10), 131-1317.
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  Abstract: A gas-phase miscible-displacement method, using decane as an interfacial tracer, was used to measure air-water interfacial areas for a sand with water Contents ranging from ∼2% to 20%. The expected trend of decreasing interfacial areas with increasing water contents was observed. The maximum estimated interfacial area of 19,500 cm-1 appears reasonable given it is smaller than the measured surface area of the porous medium (60,888 cm-1). Comparison of the experimental data presented herein with literature data provided further insight into the characterization of the air-water intterface in unsaturated porous media. Specifically, comparison of interfacial areas measured using gas-phase versus aqueous-phase methods indicates that the gas-phase method generally yields larger interfacial areas than the aqueous-phase methods, even when accounting for differences in water content and physical properties of the porous media. The observations are consistent with proposed differences in interfacial accessibility of the aqueous- and gas-phase tracers. Evaluation of the data in light of functional interfacial domains, described herein, yields the hypothesis that aqueous interfacial tracers measure primarily air-water interfaces formed by "capillary water," while gas-phase tracers measure air-water interfaces formed by both capillary and surface-adsorbed (film) water. The gas- and aqueous-phase methods may each provide interfacial area information that is more relevant to specific problems of interest. For example, gas-phase interfacial area measurements may be most relevant to contaminant transport in unsaturated systems, where retention at the air-water interface may be significant. Conversely, the aqueous-phase methods may yield information with direct bearing on multiphase flow processes that are dominated by capillary-phase behavior.
• Costanza-Robinson, M. S., & Brusseau, M. L. (2002). Gas phase advection and dispersion in unsaturated porous media. Water Resources Research, 38(4), 71-710.
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  Abstract: Gas phase miscible displacement experiments were conducted to quantitatively investigate the advective and dispersive contributions to gas phase transport in unsaturated porous media over a range of soil water contents. Furthermore, the independence of measured dispersivity values was evaluated through comparison of nonreactive and reactive tracer transport. Methane was used as a nonreactive tracer, while difluoromethane (DFM) and trichloroethene (TCE) were used as reactive tracers. At soil water contents below 17%, measured dispersivity values are observed to be independent of the tracer compound and of the soil water content. Conversely, the dispersivities are tracer dependent at the highest soil water contents, wherein the values for DFM and TCE are 3 and 6 times larger than that of methane's, respectively. The significantly larger dispersivity values obtained for DFM and TCE are most likely due to rate-limited mass transfer of these compounds between the gas phase and soil water, which is not observed for methane because of its minimal water partitioning. The dispersivity values obtained here range between 0.3 and 3 cm and are similar to those reported in the literature. The results indicate that within a given "ideal transport" range, dispersivities measured at one soil water content with a given tracer may be representative of the same porous media system at other soil water contents and for other compounds.
• Srivastava, R., Sharma, P. K., & Brusseau, M. L. (2002). Spatial moments for reactive transport in heterogeneous porous media. Journal of Hydrologic Engineering, 7(4), 336-341.
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  Abstract: The transport of reactive chemicals through porous media is generally affected by multiple reactions with different rate constants. In this work, we investigate one-dimensional transport affected by rate-limited sorption, first-order mass transfer, and first-order transformation and derive analytical solutions for the spatial moments of the solute in the solution phase using an exponentially increasing dispersivity function to account for the spatial heterogeneity of hydraulic conductivity. Illustrative examples are used to discuss the effect of various rate constants on the travel distance, variance, and skewness. It is shown that the spatial heterogeneity of material properties can be satisfactorily accounted for by using an increasing macrodispersivity function. These solutions will be useful as a preliminary analysis tool for ascertaining the relative importance of various processes under given conditions. They may also be used to analyze the accuracy of various numerical techniques used for simulation of reactive transport through homogeneous and heterogeneous porous media.
• Yolcubal, I., Pierce, S. A., Maier, R. M., & Brusseau, M. L. (2002). Biodegradation during contaminant transport in porous media: V. The influence of growth and cell elution on microbial distribution. Journal of Environmental Quality, 31(6), 1824-1830.
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  PMID: 12469831;Abstract: This study investigated the interaction between microbial growth and cell elution, and their influence on resultant microbial distribution between the aqueous and solid phases during solute transport in a sandy, low-organic-carbon-content porous medium. Miscible displacement experiments were conducted with salicylate as the model compound, and with different initial conditions (e.g., substrate concentrations and cell densities) to attain various degrees of microbial growth. For each experiment, salicylate and dissolved oxygen concentrations as well as cell densities were monitored in the column effluent. Cell densities were also measured in the porous medium at the beginning and end of each experiment. Total microbial growth was determined in two ways, one based on a cell mass balance for the system and the other based on total amount of salicylate degraded. For conditions yielding a considerable amount of microbial growth, the majority of the biomass was associated with the aqueous phase (68-90%). Conversely, under minimal-growth conditions, most cells (approximately 60-70%) were attached to particle surfaces. Significant cell elution was observed for most conditions, the rate of which increased in the presence of the substrate. The results suggest that the increase in aqueous-phase cells observed for the experiments exhibiting the greatest growth is associated with the production of new cells, and that under appropriate conditions aqueous-phase biomass can contribute significantly to contaminant biodegradation.
• Blanford, W. J., Barackrnan, M. L., Boing, T. B., Klingel, E. J., Johnson, G. R., & Brusseau, M. L. (2001). Cyclodextrin-enhanced vertical flushing of a trichloroethene contaminated aquifer. Ground Water Monitoring and Remediation, 21(1), 58-66.
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  Abstract: Pilot-scale testing of an innovative ground water remediation technology was conducted in a source zone of a trichloroethene-contaminated Superfund site in Tucson, Arizona. The technology is designed to enhance the removal of low-solubility organic contaminants from heterogeneous sedimentary aquifers by using a dual-screened vertical circulation well to inject and extract solutions containing a complexing sugar (hydroxypropylbeta-cyclodextrin (HPCD]). Prior to initiating the pilot test, tracer tests were conducted to determine hydraulic characteristics of the vertical flow field and to evaluate trichloroethene-elution behavior during water flushing. The pilot test involved injecting approximately 4 m 3 of a 20% HPCD solution into the upper screened interval of the well and extracting from the lower screened interval. The results of the pilot test indicate that the cyclodextrin solution increased the rate of trichloroethene removal from the aquifer. The concentrations of trichloroethene in the ground water extracted from the lower screened interval of the well increased by a factor of three (∼750 μg/L) in the presence of the cyclodextrin pulse, compared to concentrations obtained during previous water flushing (∼250 μg/L). Furthermore, the concentration of trichloroethene in water collected from the circulation well under static conditions was reduced to 6% of the levels measured prior to the test.
• Boving, T. B., & Brusseau, M. L. (2001). Erratum: Solubilization and removal of residual trichloroethene from porous media: comparison of several solubilization agents (Journal of Contaminant Hydrology 42 (2000) (51-67) PII: S0169772299000777). Journal of Contaminant Hydrology, 49(1-2), 171-.
• Brusseau, M., Li, L., Yolcubal, I., Sandrin, S., Hu, M. Q., & Brusseau, M. L. (2001). Biodegradation during contaminant transport in porous media: 3. Apparent condition-dependency of growth-related coefficients. Journal of contaminant hydrology, 50(3-4).
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  The biodegradation of organic contaminants in the subsurface has become a major focus of attention, in part, due to the tremendous interest in applying in situ biodegradation and natural attenuation approaches for site remediation. The biodegradation and transport of contaminants is influenced by a combination of microbial and physicochemical properties and processes. The purpose of this paper is to investigate the impact of hydrodynamic residence time, substrate concentration, and growth-related factors on the simulation of contaminant biodegradation and transport, with a specific focus on potentially condition-dependent growth coefficients. Two sets of data from miscible-displacement experiments, performed with different residence times and initial solute concentrations, were simulated using a transport model that includes biodegradation described by the Monod nonlinear equations and which incorporates microbial growth and oxygen limitation. Two variations of the model were used, one wherein metabolic lag and cell transport are explicitly accounted for, and one wherein they are not. The magnitude of the maximum specific growth rates obtained from calibration of the column-experiment results using the simpler model exhibits dependency on pore-water velocity and initial substrate concentration (C0) for most cases. Specifically, the magnitude of micron generally increases with increasing pore-water velocity for a specific C0, and increases with decreasing C0 for a specific pore-water velocity. Conversely, use of the model wherein observed lag and cell elution are explicitly accounted for produces growth coefficients that are similar, both to each other and to the batch-measured value. These results illustrate the potential condition-dependency of calibrated coefficients obtained from the use of models that do not account explicitly for all pertinent processes influencing transport of reactive solutes.
• Li, L. i., Yolcubal, I., Sandrin, S., Hu, M. Q., & Brusseau, M. L. (2001). Biodegradation during contaminant transport in porous media: 3. Apparent condition-dependency of growth-related coefficients. Journal of Contaminant Hydrology, 50(3-4), 209-223.
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  PMID: 11523325;Abstract: The biodegradation of organic contaminants in the subsurface has become a major focus of attention, in part, due to the tremendous interest in applying in situ biodegradation and natural attenuation approaches for site remediation. The biodegradation and transport of contaminants is influenced by a combination of microbial and physicochemical properties and processes. The purpose of this paper is to investigate the impact of hydrodynamic residence time, substrate concentration, and growth-related factors on the simulation of contaminant biodegradation and transport, with a specific focus on potentially condition-dependent growth coefficients. Two sets of data from miscible-displacement experiments, performed with different residence times and initial solute concentrations, were simulated using a transport model that includes biodegradation described by the Monod nonlinear equations and which incorporates microbial growth and oxygen limitation. Two variations of the model were used, one wherein metabolic lag and cell transport are explicitly accounted for, and one wherein they are not. The magnitude of the maximum specific growth rates obtained from calibration of the column-experiment results using the simpler model exhibits dependency on pore-water velocity and initial substrate concentration (C0) for most cases. Specifically, the magnitude of μm generally increases with increasing pore-water velocity for a specific C0, and increases with decreasing C0 for a specific pore-water velocity. Conversely, use of the model wherein observed lag and cell elution are explicitly accounted for produces growth coefficients that are similar, both to each other and to the batch-measured value. These results illustrate the potential condition-dependency of calibrated coefficients obtained from the use of models that do not account explicitly for all pertinent processes influencing transport of reactive solutes. Copyright © 2001 Elsevier Science B.V.
• McCray, J. E., Bai, G., Maier, R. M., & Brusseau, M. L. (2001). Biosurfactant-enhanced solubilization of NAPL mixtures. Journal of Contaminant Hydrology, 48(1-2), 45-68.
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  PMID: 11291481;Abstract: Remediation of nonaqueous phase liquids (NAPLs) by conventional pump-and-treat methods (i.e., water flushing) is generally considered to be ineffective due to low water solubilities of NAPLs and to mass-transfer constraints. Chemical flushing techniques, such as surfactant flushing, can greatly improve NAPL remediation primarily by increasing the apparent solubility of NAPL contaminants. NAPLs at hazardous waste sites are often complex mixtures. However, the equilibrium and nonequilibrium mass-transfer characteristics between NAPL mixtures and aqueous surfactant solutions are not well understood. This research investigates the equilibrium solubilization behavior of two- and three-component NAPL mixtures (containing akylbenzenes) in biosurfactant solutions. NAPL solubilization is found to be ideal in water (i.e., obeys Raoult's Law), while solubilization in biosurfactant solutions was observed to be nonideal. Specifically, the relatively hydrophobic compounds in the mixture experienced solubility enhancements that were greater than those predicted by ideal enhanced solubilization theory, while the solubility enhancements for the relatively hydrophilic compounds were less than predicted. The degree of nonideality is shown to be a nonlinear function of the NAPL-phase mole fraction. Empirical relationships based on the NAPL-phase mole fraction and/or micelle-aqueous partition coefficients measured in single-component NAPL systems are developed to estimate values for the multicomponent partition coefficients. Empirical relationships that incorporate both the NAPL-phase mole fraction and single-component partition coefficients yield much improved estimates for the multicomponent partition coefficient. Copyright © 2001 Elsevier Science B.V.
• Oostrom, M., White, M. D., & Brusseau, M. L. (2001). Theoretical estimation of free and entrapped nonwetting-wetting fluid interfacial areas in porous media. Advances in Water Resources, 24(8), 887-898.
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  Abstract: Fluid-fluid interfacial areas play important roles in numerous subsurface processes such as dissolution, volatilization, and adsorption. Integral expressions have been derived to estimate both entrapped (discontinuous) and free (continuous) nonwetting fluid-wetting fluid specific interfacial areas in porous media. The expressions, compatible with widely used capillary head-saturation and entrapment models, require information on capillary head-saturation relation parameters, porosity, and fluid-pair interfacial tension. In addition, information on the maximum entrapped nonwetting fluid saturation as well as the main drainage branch reversal point for water and total liquid saturations is necessary to estimate entrapped fluid interfacial areas. Implementation of the interfacial area equations in continuum-based multifluid flow simulators is straightforward since no additional parameters are needed than those required by the simulators to complete the multifluid flow computations. A limited sensitivity analysis, based on experimentally obtained parameter values, showed that imposed variations resulted in logical and consistent changes in predicted specific interfacial areas for both entrapped and free nonwetting fluid-wetting fluid systems. A direct comparison with published experimental work to test the derived expressions was limited to free air-water systems and yielded reasonable results. Such comparisons are often not possible because of the lack of information given on retention parameters, and variables used to determine nonwetting fluid entrapment. This contribution is dedicated to John W. Cary. © 2001 Elsevier Science Ltd. All rights reserved.
• Sandrin, S. K., Jordan, F. L., Maier, R. M., & Brusseau, M. L. (2001). Biodegradation during contaminant transport in porous media: 4. Impact of microbial lag and bacterial cell growth. Journal of Contaminant Hydrology, 50(3-4), 225-242.
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  PMID: 11523326;Abstract: Miscible-displacement experiments were conducted to examine the impact of microbial lag and bacterial cell growth on the transport of salicylate, a model hydrocarbon compound. The impacts of these processes were examined separately, as well as jointly, to determine their relative effects on biodegradation dynamics. For each experiment, a column was packed with porous medium that was first inoculated with bacteria that contained the NAH plasmid encoding genes for the degradation of naphthalene and salicylate, and then subjected to a step input of salicylate solution. The transport behavior of salicylate was non-steady for all cases examined, and was clearly influenced by a delay (lag) in the onset of biodegradation. This microbial lag, which was consistent with the results of batch experiments, is attributed to the induction and synthesis of the enzymes required for biodegradation of salicylate. The effect of microbial lag on salicylate transport was eliminated by exposing the column to two successive pulses of salicylate, thereby allowing the cells to acclimate to the carbon source during the first pulse. Elimination of microbial lag effects allowed the impact of bacterial growth on salicylate transport to be quantified, which was accomplished by determining a cell mass balance. Conversely, the impact of microbial lag was further investigated by performing a similar double-pulse experiment under no-growth conditions. Significant cell elution was observed and quantified for all conditions/systems. The results of these experiments allowed us to differentiate the effects associated with microbial lag and growth, two coupled processes whose impacts on the biodegradation and transport of contaminants can be difficult to distinguish. Copyright © 2001 Elsevier Science B.V.
• Boving, T. B., & Brusseau, M. L. (2000). Solubilization and removal of residual trichloroethene from porous media: Comparison of several solubilization agents. Journal of Contaminant Hydrology, 42(1), 51-67.
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  Abstract: The development of improved methods for remediation of contaminated subsurface systems has emerged as a significant environmental priority. One technology that appears to have considerable promise involves the use of solubilization-enhancing agents, such as surfactants, cosolvents, dissolved organic matter (DOM), and complexing agents, to promote removal of immiscible-liquid and sorbed phase organic contaminants. We examined the use of six flushing agents, i.e., two anionic surfactants, two complexing agents (cyclodextrins), a humic acid, and an alcohol, for solubilizing and removing residual-phase immiscible liquid from porous media. The results of batch experiments conducted to measure the degree of trichloroethene (TCE) solubilization induced by these agents show that the solubility of TCE was enhanced between 3 and 57 times depending on the flushing agent. Column experiments were conducted to compare water and agent-enhanced flushing of Borden sand containing residual saturations of TCE. As expected, the total flushing volume necessary to remove the residual saturation was reduced substantially in the presence of all applied agents. The relative effectiveness of the agents varied based on the method of evaluation. On a mass-efficiency basis, SDS outperformed all other agents, whereas DOM provided the best performance on a molar-efficiency basis. Copyright (C) 2000 Elsevier Science B.V.
• Brusseau, M. L., Nelson, N. T., Oostrom, M., Zhang, Z., Johnson, G. R., & Wietsma, T. W. (2000). Influence of heterogeneity and sampling method on aqueous concentrations associated with NAPL dissolution. Environmental Science and Technology, 34(17), 3657-3664.
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  Abstract: The purpose of this work is to examine the effects of nonuniform distributions of nonaqueous-phase liquid (NAPL) saturation, porous-media heterogeneity, and sampling method on the magnitude of aqueous concentrations measured under dynamic conditions of flow and transport. Dissolution experiments were conducted in an intermediate-scale flow cell packed with sand in which two zones of residual trichloroethene (TCE) saturation were placed. One was created in the same medium-grained sand as used for the flow cell matrix (zone 2), and the other was created in finer sand (zone 1). Aqueous samples were collected using depth-specific sampling ports, vertically integrated sampling ports, and at the fully screened extraction well. A dual-energy γ-radiation system was used to measure TCE saturation before and after the experiment. The results indicate that mass removal occurred relatively uniformly across the upgradient edge of zone 2 and continued progressively along the longitudinal axis of the zone throughout the course of flushing. Conversely, mass removal was confined primarily to the perimeter of zone 1. The magnitude of the aqueous-phase TCE concentrations varied as a function of location and sampling method. The concentrations measured at the point-sampling ports downgradient of zone 2 were close to the value of aqueous solubility. Conversely, the concentrations measured at the point-sampling ports downgradient of zone 1 were about one-fourth of solubility. The TCE concentrations measured at the vertically integrated ports and at the extraction well were significantly less than the concentrations measured at the point-sampling ports. Given that substantial TCE saturation remained at the end of the experiment, the less than solubility concentrations observed for zone 1 and for the extraction well appear to reflect in part a steady-state dynamic equilibrium with the physical heterogeneity-induced nonuniform flow field. The less than solubility concentrations, especially for the integrated ports and the extraction well, were also influenced significantly by sampling-associated dilution related to the nonuniform NAPL distribution. These observations are supported by the results of a nonreactive tracer test, by the results of a dye-tracer test, and by a quantitative analysis of flow and tracer transport obtained using a three-dimensional mathematical model.
• Cain, R. B., Johnson, G. R., McCray, J. E., Blanford, W. J., & Brusseau, M. L. (2000). Partitioning tracer tests for evaluating remediation performance. Ground Water, 38(5), 752-761.
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  Abstract: Researchers are applying a range of partitioning tracer tests for the identification and measurement of nonaqueous phase liquid (NAPL) saturations in contaminated aquifers. Studies investigating the performance of such systems were conducted at Hill Air Force Base, UT. Tests enacted at this facility were carried out in two hydraulically isolated test cells of an aquifer polluted with light nonaqueous phase liquids. Testing activities were conducted both before and after two remediation regimes, namely a complexing sugar flush (CSF) and a recirculating in-well aeration (IWA) system. Analyses of the breakthrough curves identified the presence of an immiscible phase. Techniques used to calculate remediation efficiencies for both of the tested cells are reviewed.
• Costanza, M. S., & Brusseau, M. L. (2000). Contaminant vapor adsorption at the gas-water interface in soils. Environmental Science and Technology, 34(1), 1-11.
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  Abstract: There is evidence to suggest that the gas-water interface serves as an important retention domain for volatile organic compounds (VOCs) in vadose-zone soil. Moreover, vapor adsorption at the gas-water interface may represent the dominant retention mechanism under certain conditions. In general, vapor-phase interfacial adsorption is most significant for low organic matter soils at intermediate water contents. Among nonpolar compounds, those with low saturated vapor pressure have the greatest tendency for interfacial adsorption, as represented by higher interfacial sorption coefficients, K(IA). Although polar compounds may have greater tendency to adsorb at the interface than nonpolar compounds, the high aqueous solubility of polar compounds may limit the relative importance of interfacial sorption to total contaminant retention. The magnitude of interfacial retention is controlled by the specific interfacial area, A(IA), as well as by K(IA). Validated methods for measuring A(IA) are currently lacking. However, three promising methods for measuring A(IA) in soils have been proposed. Preliminary results indicate that the three methods are complimentary in terms of the type of information derived, as well as their applicability for different water content ranges and varying scales (e.g., laboratory vs field).
• McCray, J. E., Boving, T. B., & Brusseau, M. L. (2000). Cyclodextrin-enhanced solubilization of organic contaminants with implications for aquifer remediation. Ground Water Monitoring and Remediation, 20(1), 94-103.
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  Abstract: Reagents that enhance the aqueous solubility of non-aqueous phase organic liquid (NAPL) contaminants are under investigation for use in enhanced subsurface remediation technologies. Cyclodextrin, a glucose-based molecule, is such a reagent. In this paper, laboratory experiments and numerical model simulations are used to evaluate and understand the potential remediation performance of cyclodextrin. Physical properties of cyclodextrin solutions such as density, viscosity, and NAPL-aqueous interfacial tension are measured. Our analysis indicates that no serious obstacles exist related to fluid properties that would prevent the use of cyclodextrin solutions for subsurface NAPL remediation. Cyclodextrin-enhanced solubilization for a large suite of typical ground water contaminants is measured in the laboratory, and the results are related to the physicochemical properties of the organic compounds. The most-hydrophobic contaminants experience a larger relative solubility enhancement than the less-hydrophobic contaminants but have lower aqueous-phase apparent solubilities. Numerical model simulations of enhanced-solubilization flushing of NAPL-contaminated soil demonstrate that the more-hydrophilic compounds exhibit the greatest mass-removal rates due to their greater apparent solubilities, and thus are initially more effectively removed from soil by enhanced-solubilization-flushing reagents. However, the relatively more hydrophobic contaminants exhibit a greater improvement in contaminant mass-removal (compared with water flushing) than that exhibited for the relatively hydrophilic contaminants.
• Noordman, W. H., Brusseau, M. L., & Janssen, D. B. (2000). Adsorption of a multicomponent rhamnolipid surfactant to soil. Environmental Science and Technology, 34(5), 832-838.
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  Abstract: The adsorption of rhamnolipid, a multicomponent biosurfactant with potential application in soil remediation, to two sandy soils was investigated using batch and column studies. The surfactant mixture contained six anionic components differing in lipid chain length and number of rhamnose moieties. Batch adsorption experiments indicated that the overall adsorption isotherms of total surfactant and of the individual components leveled off above a concentration at which micelles were formed. Column experiments showed that the retardation factors for the total surfactant and for the individual components decreased with increasing influent concentration. Extended tailing was observed in the distal portion of the surfactant breakthrough curve. The concentration-dependent retardation factors and the extended tailing are in accordance with the nonlinear (concave) adsorption isotherms found in the batch adsorption studies. The more hydrophobic rhamnolipid components were preferentially adsorbed, but adsorption was not correlated with the organic carbon content of the soil. This suggests that adsorption of rhamnolipid to soil is not a partitioning process but mainly an interfacial adsorption process.
• Yolcubal, I., Piatt, J. J., Pierce, S. A., Brusseau, M. L., & Maier, R. M. (2000). Fiber optic detection of in situ lux reporter gene activity in porous media: System design and performance. Analytica Chimica Acta, 422(2), 121-130.
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  Abstract: A luminescence detection system is described that couples a genetically engineered bioluminescent reporter organism and fiber optic technology for monitoring in situ reporter gene activity in porous media under dynamic conditions. The reporter bacterium used was Pseudomonas putida RB1353, which carries plasmids NAH7 and pUTK9 that encode genes for salicylate degradation (nah) and luminescence (lux) that are regulated by the same promoter. The system can be used to examine the relationship between microbial activity and the resultant impact on biodegradation and transport of salicylate in porous media. Several batch and column experiments were conducted to analyze the performance of the fiber optic detection system. Batch studies showed that the fiber optic response in liquid cultures was linearly correlated to a calibrated system response using a liquid scintillation counter in the single photon counting mode. In column studies, it was demonstrated that decreases in salicylate and dissolved oxygen concentrations associated with biodegradation were correlated with an increase in luminescence response. The maximum luminescence given off by the reporter organism was linearly related to salicylate concentration. These results indicate that the fiber optic system can be used to monitor microbial activity under dynamic conditions. This system allows rapid, real-time, and non-destructive measurements of luminescence from a specific lux reporter microbial population in porous media. (C) 2000 Elsevier Science B.V.
• Zhen, L. i., & Brusseau, M. L. (2000). Nonideal transport of reactive solutes in heterogeneous porous media 6. Microscopic and macroscopic approaches for incorporating heterogeneous rate-limited mass transfer. Water Resources Research, 36(10), 2853-2867.
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  Abstract: Two major approaches have been used to incorporate heterogeneous ratelimited mass transfer into mathematical models for solute transport. One focuses on processes operative at the microscopic scale and associated grain-scale heterogeneity, while the other stresses the macroscopic variability of the medium and the field-scale behavior of solute transport. In this paper, we examine the conceptual framework and model formulation of these two approaches in an attempt to evaluate potential commonality. Numerical solvers are developed for both sets of governing equations, and the performance of these two models is tested for two systems, each incorporating one of two types of mass transfer mechanisms. The results show that despite differences in conceptualization and formulation, the models produce comparable behavior for smallerscale systems. However, greater deviations are observed at larger scales. This suggests that caution should be exercised when using mathematical modeling for elucidating the specific processes that may be influencing reactive-solute transport for a given system. We also evaluate the impact of microscopic-scale mass transfer heterogeneity on field-scale transport in systems for which hydraulic conductivity is spatially variable. The results show that inclusion of locally heterogeneous mass transfer does not appear to significantly influence the mean transport behavior for systems with field-scale heterogeneity. However, it does appear to influence low-concentration tailing. For simulations of reactive transport over extended distances, models with locally heterogeneous mass transfer may 'preserve' the nonequilibrium effects associated with rate-limited mass transfer better than models incorporating locally uniform mass transfer when both pore-scale and field-scale heterogeneity coexist.
• Blanford, W. J., Klingel, E. J., Johnson, G. R., Cain, R. B., Enfield, C., & Brusseau, M. L. (1999). Performance Assessment of In-Well Aeration for the Remediation of an Aquifer Contaminated by a Multicomponent Immiscible Liquid. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 167-182.
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  Abstract: A pilot-scale test to evaluate the performance of a vertical recirculation well equipped with an in-well air stripper was conducted at Hill AFB, Utah, in an aquifer contaminated with petroleum and chlorinated solvents. During the two months of operation, the air stripping system was found to remove more than 26% of the combined mass of ten representative contaminants from water passing through the well. The cell-wide performance was evaluated by comparing the contaminant concentrations for aquifer core samples collected before and after the test and by comparing the average immiscible liquid saturations determined with partitioning tracer tests conducted before and after operation. The net magnitude of remediation was low (
• Blanford, W. J., Klingel, E. J., Johnson, G. R., Cain, R. B., Enfield, C., & Brusseau, M. L. (1999). Performance assessment of in-well aeration for the remediation of an aquifer contaminated by a multicomponent immiscible liquid. ACS Symposium Series, 725, 167-181.
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  Abstract: A pilot-scale test to evaluate the performance of a vertical recirculation well equipped with an in-well air stripper was conducted at Hill AFB, Utah, in an aquifer contaminated with petroleum and chlorinated solvents. During the two months of operation, the air stripping system was found to remove more than 26% of the combined mass often representative contaminants from water passing through the well. The cell-wide performance was evaluated by comparing the contaminant concentrations for aquifer core samples collected before and after the test and by comparing the average immiscible liquid saturations determined with partitioning tracer tests conducted before and after operation. The net magnitude of remediation was low (
• Boving, T. B., Wang, X., & Brusseau, M. L. (1999). Cyclodextrin-enhanced solubilization and removal of residual-phase chlorinated solvents from porous media. Environmental Science and Technology, 33(5), 764-770.
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  Abstract: The development of improved methods for remediation of contaminated aquifers has emerged as a significant environmental priority. One technology that appears to have considerable promise involves the use of solubilization agents such as surfactants and cosolvents for enhancing the removal of residual phase immiscible liquids. We examined herein the use of cyclodextrin, a glucose-based molecule, for solubilizing and removing residual-phase immiscible liquid from porous media. Batch experiments were conducted to measure the degree of trichloroethene (TCE) and tetrachloroethene (PCE) solubilization induced by hydroxypropyl-β- cyclodextrin (HPCD) and methyl-β-cyclodextrin (MCD). These studies revealed that the solubilities of TCE and PCE were enhanced by up to 9.5 and 36.0 times, respectively. Column experiments were conducted to compare water and cyclodextrin-enhanced flushing of Borden sand containing residual saturations of TCE and PCE. The results indicate that solubilization and mass removal were enhanced substantially with the use of cyclodextrins. The effluent concentrations during the steady-state phase of the HPCD (5% and 10%) and MCD (5%) flushing experiments were close to the apparent solubilities measured with the batch experiments, indicating equilibrium concentrations were maintained during the initial phase of cyclodextrin flushing. Mobilization was observed for only the TCE-MCD (5% and 10%) and PCE-5% MCD experiments.
• Brusseau, M. L., & Srivastava, R. (1999). Nonideal transport of reactive solutes in heterogeneous porous media. 4. Analysis of the Cape Cod natural-gradient field experiment. Polygraph International, 1113-1125.
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  Abstract: The quantitative analysis of the transport of lithium at Cape Cod is presented which identifies the factors that contributed significantly to its observed nonideal transport. The transport behavior observed during the first 250 days, corresponding to a transport distance of 60 m, was predicted reasonably well by the simulation that incorporated spatially variable hydraulic conductivity. The results of the analysis suggest that nonlinear sorption and variable water chemistry are the primary factors responsible for the nonuniform displacement of the lithium plume, with rate-limited sorption/desorption having minimal impact.
• Brusseau, M. L., & Srivastava, R. (1999). Nonideal transport of reactive solutes in heterogeneous porous media. 4. Analysis of the Cape Cod natural-gradient field experiment. Water Resources Research, 35(4), 1113-1125.
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  Abstract: One of the largest field studies of reactive-solute transport is the natural-gradient experiment conducted at Cape Cod from 1985 to 1988. Major findings regarding the transport behavior of the reactive solute (lithium) were that the rate of plume displacement decreased with time (temporal increase in effective retardation), the degree of longitudinal spreading was much greater than that observed for bromide for an equivalent travel distance, and the plume was asymmetric, with maximum concentrations located near the leading edges. The objective of our work was to quantitatively analyze the transport of lithium and to attempt to identify the factor or factors that contributed significantly to its observed nonideal transport. We used a mathematical model that accounted for several transport factors, including spatially variable hydraulic conductivity and spatially variable, nonlinear, rate-limited sorption, with all parameter values obtained independently. The transport behavior observed during the first 250 days, corresponding to a transport distance of 60 m, was predicted reasonably well by the simulation that incorporated spatially variable hydraulic conductivity; nonlinear, rate-limited, spatially variable sorption; and uniform water chemistry. However, the larger degree of deceleration observed during the latter stage of the experiment (the final 20 m) was not. The larger deceleration was successfully simulated by increasing 3-fold the mean sorption capacity of the latter portion of the transport domain. Such a change in sorption capacity is consistent with the potential impact on lithium sorption of measured changes in water chemistry (e.g., pH increase, reduction in resident Zn) that occur in the zone through which the lithium plume traversed. The results of the analyses suggest that nonlinear sorption and variable water chemistry may have been primary factors responsible for the nonuniform displacement of the lithium plume, with rate-limited sorption/desorption having minimal impact. In addition, the asymmetry of the plume appears to have been caused primarily by nonlinear sorption, whereas the enhanced longitudinal spreading appears to have been caused by the combined influences of spatially variable hydraulic conductivity and sorption, nonlinear sorption, and rate-limited sorption/desorption. A comparison of the results of this analysis to those we obtained from an analysis of the Borden natural-gradient study reveals several similarities regarding the transport of reactive contaminants at the field scale.
• Brusseau, M. L., Gierke, J. S., & Sabatini, D. A. (1999). Field Demonstrations of Innovative Subsurface Remediation and Characterization Technologies: Introduction. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 2-5.
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  Abstract: Groundwater pollution has become one of our most pervasive environmental problems, and remediating sites with contaminated groundwater has proven to be a formidable challenge. Remediation efforts are often limited by the complexity of the subsurface environment, and by our lack of knowledge of that environment. Recent research has focused on enhancing our understanding of the complex subsurface environment and on developing innovative technologies capable of handling these complexities. An important step in the evolution of a new technology is going beyond well-controlled laboratory experiments to testing the technology at the field scale (i.e., real world). The purpose of this volume is to present evaluations of selected innovative technologies that have undergone field demonstration testing. This volume also reports on recent advances in subsurface characterization techniques that are critical to the proper design of all technologies, and that can help assess the performance of these technologies.
• Brusseau, M. L., Gierke, J. S., & Sabatini, D. A. (1999). Field demonstrations of innovative subsurface remediation and characterization technologies: Introduction. ACS Symposium Series, 725, 2-5.
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  Abstract: Groundwater pollution has become one of our most pervasive environmental problems, and remediating sites with contaminated groundwater has proven to be a formidable challenge. Remediation efforts are often limited by the complexity of the subsurface environment, and by our lack of knowledge of that environment. Recent research has focused on enhancing our understanding of the complex subsurface environment and on developing innovative technologies capable of handling these complexities. An important step in the evolution of a new technology is going beyond well-controlled laboratory experiments to testing the technology at the field scale (i.e., real world). The purpose of this volume is to present evaluations of selected innovative technologies that have undergone field demonstration testing. This volume also reports on recent advances in subsurface characterization techniques that are critical to the proper design of all technologies, and that can help assess the performance of these technologies.
• Brusseau, M. L., Hu, M. Q., Wang, J., & Maier, R. M. (1999). Biodegradation during contaminant transport in porous media. 2. The influence of physicochemical factors. Environmental Science and Technology, 33(1), 96-103.
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  Abstract: The biodegradation of contaminants in the subsurface has become a topic of great interest. In systems wherein biodegradation is coupled with transport, the magnitude and rate of biodegradation is influenced not only by microbial properties but also by physicochemical properties. The purpose of this work is to systematically evaluate the impact of coupled physicochemical factors (residence time, substrate concentration, and electron-acceptor concentration) on the biodegradation of contaminants during transport in porous media. A suite of miscible-displacement experiments was conducted with different residence times and initial contaminant concentrations, using a petroleum-contaminated aquifer material and benzoate as a model compound. The results were evaluated using a framework developed from a mathematical analysis of the nondimensional parameters that control biodegradation during transport. The results show that the type of transport behavior observed is dependent upon system conditions and is predictable using the controlling- parameter approach. For benzoate, which is a relatively labile compound, transport was measurably influenced by biomass growth under most conditions tested, albeit to different extents. The exceptions occurred when either the substrate or oxygen (electron acceptor) concentrations were limiting. The results obtained from this study should improve our understanding of the coupled influence of residence time, substrate concentration, and microbial properties on the biodegradation of contaminants during transport in the subsurface.
• Brusseau, M. L., Hu, Q., Nelson, N. T., & Cain, R. B. (1999). A Diffusive Tracer-Test Method for Investigating the Influence of Mass Transfer Processes on Field-Scale Solute Transport. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 251-264.
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  Abstract: The purpose of this work is to illustrate the utility of the diffusive tracer-test method for investigating the influence of diffusion-mediated processes on solute transport at the field scale. The diffusive tracer test involves the use of a suite of tracers of various sizes (i.e., diffusivities), and is based on the hypothesis that diffusion-mediated processes will generally be sensitive to the aqueous diffusivity of the solute. Hence, the transport of tracers with different diffusivities should be different when diffusion-mediated processes are important. The method was successfully applied to a field site representative of alluvial aquifer systems.
• Brusseau, M. L., Hu, Q., Nelson, N. T., & Cain, R. B. (1999). A diffusive tracer-test method for investigating the influence of mass transfer processes on field-scale solute transport. ACS Symposium Series, 725, 251-264.
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  Abstract: The purpose of this work is to illustrate the utility of the diffusive tracer-test method for investigating the influence of diffusion-medicated processes on solute transport at the field scale. The diffusive tracer test involves the use of a suite of tracers of various sizes (i.e., diffusivities), and is based on the hypothsis that diffusion-mediated processes will generally be sensitive to the aqueous diffusivity of the solute. Hence, the transport of tracers with different diffusivities should be different when diffusion-mediated processes are important. The method was successfully applied to a field site representative of alluvial aquifer systems.
• Brusseau, M. L., McCray, J. E., Johnson, G. R., Wang, X., Wood, A. L., & Enfield, C. (1999). Field Test of Cyclodextrin for Enhanced In-Situ Flushing of Multiple- Component Immiscible Organic Liquid Contamination: Project Overview and Initial Results. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 118-135.
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  Abstract: The purpose of this paper is to present an overview and the initial results of a pilot-scale experiment designed to test the use of cyclodextrin for enhanced in-situ flushing of an aquifer contaminated by immiscible liquid. This is the first field test of this technology, termed a complexing sugar flush (CSF). The field test was conducted within a solvent and fuel disposal site at Hill Air Force Base, UT. The cyclodextrin solution increased the aqueous concentrations of all the target contaminants to values from about 100 to more than 20 000 times the concentrations obtained during the water flush conducted prior to the CSF. Concomitantly, the CSF greatly enhanced the rate of mass removal during the 8 pore-volume flush, which resulted in a 41% reduction in contaminant mass. Based on these results, it is clear that the CSF technology was successful in enhancing the remediation of the immiscible-liquid contaminated site. There are several attributes of cyclodextrin that in some situations may offer advantages compared to using surfactants or cosolvents for solubilization-based enhanced flushing.
• Brusseau, M. L., McCray, J. E., Johnson, G. R., Wang, X., Wood, A. L., & Enfield, C. (1999). Field test of cyclodextrin for enhanced in-situ flushing of multiple-component immiscible organic liquid contamination: Project overview and initial results. ACS Symposium Series, 725, 118-135.
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  Abstract: The purpose of this paper is to present an overview and the initial results of a pilot-scale experiment designed to test the use of cyclodextrin for enhanced in-situ flushing of an aquifer contaminated by immiscible liquid. This is the first field test of this technology, termed a complexing sugar flush (CSF). The field test was conducted within a solvent and fuel disposal site at Hill Air Force Base, UT. The cyclodextrin solution increased the aqueous concentrations of all the target contaminants to values from about 100 to more than 20000 times the concentrations obtained during the water flush conducted prior to the CSF. Concomitantly, the CSF greatly enhanced the rate of mass removal during the 8 pore-volume flush, which resulted in a 41% reduction in contaminant mass. Based on these results, it is clear that the CSF technology was successful in enhancing the remediation of the immiscible-liquid contaminated site. There are several attributes of cyclodextrin that in some situations may offer advantages compared to using surfactants or cosolvents for solubilization-based enhanced flushing.
• Brusseau, M. L., Nelson, N. T., & Cain, R. B. (1999). The Partitioning Tracer Method for In-Situ Detection and Quantification of Immiscible Liquids in the Subsurface. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 208-225.
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  Abstract: Conducting risk assessments and developing remediation programs for contaminated sites requires knowledge of the occurrence and distribution of immiscible liquids in the subsurface. Current 'point-sampling' characterization methods, such as analysis of soil gas, core sampling, cone penetrometer testing, and monitor-well sampling, are often not capable of providing the amount of data required for effective +risk assessment or remediation system design, without a cost-prohibitive number of samples. The purpose of this work is to discuss an alternative method, the partitioning tracer test, for measuring the quantity and distribution of immiscible liquid in the subsurface. The basis for this method will be briefly reviewed, followed by a discussion of its implementation. Practical considerations as well as limitations of the method will also be discussed. Application of the method will be illustrated for a site contaminated with a multiple-component immiscible liquid.
• Brusseau, M. L., Nelson, N. T., & Cain, R. B. (1999). The partitioning tracer method for in-situ detection and quantification of immiscible liquids in the subsurface. ACS Symposium Series, 725, 208-225.
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  Abstract: Conducting risk assessments and developing remediation programs for contaminated sites requires knowledge of the occurrence and distribution of immiscible liquids in the subsurface. Current "point-sampling" characterization methods, such as analysis of soil gas, core sampling, cone penetrometer testing, and monitor-well sampling, are often not capable of providing the amount of data required for effective +risk assessment or remediation system design, without a cost-prohibitive number of samples. The purpose of this work is to discuss an alternative method, the partitioning tracer test, for measuring the quantity and distribution of immiscible liquid in the subsurface. The basis for this method will be briefly reviewed, followed by a discussion of its implementation. Practical considerations as well as limitations of the method will also be discussed. Application of the method will be illustrated for a site contaminated with a multiple-component immiscible liquid.
• Brusseau, M. L., Piatt, J. J., Wang, J., & Hu, M. Q. (1999). A Biotracer Test for Characterizing the In-Situ Biodegradation Potential Associated with Subsurface Systems. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 240-250.
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  Abstract: Evaluating the feasibility of using intrinsic or accelerated in-situ bioremediation for a specific site requires a determination of the in-situ biodegradation potential of the target contaminants in the contaminated zone, which is a very difficult task. The purpose of this paper is to introduce a field-scale, controlled-release approach based on the use of a biodegradation tracer test. This method entails conducting a tracer experiment with one or more compounds whose biodegradation characteristics are well known. The biotracer test can be used to: (1) evaluate the general biodegradation potential associated with the zone of interest, (2) evaluate the response of the system to perturbations such as oxygen addition, and (3) evaluate the biodegradation potential for a specific contaminant. The utility of the biotracer test for the first application is illustrated with a test conducted at a field site contaminated by jet fuel. The results of the experiments indicate that it is possible to characterize the degradation potential of a selected site using biotracers. This method may, therefore, be a useful addition to our arsenal of methods for evaluating the feasibility and performance of in situ bioremediation.
• Brusseau, M. L., Piatt, J. J., Wang, J., & Hu, M. Q. (1999). A biotracer test for characterizing the in-situ biodegradation potential associated with subsurface systems. ACS Symposium Series, 725, 240-250.
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  Abstract: Evaluating the feasibility of using intrinsic or accelerated in-situ bioremediation for a specific site requires a determination of the in-situ biodegradation potential of the target contaminants in the contaminated zone, which is a very difficult task. The purpose of this paper is to introduce a field-scale, controlled-release approach based on the use of a biodegradation tracer test. This method entails conducting a tracer experiment with one or more compounds whose biodegradation characteristics are well known. The biotracer test can be used to: (1) evaluate the general biodegradation potential associated with the zone of interest, (2) evaluate the response of the system to perturbations such as oxygen addition, and (3) evaluate the biodegradation potential for a specific contaminant. The utility of the biotracer test for the first application is illustrated with a test conducted at a field site contaminated by jet fuel. The results of the experiments indicate that it is possible to characterize the degradation potential of a selected site using biotracers. This method may, therefore, be a useful addition to our arsenal of methods for evaluating the feasibility and performance of in situ bioremediation.
• Brusseau, M. L., Rohrer, J. W., Decker, T. M., Nelson, N. T., & Linderfelt, W. R. (1999). Contaminant Transport and Fate in a Source Zone of a Chlorinated-Solvent Contaminated Superfund Site: Overview and Initial Results of an Advanced Site Characterization Project. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 265-281.
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  Abstract: An advanced site characterization project is being conducted at a chlorinated-solvent contaminated Superfund site to help improve the effectiveness of the remediation program. As a part of this project, two forced-gradient tracer tests were conducted to characterize the transport behavior of bromide and resident trichloroethene and dichloroethene in the aquifer underlying a contaminant source zone. The results indicate significant vertical spatial variability of hydraulic (hydraulic conductivity) and chemical (contaminant concentrations) variables over the 6 m thick aquifer zone. The tracer experiments provide a direct demonstration of the influence of subsurface heterogeneity on water flow, and its possible impact on the efficient removal of trichloroethene and dichloroethene by pump and treat. Extensive elution tailing and rebound were observed for trichloroethene and dichloroethene during the experiments, which indicate the presence of a significant mass of contaminant whose transfer to the advecting water is rate limited. This mass could be sorbed to aquifer material, located within low permeability zones, associated with an immiscible-liquid phase, or some combination thereof. Identification of the factors that control contaminant mass removal is critical for a complete, successful cleanup of the site. Current and future research associated with this site targets these issues.
• Brusseau, M. L., Rohrer, J. W., Decker, T. M., Nelson, N. T., & Linderfelt, W. R. (1999). Contaminant transport and fate in a source zone of a chlorinated-solvent contaminated superfund site: Overview and initial results of an advanced site characterization project. ACS Symposium Series, 725, 265-281.
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  Abstract: An advanced site characterization project is being conducted at a chlorinated-solvent contaminated Superfund site to help improve the affectiveness of the remediation program. As a part of this project, two forced-gradient tracer tests were conducted to characterize the transport behavior of bromide and resident trichloroethene and dichloroethene in the aquifer underlying a contaminant source zone. The results indicate significant vertical spatial variability of hydraulic (hydraulic conductivity) and chemical (contaminant concentration) variables over the 6 m thick aquifer zone. The tracer experiments provide a direct demonstration of the influence of subsurface heterogeneity on water flow, and its possible impact on the efficient removal of trichloroethene and dichloroethene by pump and treat. Extensive elution tailing and rebound were observed for trichloroethene and dichloroethene during the experiments, which indicate the presence of a significant mass of contaminant whose transfer to the advecting water is rate limited. This mass could be sorbed to aquifer material, located within low permeability zones, associated with an immiscible-liquid phase, or some combination thereof. Identification of the factors that control contaminant mass removal is critical for a complete, successful cleanup of the site. Current and future research associated with this site targets these issues.
• Brusseau, M. L., Xie, L. H., & Li, L. i. (1999). Biodegradation during contaminant transport in porous media: 1. Mathematical analysis of controlling factors. Journal of Contaminant Hydrology, 37(3-4), 269-293.
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  Abstract: Interest in coupled biodegradation and transport of organic contaminants has expanded greatly in the past several years. In a system in which biodegradation is coupled with solute transport, the magnitude and rate of biodegradation is influenced not only by properties of the microbial population and the substrate, but also by hydrodynamic properties (e.g., residence time, dispersivity). By nondimensionalizing the coupled-process equations for transport and nonlinear biodegradation, we show that transport behavior is controlled by three characteristic parameters: the effective maximum specific growth rate, the relative half-saturation constant, and the relative substrate-utilization coefficient. The impact on biodegradation and transport of these parameters, which constitute various combinations of factors reflecting the influences of biotic and hydraulic properties of the system, are examined numerically. A type-curve diagram based on the three characteristic parameters is constructed to illustrate the conditions under which steady and non-steady transport is observed, and the conditions for which the linear, first-order approximation is valid for representing biodegradation. The influence of constraints to microbial growth and substrate utilization on contaminant transport is also briefly discussed. Additionally, the impact of biodegradation, with and without biomass growth, on spatial solute distribution and moments is examined. Copyright (C) 1999 Elsevier Science B.V.
• DiGiulio, D. C., Ravi, V., & Brusseau, M. L. (1999). Evaluation of mass flux to and from ground water using a vertical flux model (VFLUX): Application to the soil vacuum extraction closure problem. Ground Water Monitoring and Remediation, 19(2), 96-104.
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  Abstract: Site closure for soil vacuum extraction (SVE) application typically requires attainment of specified soil concentration standards based on the premise that mass flux from the vadose zone to ground water not result in levels exceeding maximum contaminant levels (MCLs). Unfortunately, realization of MCLs in ground water may not be attainable at many sites. This results in soil remediation efforts that may be in excess of what is necessary for future protection of ground water and soil remediation goals which often cannot be achieved within a reasonable time period. Soil venting practitioners have attempted to circumvent these problems by basing closure on some predefined percent total mass removal, or an approach to a vapor concentration asymptote. These approaches, however, are subjective and influenced by venting design. We propose an alternative strategy based on evaluation of five components: (1) site characterization, (2) design, (3) performance monitoring, (4) rate-limited vapor transport, and (5) mass flux to and from ground water. Demonstration of closure is dependent on satisfactory assessment of all five components. The focus of this paper is to support mass flux evaluation. We present a plan based on monitoring of three subsurface zones and develop an analytical one-dimensional vertical flux model we term VFLUX. VFLUX is a significant improvement over the well-known numerical one-dimensional model, VLEACH, which is often used for estimation of mass flux to ground water, because it allows for the presence of nonaqueous phase liquids (NAPLs) in soil, degradation, and a time-dependent boundary, condition at the water table interface. The time-dependent boundary condition is the centerpiece of our mass flux approach because it dynamically links performance of ground water remediation to SVE closure. Progress or lack of progress in ground water remediation results in either increasingly or decreasingly stringent closure requirements, respectively.
• McCray, J. E., Bryan, K. D., Cain, R. B., Johnson, G. R., Blanford, W. J., & Brusseau, M. L. (1999). Field Test of Cyclodextrin for Enhanced In-Situ Flushing of Multiple- Component Immiscible Organic Liquid Contamination: Comparison to Water Flushing. Innovative subsurface remediation : field testing of physical, chemical and characterization technologies. ACS symposium series 725., 136-152.
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  Abstract: A pilot-scale field experiment was conducted to compare the remediation effectiveness of an enhanced-solubilization technique to that of water flushing for removal of multicomponent nonaqueous-phase organic liquid (NAPL) contaminants from a phreatic aquifer. This innovative remediation technique uses cyclodextrin, a sugar (glucose)-based molecule, to enhance the apparent aqueous solubility of organic contaminants. The cyclodextrin solution significantly increased not only the apparent solubility for several target contaminants, but also the rate of dissolution. As a result of these effects, the time required for cleanup of NAPL contamination at this field site may be greatly reduced by using cyclodextrin-enhanced flushing. For example, it was estimated that more than 70 000 pore volumes of water flushing would be required to remove the undecane mass that was removed in the 8-pore volume cyclodextrin flush, and for trichlorothene, which exhibited the smallest solubility enhancement, about 350 pore volumes of water flushing would be required.
• McCray, J. E., Bryan, K. D., Cain, R. B., Johnson, G. R., Blanford, W. J., & Brusseau, M. L. (1999). Field test of cyclodextrin for enhanced in-situ flushing of multiple-component immiscible organic liquid contamination: Comparison to water flushing. ACS Symposium Series, 725, 136-152.
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  Abstract: A pilot-scale field experiment was conducted to compare the remediation effectiveness of an enhanced-solubilization technique to that of water flushing for removal of multicomponent nonaqueous-phase organic liquid (NAPL) contaminants from a phreatic aquifer. This innovative remediation technique uses cyclodextrin, a sugar (glucose)-based molecule, to enhance the apparent aqueous solubility of organic contaminants. The cyclodextrin solution significantly increased not only the apparent solubility for several target contaminants, but also the rate of dissolution. As a result of these effects, the time required for cleanup of NAPL contamination at this field site may be greatly reduced by using cyclodextrin-enhanced flushing. For example, it was estimated that more than 70,000 pore volumes of water flushing would be required to remove the undecane mass that was removed in the 8-pore volume cyclodextrin flush, and for trichloroethene, which exhibited the smallest solubility enhancement, about 350 pore volumes of water flushing would be required.
• Mccray, J. E., & Brusseau, M. L. (1999). Cyclodextrin-enhanced in situ flushing of multiple-component immiscible organic liquid contamination at the field scale: Analysis of dissolution behavior. Environmental Science and Technology, 33(1), 89-95.
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  Abstract: There is great interest in the potential use of solubility-enhancing agents for subsurface remediation of non-aqueous-phase organic liquid (NAPL) contamination. Cyclodextrin was demonstrated to be effective for NAPL removal during a recent pilot-scale field study. The study provides an opportunity to investigate the mechanisms controlling mass transfer between a multicomponent NAPL and an enhanced-flushing agent solution at the field scale. A relationship is developed to describe enhanced dissolution of a multiple- component NAPL and is used to analyze the field data. While NAPL dissolution behavior was generally complex during the cyclodextrin flush, the initial peak and final effluent concentrations for most of the target contaminants were within a factor of 2 of the equilibrium values predicted using the ideal enhanced-dissolution theory. This suggests that the dissolution of the multicomponent NAPL during the cyclodextrin flush may be approximately treated, at least for practical purposes, as an ideal, equilibrium process. It appears that the dissolution theory successfully predicted the observed behavior for this system. Thus, it may be useful for assisting in the planning, design, and evaluation of other enhanced-flushing applications involving multicomponent NAPL.
• Nelson, N. T., Brusseau, M. L., Carlson, T. D., Costanza, M. S., Young, M. H., Johnson, G. R., & Wierenga, P. J. (1999). A gas-phase partitioning tracer method for the in situ measurement of soil-water content. Water Resources Research, 35(12), 3699-3707.
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  Abstract: The purpose of this paper is to describe a gas-phase partitioning tracer method for the in situ measurement of soil-water content and to illustrate the application and performance of the tracer method in well-defined systems. The method is based on the use of a tracer test with nonpartitioning and partitioning tracers introduced into the system in the gas phase. Partitioning tracers dissolve into the water, which retards their gas-phase transport relative to that of the nonpartitioning tracers. Retardation of the partitioning tracers is a function of the amount of water present. The method provides an integrated field-scale value that complements smaller-scale methods, such as neutron moderation, and regional-scale methods based on remote sensing. Experiments were conducted in the laboratory and in a large weighing lysimeter to test the performance of the gas-phase partitioning tracer method. Soil-water contents estimated from the tracer tests were reasonably close to values obtained using gravimetric and time domain reflectometry measurements, indicating the tracer method has the potential to provide accurate measurements of soil-water content at the field scale.
• Nelson, N. T., Oostrom, M., Wietsma, T. W., & Brusseau, M. L. (1999). Partitioning tracer method for the in situ measurement of DNAPL saturation: Influence of heterogeneity and sampling method. Environmental Science and Technology, 33(22), 4046-4053.
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  Abstract: The purpose of this work was to examine the effect of porous-media heterogeneity, nonuniform distribution of dense nonaqueous phase liquid (DNAPL), and sampling method on the performance of the partitioning tracer method for measuring DNAPL saturation in water-saturated subsurface systems. Experiments were conducted in an intermediate-scale flow cell that contained two discrete zones of trichloroethene (TCE) at residual saturation. One zone (zone 2) consisted of ~10% saturation formed in the same sand as used for the flow-cell matrix. The other zone (zone 1) consisted of ~10% saturation in a finer sand emplaced within the coarser matrix. Aqueous samples were collected using depth-specific sampling, using vertically integrated sampling, and at the extraction well. A dual-energy γ radiation system was used to measure TCE saturation before and after the tracer experiment, allowing the measurements obtained from the tracer experiment to be compared to a previously tested method. The saturations estimated using the data collected at point-sampling ports located downgradient of zones 1 and 2 were approximately 7% and 50% of the true values, respectively. The saturations estimated using the data obtained from the vertically integrated ports were 0% and 6% of the true values, respectively. Finally, the saturation estimated using the extraction-well data was 30% of the cell-wide averaged value. These results indicate that the presence of porous-media heterogeneity and a variable distribution of DNAPL saturation can lead to reduced accuracy of the partitioning tracer test. The reduced performance can be improved, in part, by using depth-specific sampling.
• Zhang, Z., & Brusseau, M. L. (1999). Nonideal transport of reactive solutes in heterogeneous porous media 5. Simulating regional-scale behavior of a trichloroethene plume during pump-and-treat remediation. Water Resources Research, 35(10), 2921-2935.
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  Abstract: 'Pump and treat' is widely used for containment and remediation of groundwater contaminant plumes. However, it is commonly observed that pump-and-treat systems begin to exhibit reduced efficiency at some point. A number of factors and processes may contribute to the reduced efficiency, among them being those associated with nonideal transport behavior, such as subsurface heterogeneity, nonlinear, rate-limited sorption/desorption, and rate-limited dissolution of immiscible liquid. We use numerical modeling to analyze the regional-scale (~49 km2) nonideal transport behavior of trichloroethene in a contaminated aquifer undergoing pump and treat remediation. The pump-and-treat system has been in operation for ~12 years, during which time the composite concentrations of trichloroethene in the treatment plant influent have decreased from >300 to ~100 μg L-1. However, as is typically observed elsewhere, the system is exhibiting extensive concentration tailing, wherein the concentrations have remained relatively constant at ~100 μg L-1 for the past 8 years. Various factors that may be contributing to this tailing phenomenon are evaluated using a three-dimensional solute transport model specifically developed for the site, which is located in Tucson, Arizona. The values for almost all of the input parameters of the model were obtained independently of the historic concentration data being simulated. The hydraulic conductivity field was generated using information obtained from borehole logs and pumping tests, the sorption and local-scale mass transfer parameters were obtained from laboratory experiments conducted with aquifer material collected from the site, and the initial immiscible-liquid saturations were based on the results of partitioning tracer tests conducted in a representative source zone at the site. On the basis of our analyses we conclude that while rate-limited desorption and large-scale spatial variability of hydraulic conductivity have significant impacts on trichloroethene transport, the dissolution of immiscible-liquid saturation associated with the source zones is most likely the primary cause of the extensive concentration tailing observed at the site. The impact of nonlinear sorption and local-scale mass transfer on trichloroethene removal appears to be insignificant.
• Bai, G., Brusseau, M. L., & Miller, R. M. (1998). Influence of cation type, ionic strength, and pH on solubilization and mobilization of residual hydrocarbon by a biosurfactant. Journal of Contaminant Hydrology, 30(3-4), 265-279.
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  Abstract: This study investigated the effect of cation type, ionic strength, and pH on the performance of an anionic monorhamnolipid biosurfactant for solubilization and removal of residual hexadecane from sand. Three common soil cations, Na+, Mg2+, and Ca2+, were used in these experiments and hexadecane was chosen to represent a nonaqueous phase liquid (NAPL) less dense than water. Results showed that hexadecane solubility in rhamnolipid solution was significantly increased by the addition of Na+ and Mg2+. Addition of up to 0.2 mM Ca2+ also increased hexadecane solubility. For Ca2+ concentrations greater than 0.2 mM there was little effect on hexadecane solubility due to competing effects of calcium-induced rhamnolipid precipitation and enhanced hexadecane solubilization. Efficiency of NAPL solubilization can be expressed in terms of molar solubilization ratios (MSR). The results showed that MSR values for hexadecane in rhamnolipid solutions increased 7.5-fold in the presence of 500 mM Na+, and 25-fold in the presence of 1 mM Mg2+. The presence of cations also reduced the interfacial tension between rhamnolipid solutions and hexadecane. For example, an increase in Na+ from 0 to 800 mM caused a decrease in interfacial tension from 2.2 to 0.89 dyn cm-1. Similarly, decreasing pH caused a reduction in interfacial tension. The lowest interfacial tension value observed in this study was 0.02 dyn cm-1 at pH 6 in the presence of 320 mM Na+. These conditions were also found to be optimal for removal of hexadecane residual from sand columns, with 58% of residual removed within three pore volumes. The removal of residual NAPL from the packed columns was primarily by mobilization, even though solubilization was significantly increased in the presence of Na+.
• Ball, W. P., Goltz, M. N., Roberts, P. V., Valocchi, A. J., & Brusseau, M. L. (1998). Comment on 'field-scale transport of nonpolar organic solutes in 3-D heterogeneous aquifers' [3]. Environmental Science and Technology, 32(17), 2654-2655.
• Blue, J. E., Brusseau, M. L., & Srivastava, R. (1998). Simulating tracer and resident contaminant transport to investigate the reduced efficiency of a pump-and-treat operation. IAHS-AISH Publication, 537-543.
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  Abstract: Influent trichloroethene (TCE) concentrations have levelled off at approximately 100 ppb during the 10 years of pump-and-treat conducted at a superfund site in Tucson, Arizona. A dual-well, forced-gradient tracer experiment was conducted to help evaluate the factors responsible for the extreme tailing. Tracer (bromide) breakthrough and resident TCE elution were monitored at an extraction well and at discrete levels of a centreline monitoring well. The vertical variability of hydraulic conductivity was analysed by layered numerical and analytical models. Parameters to be used in a TCE transport model were determined based upon laboratory experiments conducted using aquifer material from the site and from previous modelling results for flow and bromide transport. Some of the processes considered include rate-limited diffusion from low conductivity zones, rate-limited desorption, and rate-limited dissolution from immiscible liquid. These factors are important processes at many sites contaminated with organic pollutants.
• Boving, T., Wang, X., & Brusseau, M. L. (1998). Use of cyclodextrins for the remediation of solvent contaminated porous media. IAHS-AISH Publication, 437-440.
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  Abstract: Cyclodextrins are non-toxic, sugar-based substances that form complexes with many contaminants. Two different cyclodextrin varieties were investigated and it was shown that their presence in solution results in a significant increase of the apparent solubility of tetrachloroethylene (PCE) and trichloroethylene (TCE). By using a laboratory-scale air stripper, it was demonstrated that it is possible to reuse the cyclodextrin solution. Depending on the air flow rate, the necessary residence time of the cyclodextrin solution in the air stripper approaches that of cyclodextrin-free water.
• Brusseau, M. L. (1998). Non-ideal transport of reactive solutes in heterogeneous porous media: 3. Model testing and data analysis using calibration versus prediction. Journal of Hydrology, 209(1-4), 147-165.
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  Abstract: The transport of reactive solutes is often influenced by multiple factors and processes. Complex mathematical models accounting for these multiple factors and processes are required to simulate accurately the transport of reactive solutes. There are numerous concerns and constraints associated with the application of mathematical models to the transport of reactive solutes, especially for field-scale problems. The specific issue of using calibration (fitting a model to measured data) for model evaluation and data analysis was examined in this paper. Selected laboratory data, as well as the results of the well-known Borden natural-gradient field experiment were used as case studies to illustrate the potential pitfalls of using model calibration for the analysis of reactive solute transport. It is shown that erroneous parameter values can be obtained from calibration if all significant transport factors are not properly represented. Perhaps of greater significance, the (mis)use of calibration can lead to a mistaken belief that the model accurately represents the physical system and, hence, result in a misinterpretation of the factors controlling solute transport.
• Hu, M. Q., & Brusseau, M. L. (1998). Coupled effects of nonlinear, rate-limited sorption and biodegradation on transport of 2,4-dichlorophenoxyacetic acid in soil. Environmental Toxicology and Chemistry, 17(9), 1673-1680.
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  Abstract: The transport and fate of many contaminants in subsurface systems can be influenced by several coupled processes, such as nonlinear, rate-limited sorption and biodegradation. We investigated the transport in soil of a model organic compound, 2,4-dichlorophenoxyacetic acid (2,4-D), influenced by nonlinear, rate-limited sorption and biodegradation. Miscible displacement and batch sorption experiments were conducted using a wide range of solute concentrations to investigate the impact of concentration-dependent behavior on transport. The sorption isotherm was approximately linear at a low concentration, and nonlinear over the extended range of concentrations. Results from the transport experiments, with the fitted N values approaching I at low input concentrations, were consistent with the batch sorption study. Nonlinear sorption significantly influenced the position of the breakthrough curves because of concentration-dependent retardation. However, although both nonlinear and rate-limited sorption influenced the shape of the breakthrough curves, the impact of rate-limited sorption was greater. The effective travel time of 2,4-D transport is influenced by synergistic interactions between sorption and biodegradation. For example, the sequential rightward shift of the breakthrough curves with decreasing input concentration, due to nonlinear sorption of 2,4-D, is enhanced by biodegradation.
• Mccray, J. E., & Brusseau, M. L. (1998). Cyclodextrin-enhanced in situ flushing of multiple-component immiscible organic liquid contamination at the field scale: Mass removal effectiveness. Environmental Science and Technology, 32(9), 1285-1293.
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  Abstract: The feasibility of 'enhanced-solubility remidiation technologies, designed to enhance the removal of nonaqueous-phase organic liquids (NAPLs) from the subsurface, must be tested at the field scale. Herein are reported the results of an experiment designed to evaluate the effectiveness of a cyclodextrin (sugar) solution for enhanced-solubilization removal of a multicomponent NAPL from an aquifer. This effort is the first field test of this innovative technology, termed a 'complexing sugar flush' (CSF). The saturated zone within an enclosed cell was flushed with 8 pore volumes of a 10 wt % cyclodextrin solution. The cyclodextrin solution increased the aqueous concentrations of all the target contaminants to values from about 100 to more than 20 000 times the concentrations obtained during a water flush conducted immediately prior to the CSF. The degree of solubility enhancement was greater for the more-hydrophobic contaminants. Conversely, the relative mass removal was greater for the less-hydrophobic compounds due to their generally higher apparent solubilities, which effected a significant reduction in the initial mass during the relatively short experiment. The average reduction in soil-phase concentrations for the target contaminants was 41%. This mass-removal percentage corresponds well to the results of partitioning-tracer tests, which indicated a 44% reduction in the average NAPL saturation.
• Noordman, W. H., Wei, J. i., Brusseau, M. L., & Janssen, D. B. (1998). Effects of rhamnolipid biosurfactants on removal of phenanthrene from soil. Environmental Science and Technology, 32(12), 1806-1812.
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  Abstract: Solubilizing agents may enhance remediation of soils contaminated with hydrophobic organic contaminants by diminishing sorption of the contaminants or increasing desorption rates. The effectiveness of rhamnolipid biosurfactants to enhance the removal of sorbed contaminants from soil was determined using column studies. Soil columns were contaminated with phenanthrene and subsequently eluted with electrolyte solution or with electrolyte solution containing 500 mg/L rhamnolipid. For the four soils studied, removal of 50% of the phenanthrene from the soil columns was accomplished in a 2-5-fold shorter time period, and the time required for 90% removal was reduced up to 3.5-fold when elution was performed with the rhamnolipid-containing solution as compared to the treatment without rhamnolipid. The effect of rhamnolipid on the removal of phenanthrene was satisfactorily simulated using independently obtained parameters with a two- component advective-dispersive model accounting for micellar solubilization and admicellar sorption. A more detailed analysis of the system showed that desorption rates of phenanthrene in the presence of 500 mg/L rhamnolipid were higher than predicted on the basis of desorption rate constants of phenanthrene determined in the absence of rhamnolipid. It is concluded that rhamnolipid enhanced the removal of phenanthrene mainly by micellar solubilization and also by influencing sorption kinetics.
• Piatt, J. J., & Brusseau, M. L. (1998). Rate-limited sorption of hydrophobic organic compounds by soils with well-characterized organic matter. Environmental Science and Technology, 32(11), 1604-1608.
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  Abstract: This study is focused on the rate-limited sorption of homologous series of polycyclic aromatic hydrocarbons, alkylated benzenes, chlorinated benzenes, and chlorinated alkenes by two soils, one in which the organic matter is dominated by humic acid and the other by fulvic acid. The solutes sorbed more strongly to the humic-dominated soil than the fulvic-dominated soil. The first-order molecular connectivity index (1X(v)), a molecular solute descriptor, provided slightly better correlations with equilibrium sorption coefficients than did the octanol - water partition coefficient (K(ow)), an empirical solute descriptor. Thus, sorbate shape/structure may have a secondary influence on the overall magnitude of equilibrium sorption. However, sorbate shape/structure exhibited a significant influence on sorption kinetics. Distinct differences were observed in the correlations of mass-transfer coefficients to 1X(v) for the two soils. The differences were attributed to both sorbate shape/structure and the quantity (path length) and morphology of soil organic matter.
• Popovičová, J., & Brusseau, M. L. (1998). Contaminant mass transfer during gas-phase transport in unsaturated porous media. Water Resources Research, 34(1), 83-92.
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  Abstract: This study was conducted to investigate the relative effects of physical heterogeneity, gas-liquid mass transfer, and rate-limited sorption on the gas-phase transport of contaminants in idealized unsaturated homogeneous and heterogeneous porous media. The transport of methane in the unsaturated homogeneous porous medium was ideal, whereas that of trichloroethene and benzene was nonideal, governed by ratelimited diffusive mass transfer in immobile water and by rate-limited sorption/desorption. Transport of both methane and trichloroethene through the unsaturated heterogeneous porous medium was nonideal. Gas-phase mass transfer between unsaturated advective and nonadvective domains caused nonideal transport of methane. Trichloroethene nonideality was due to a combination of gas-phase mass transfer between advective and nonadvective domains, diffusion within immobile water, and rate-limited sorption/desorption. The transport of trichloroethene through the heterogeneous porous medium was predicted by use of a multiprocess mass transfer model, wherein all parameters were estimated independently.
• Wang, J., Marlowe, E. M., Miller-Maier, R. M., & Brusseau, M. L. (1998). Cyclodextrin-enhanced biodegradation of phenanthrene. Environmental Science and Technology, 32(13), 1907-1912.
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  Abstract: The effectiveness of in situ bioremediation in many systems may be constrained by low contaminant bioavailability due to limited aqueous solubility or a large magnitude of sorption. The objective of this research was to evaluate the effect of hydroxypropyl-β-cyclodextrin (HPCD) on phenanthrene solubilization and biodegradation. Results showed that analytical-grade HPCD can significantly increase the apparent solubility of phenanthrene. The increase in apparent solubility had a major impact on the biodegradation rate of phenanthrene. For example, in the presence of 105 mg L-1 HPCD, the substrate utilization rate increased from 0.17 mg h-1 to 0.93 mg h-1 while the apparent solubility was increased from 1.3 mg L-1 to 161.3 mg L-1. As a result, only 0.3% of the phenanthrene remained at the end of a 48 h incubation for the highest concentration of HPCD tested (105 mg L-1). In contrast, 45.2% of the phenanthrene remained in the absence of HPCD. Technical grade HPCD, which contains the biodegradable impurity propylene glycol, also increased the substrate utilization rate, although to a lesser extent than the analytical-grade HPCD. On the basis of these results, it appears that HPCD can significantly increase the bioavailability, and thereby enhance the biodegradation, of phenanthrene.
• Wang, X., & Brusseau, M. L. (1998). Effect of pyrophosphate on the dechlorination of tetrachloroethene by the Fenton reaction. Environmental Toxicology and Chemistry, 17(9), 1689-1694.
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  Abstract: The effectiveness of Fenton's reagent for the remediation of contaminated sandy soils is affected by the precipitation and sorption of Fe species in soil/water systems. We investigated the ability of pyrophosphate to maintain Fe in solution and thus enhance the dechlorination of tetrachloroethene (PCE) by the Fenton reaction. The results of the experiments showed that pyrophosphate could significantly increase the concentrations of Fe in aqueous solutions and enhance the dechlorination of PCE. The dechlorination rate of PCE in the presence of pyrophosphate was found to decrease with time, which was attributed to both the conversion of Fe(II) to Fe(III) and the decrease of aqueous Fe concentration. In comparison to organic chelating agents, pyrophosphate appeared to be more stable and thus catalyzed the dechlorination of PCE for a longer time. The extended dechlorination (>120 h) was attributed to the solubilization of Fe and the stabilization of H2O2 caused by the addition of pyrophosphate.
• Wei, J. i., & Brusseau, M. L. (1998). A general mathematical model for chemical-enhanced flushing of soil contaminated by organic compounds. Water Resources Research, 34(7), 1635-1648.
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  Abstract: The use of chemical agents to enhance the in situ removal of hydrophobic organic compounds (HOCs) from porous media is an emerging remediation technology. Whereas surfactants and cosolvents are the primary agents examined to date, others, such as natural organic matter and complexing agents, have also been examined for their ability to enhance the solubilization of HOCs. While the mode of action of each type of enhanced-solubilization agent may be different, they all induce similar responses. In this paper, a general mathematical model is developed to simulate the enhanced-solubilization process for various chemical agents, including cosolvents, surfactants, natural organic matter, and complexing agents. This model is developed using a master-equation approach that incorporates the solubilization mechanisms associated with each type of agent. A limited evaluation of the model is conducted by comparing simulations to the results of two laboratory experiments. A sensitivity analysis is performed to illustrate the influence of various factors on contaminant removal.
• Bai, G., Brusseau, M. L., & Miller, R. M. (1997). Influence of a rhamnolipid biosurfactant on the transport of bacteria through a sandy soil. Applied and Environmental Microbiology, 63(5), 1866-1873.
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  PMID: 16535601;PMCID: PMC1389156;Abstract: The objective of this study was to investigate the influence of an anionic rhamnolipid biosurfactant on the transport of bacterial cells through soil under saturated conditions. Three cell types with various hydrophobicities, i.e., Pseudomonas aeruginosa ATCC 9027, ATCC 27853, and ATCC 15442, were used in this study. In a series of experiments, columns packed with sterile sand were saturated with sterile artificial groundwater for 15 h, and then 3 pore volumes of 3H-labeled bacterial suspensions with various rhamnolipid concentrations was pumped through the column. This was followed by 4 pore volumes of the rhamnolipid solution alone. The measured bacterial cell breakthrough curves were optimized by using an advection- dispersion transport model incorporating two-domain reversible sorption (instantaneous and rate limited) and with two first-order sink terms for irreversible adsorption. The influence of the rhamnolipid on the surface charge densities of the bacteria and the porous medium was also investigated. The results show that the rhamnolipid enhanced the transport of all cell types tested. For example, the rhamnolipid increased the recovery of the most hydrophilic strain, ATCC 9027, from 22.5 to 56.3%. Similarly, the recovery of ATCC 27853 increased from 36.8 to 49.4%, and the recovery of ATCC 15442, the most hydrophobic strain, increased from 17.7 to 40.5% in the presence of the rhamnolipid. The negative surface charge density of the porous medium was increased, while the surface charge density of the bacteria was not changed in the presence of the rhamnolipid. The model results suggest that the rhamnolipid predominantly affected irreversible adsorption of cells.
• Blanford, W. J., Brusseau, M. L., & Klingel, E. J. (1997). Evaluation of an in-well aeration system to remediate a groundwater contamination site. ACS Division of Environmental Chemistry, Preprints, 37(1), 231-233.
• Brusseau, M. L., & Srivastava, R. (1997). Nonideal transport of reactive solutes in heterogeneous porous media 2. Quantitative analysis of the Borden natural-gradient field experiment. Journal of Contaminant Hydrology, 28(1-2), 115-155.
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  Abstract: Field experiments constitute an integral component of research on transport and fate of contaminants in the subsurface. One of the most well known of the few field experiments performed with reactive solutes is the natural-gradient experiment conducted at the Borden site during 1982 to 1984. A major finding of the experiment was that the transport of the reactive, organic compounds was nonideal. First, the velocities of the centers of mass of the plumes decreased with time, which was reflected in a temporal increase in effective retardation. Second, the longitudinal spreading observed for the organic solutes was about three times larger than that of the nonreactive tracers for an equivalent travel distance. Third, the breakthrough curves measured at selected monitoring points exhibited greater asymmetry compared to the nonreactive tracers. The cause(s) of the nonideal transport observed for the organic solutes has remained unexplained, despite a number of attempts. We have used a multi-scale, multi-factor mathematical model to successfully predict the displacement and spreading behavior of the tetrachloroethene and tetrachloromethane plumes. Based on our analyses, we conclude that a near-field trend of increasing sorption capacity was a primary cause of the deceleration of the centers of mass of the organic- solute plumes. The coupled effects of nonlinear sorption and enhanced spreading caused by spatially variable hydraulic conductivity and spatially variable sorption also influenced plume displacement. In addition, it is possible that the combination of spatially variable hydraulic conductivity and sorption contributed directly to plume deceleration. However, a magnitude of sorption variability larger than has been measured to date is required for this contribution to be significant. The combined spatial variability of hydraulic conductivity and sorption, and a potential negative cross correlation between them, appears to have been the major cause of the enhanced longitudinal spreading observed for the organic-solute plumes in comparison to the nonreactive-solute plumes. However, nonlinear sorption, the spatial trend of increasing sorption capacity, and rate-limited sorption/mass transfer also influenced spreading behavior. In total, it is evident that the transport of the organic compounds during the Borden natural-gradient field experiment was influenced by several interacting factors and coupled processes, and that accurate prediction of the observed behavior requires the use of a mathematical model that accounts for this complexity.
• Brusseau, M. L., Popovičová, J., & A., J. (1997). Characterizing gas-water interfacial and bulk-water partitioning for gas-phase transport of organic contaminants in unsaturated porous media. Environmental Science and Technology, 31(6), 1645-1649.
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  Abstract: This study was performed to investigate the impact of interfacial and bulk-water partitioning on the retention and retardation of gas-phase contaminants during transport in unsaturated porous media. Gas-flow experiments were conducted using columns packed with three types of sandy porous media. Moisture contents were 11.9%, 16.0%, and 9.4% for the columns packed with glass beads, silica sand, and aquifer material, respectively. Contaminant retardation was the sum of retention by the gas, aqueous, and solid phases and accumulation at the gas-water interface. The results indicated that 29-73% of total trichloroethene retardation was due to accumulation at the gas-water interface, depending on porous media type. Partitioning into the bulk water accounted for 12-30% of total trichloroethene retardation for the various systems. Given the potential significance of interfacial and bulk-water retention for contaminant transport and remediation, it is important to consider methods for characterizing these processes at the field scale. Gas-phase tracer experiments using a suite of phase-selective partitioning tracers in combination with nonreactive tracers, as presented herein, may be one viable approach. For example, CO2 was used successfully to measure the bulk-water content of the system, and heptane was used to determine the effective gas- water interfacial area.
• Brusseau, M. L., Qinhong, H. u., & Srivastava, R. (1997). Using flow interruption to identify factors causing nonideal contaminant transport. Journal of Contaminant Hydrology, 24(3-4), 205-219.
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  Abstract: The transport and fate of many contaminants in subsurface systems can be influenced by several rate-limited processes, such as rate-limited sorption, diffusional mass transfer, and transformation reactions. Identification of the controlling process in such systems is often difficult, and is confounded by the possible influence of additional factors such as nonlinear or hysteretic sorption. We present a relatively simple method, flow interruption, that can be used to discriminate between various sets of processes. The application of the method is illustrated with results obtained from experiments performed for selected systems. Specific process-pairs investigated include physical nonequilibrium vs. physical heterogeneity, rate-limited sorption vs. nonlinear sorption, and sorption vs. transformation reactions. The results show that, while both physical nonequilibrium and physical heterogeneity can cause enhanced spreading or dispersion, only the former causes a noticeable concentration perturbation upon imposition of flow interruption under typical conditions. In addition, while both rate-limited sorption and nonlinear sorption can cause breakthrough curves to exhibit tailing, only rate-limited sorption induces a concentration perturbation upon imposition of flow interruption. The information obtained from applying flow interruption can be used to assist in the planning of additional, process-specific experiments and to help identify appropriate mathematical models to be used for transport simulation.
• Brusseau, M. L., Wang, X., & Wang, W. (1997). Simultaneous elution of heavy metals and organic compounds from soil by cyclodextrin. Environmental Science and Technology, 31(4), 1087-1092.
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  Abstract: A major factor complicating the cleanup of many sites is the co- occurrence of organic compounds and heavy metals, so-called mixed wastes. We investigated the ability of cyclodextrin to simultaneously remove heavy metals and low-polarity organic compounds from contaminated soil. The results of the experiments showed that cyclodextrin could greatly enhance the simultaneous desorption and elution of the model organic compound (phenanthrene) and the model heavy metal (cadmium) from the three soils examined. The soils consisted of a sandy aquifer material containing minimal organic carbon and clay, a soil with a relatively high clay content (10.2%), and a soil with a relatively high organic carbon content (1.4%). Elution of phenanthrene that was in contact with soil for 38 days exhibited greater tailing than the unaged phenanthrene when water was the flushing solution, indicating greater resistance to desorption and removal. Conversely, the elution curves for the aged and unaged phenanthrene were essentially identical for the cyclodextrin solution. Aging appeared to have no significant impact on cadmium elution behavior for either solution. In a majority of cases, the measured enhancedremoval factors for the contaminant elution curves were similar to the values expected based on complexation/solubilization theory.
• Guiyun, B., Brusseau, M. L., & Miller, R. M. (1997). Biosurfactant-enhanced removal of residual hydrocarbon from soil. Journal of Contaminant Hydrology, 25(1-2), 157-170.
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  Abstract: An anionic monorhamnolipid biosurfactant produced by Pseudomonas aeruginosa was investigated for its potential to remove residual hexadecane from sand columns. In a series of column experiments, residual hexadecane saturation was established by pumping 14C-hexadecane into water-saturated sand columns and then flushing with water at a velocity of 25 cm h-1. Monorhamnolipid solutions of varying concentration were then applied to the columns at a velocity of 15 cm h-1 to remove the residual hexadecane. Of the rhamnolipid concentrations tested, which ranged from 40 to 1500 mg l-1, the optimal concentration for residual removal was 500 mg l-1, approximately ten times the critical micelle concentration (cmc). Approximately 84% of the residual was removed from the column packed with 20/30 mesh sand, and 22% was removed from the 40/50 mesh column. The primary mechanism for residual removal was mobilization (displacement and dispersion), whereas solubilization was found to be insignificant. The performance of monorhamnolipid was compared with that of two synthetic surfactant solutions on a mass basis (500 mg l-1) for the 40/50 mesh sand. Sodium dodecyl sulfate (0.2 x cmc), and polyoxyethylene (20) sorbitan monooleate (38 x cmc), removed 0% and 6.1% of the residual saturation, respectively.
• Gupta, K., Qinhong, H. u., & Brusseau, M. L. (1997). Advanced characterization of a superfiind site: Effect of core-scale heterogeneity on trichloroethene transport. ACS Division of Environmental Chemistry, Preprints, 37(1), 257-259.
• Luthy, R. G., Aiken, G. R., Brusseau, M. L., Cunningham, S. D., Gschwend, P. M., Pignatello, J. J., Reinhard, M., Traina, S. J., Weber Jr., W. J., & Westall, J. C. (1997). Sequestration of hydrophobic organic contaminants by geosorbents. Environmental Science and Technology, 31(12), 3341-3347.
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  Abstract: The chemical interactions of hydrophobic organic contaminants (HOCs) with soils and sediments (geosorbents) may result in strong binding and slow subsequent release rates that significantly affect remediation rates and endpoints. The underlying physical and chemical phenomena potentially responsible for this apparent sequestration of HOCs by geosorbents are not well understood. This challenges our concepts for assessing exposure and toxicity and for setting environmental quality criteria. Currently there are no direct observational data revealing the molecular-scale locations in which nonpolar organic compounds accumulate when associated with natural soils or sediments. Hence macroscopic observations are used to make inferences about sorption mechanisms and the chemical factors affecting the sequestration of HOCa by geosorbents. Recent observations suggest that HOC interactions with geosorbents comprise different inorganic and organic surfaces and matrices, and distinctions may be drawn along these lines, particularly with regard to the roles of inorganic micropores, natural sorbent organic matter components, combustion residue particulate carbon, and spilled organic liquids. Certain manipulations of sorbates or sorbent media may help reveal sorption mechanisms, but mixed sorption phenomena complicate the interpretation of macroscopic data regarding diffusion of HOC into and out of different matrices and the hysteric sorption and aging effects common y observed for geosorbents. Analytical characterizations at the microscale, and mechanistic models derived therefrom, are needed to advance scientific knowledge of HOC sequestration, release, and environmental risk.
• Nelson, N., & Brusseau, M. L. (1997). Advanced characterization of a superfund site: Tracer tests and contaminant monitoring. ACS Division of Environmental Chemistry, Preprints, 37(1), 255-257.
• Popovičová, J., & Brusseau, M. L. (1997). Dispersion and transport of gas-phase contaminants in dry porous media: Effect of heterogeneity and gas velocity. Journal of Contaminant Hydrology, 28(1-2), 157-169.
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  Abstract: The purpose of these experiments was to study the effects of physical heterogeneity and velocity on transport of gas-phase contaminants in dry porous media. Experiments were conducted at gas velocities ranging from 6 to 200 cm min-1 to examine the contributions of longitudinal molecular diffusion, hydrodynamic dispersion, and rate-limited diffusive mass transfer to solute spreading. Methane was used as a nonreactive tracer, and trichloroethene, benzene and toluene were used as reactive tracers. Total dispersion of methane during transport through a homogeneous porous medium was the sum of longitudinal molecular diffusion and hydrodynamic dispersion. The latter was the major process contributing to total dispersion at gas velocities greater than 40 cm min-1. The contribution of longitudinal molecular diffusion was negligible at gas velocities greater than 150 cm min-1. Transport of tracers in the heterogeneous (macroporous) medium exhibited preferential flow and tailing at gas velocities greater than about 100 cm min-1 as a result of rate-limited mass transfer between macropore and micropore domains. The spreading associated with rate-limited mass transfer between macropore and micropore domains was the main contributor to total dispersion at gas velocities greater than 120 cm min-1. The transport of the reactive tracers was successfully predicted using data obtained for the nonreactive tracer.
• Wang, W., Brusseau, M. L., & Artiola, J. F. (1997). The use of calcium to facilitate desorption and removal of cadmium and nickel in subsurface soils. Journal of Contaminant Hydrology, 25(3-4), 325-336.
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  Abstract: The transport and elution behavior of Cd and Ni in the presence of Ca in subsurface soils was investigated using hatch and miscible-displacement experiments. The adsorption of Cd and Ni by the soils was dramatically decreased and their transport through the soils was significantly enhanced in the presence of Ca. These effects were attributed to the competition between Ca and these metals for exchange sites on the soil surfaces. The volume of CaCl2 solution required to remove a certain % of Cd decreased with increasing concentration of CaCl2. However, the concentration of CaCl2 used to flush the soil did not significantly affect the final % of Cd removed, which was 90%. The position of the Cd elution peak varied with Ca concentration due to the nonlinear sorption behavior of Ca.
• Brusseau, M. L. (1996). Evaluation of simple methods for estimating contaminant removal by flushing. Ground Water, 34(1), 19-22.
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  Abstract: The purpose of this work was to briefly outline and evaluate simple methods used for estimating the volume of water and the time required to remove contaminants from the surface by flushing (e.g., "pump-and-treat," "soil washing"). The methods are based on three general approaches to treating flow and transport: perfectly mixed flow, hydraulic, and advective-dispersive. Data obtained from a small field experiment designed to evaluate aquifer flushing was used to illustrate the performance of the estimation methods. The methods based on the hydraulic and ideal advective-dispersive transport approaches will generally provide estimates that underpredict the actual time. The magnitude of the underprediction will depend, in part, on the degree of nonideal behavior influencing contaminant removal (e.g., heterogeneity, rate-limited mass transfer) and on the ratio of target to initial contaminant concentration. The perfectly mixed flow reactor approach, because of its asymptotic removal curve, may be useful in providing rough approximations of required pore volumes and times. However, it cannot be overemphasized that all estimation technique are prone to failure as long as the conceptual models upon which they are based do not accurately represent field-scale contaminant transport.
• Linlin, X. u., & Brusseau, M. L. (1996). Semianalytical solution for solute transport in porous media with multiple spatially variable reaction processes. Water Resources Research, 32(7), 1985-1991.
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  Abstract: A small-perturbation semianalytical solution is derived for solute transport in porous media with multiple spatially variable reaction processes. Specific reactions of interest include reversible sorption, reversible mass transfer, and irreversible transformation (such as radioactive decay, hydrolysis reactions with fixed pH, and biodegradation). Laplace transform is employed to eliminate the time derivatives in the linear transport equations, and the transformed equations are solved analytically. The transient solution is ultimately obtained by use of an efficient quotient-difference inversion algorithm. Results indicate that spatial variation of transformation constants for the solution phase and the sorbed- phases decreases the global rate of mass loss and enhances solute transport. If the sorbed-phase transformation constant is spatially uniform but not zero, a similar effect is observed when there is spatial variation of the equilibrium sorption coefficient. The global rate of mass loss and apparent retardation are decreased when the spatial variability of the sorbed-phase transformation constant is positively correlated with the spatial variability of the equilibrium sorption coefficient and increased for a negative correlation.
• Nelson, N. T., & Brusseau, M. L. (1996). Field study of the partitioning tracer method for detection of dense nonaqueous phase liquid in a trichloroethene-contaminated aquifer. Environmental Science and Technology, 30(9), 2859-2863.
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  Abstract: Dense nonaqueous phase liquids (DNAPL) occur in the subsurface at numerous contaminated sites and can act as long-term sources of both vapor-phase and groundwater contamination. A new method of site characterization for DNAPL has been developed which involves the use of partitioning tracers. An experiment has been conducted to test the use of these tracers as detectors of potential DNAPL saturation in a trichloroethene-contaminated aquifer at a Superfund site.
• Qinhong, H. u., & Brusseau, M. L. (1996). Transport of rate-limited sorbing solutes in an aggregated porous medium: A multiprocess non-ideality approach. Journal of Contaminant Hydrology, 24(1), 53-73.
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  Abstract: The purpose of this work is to investigate the transport of rate-limited sorbing solutes in a saturated, aggregated porous medium. Data obtained from miscible displacement experiments are used to examine the transport of solutes constrained by rate-limited sorption and mass transfer, to examine the synergistic effects of two non-ideality factors, and to test the capability of a multiprocess non-equilibrium (MPNE) model to simulate transport. The input parameters were obtained independently, allowing the model to be used in a predictive mode. The independent predictions obtained with the MPNE model provided very good descriptions of the experimental data for several organic solutes with different structures. The effects of multiple non-ideality factors controlling solute transport were explored, and flow interruption experiments provided additional evidence regarding the synergistic effects of rate-limited sorption and rate-limited mass transfer, Our analyses have shown quantitatively that both mass distribution and characteristic reaction time are important factors influencing transport. Solute characteristics controlled the degree to which each factor influenced transport behavior for a given porous medium. The velocity dependency of the mass-transfer and desorption rate coefficients and the resultant impact on solute transport were also examined.
• Srivastava, R., & Brusseau, M. L. (1996). Nonideal transport of reactive solutes in heterogeneous porous media: 1. Numerical model development and moments analysis. Journal of Contaminant Hydrology, 24(2), 117-143.
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  Abstract: The transport of reactive solutes at the field scale is characteristically nonideal, and this nonideality is often caused by more than one factor. In these cases, mathematical models that explicitly account for multiple factors are necessary for proper simulation of transport and for accurate analysis of causative factors. The purpose of this paper is to present a mathematical model for simulating the transport of reactive solute in heterogeneous porous media. We have taken a multi-scale, multi-factor approach that explicitly accounts for such factors as hydraulic-conductivity variability, structured porous media, rate-limited diffusive mass transfer, and nonlinear, rate-limited, spatially variable sorption. The influence of these factors on the displacement and spreading of solute plumes and on mass flux is illustrated with a series of two-dimensional (vertical) simulations. It is shown that rate-limited sorption/mass transfer and nonlinear sorption can significantly influence the first, second, and third spatial moments, whereas hydraulic-conductivity variability significantly influences only the second spatial moment. Plume skewness is especially sensitive to the specific factor controlling nonideal transport. For example, both rate-limited sorption/mass transfer and nonlinear sorption can create negatively skewed plumes during early stages of transport. However, the plume influenced by rate-limited sorption/mass transfer tends toward symmetry as global residence time increases. Conversely, the plume influenced by nonlinear sorption tends toward a constant degree of asymmetry as the spreading forces balance the concentration-dependent retardation behavior associated with nonlinear sorption. Furthermore, the results illustrate that unique behavior can result from the coupling of multiple processes. For example, when influenced by coupled heterogeneity and nonlinear sorption, the shape of a plume may change from positive to negative skewness during the course of transport.
• Brusseau, M. L. (1995). The effect of nonlinear sorption on transformation of contaminants during transport in porous media. Journal of Contaminant Hydrology, 17(4), 277-291.
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  Abstract: The transport of contaminants through porous media is influenced by several processes, two of the most important being sorption and transformation. Several mathematical models have been developed to investigate the effects of sorption and transformation on contaminant transport. Almost all of these models are based on the assumption of linear sorption. However, it is well known that sorption of reactive contaminants is often nonlinear. A mathematical model that describes the transport of solute undergoing nonlinear, rate-limited sorption and first-order transformation is used to investigate the effect of coupled transformation and non-linear sorption on contaminant transport. Results of the analyses show that a model based on linear sorption cannot provide an accurate simulation of the transformation and transport of nonlinearly sorbing solutes when n is less than ∼0.9. In addition, the relative impact of non-linear sorption on solute transport is mediated by the magnitude of transformation. The nondimensional time required for a specified fraction of solute mass to be transformed during transport is influenced by nonlinear sorption. These examples illustrate the intriguing effects that coupled processes can have on contaminant transport and which may be important for many contaminants of interest. © 1995.
• Popovicova, J., & Brusseau, M. L. (1995). Transport of gas-phase contaminants through structured unsaturated porous media. Groundwater quality: remediation and protection. Proc. conference, Prague, 1995, 133-138.
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  Abstract: Soil venting is a widely used technology for removal of volatile organic compounds from the unsaturated zone. However its efficiency and length of operation is subject to many constraints. The presence of an heterogeneous porous medium is one potential cause of reduced efficiency. A laboratory column study to investigate effect of diffusion between macropore and micropore domains on tracer transport was performed. Dry glass beads and an artificial macropore were used to simulate a structured porous medium. The contribution of hydrodynamic dispersion, axial diffusion, and diffusion between macropore and micropore domains to total tracer dispersion was quantified. Diffusion between macropore and micropore domains was the major contributing process to gas dispersion at gas velocities >120 cm min-1. -from Authors
• Qinhong, H. u., & Brusseau, M. L. (1995). Dispersive-diffusive transport of non-sorbed solute in multicomponent solutions. Journal of Contaminant Hydrology, 19(4), 261-267.
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  Abstract: The composition of fuels, mixed-solvent wastes and other contaminants that find their way into the subsurface are frequently chemically complex. The dispersion and diffusion characteristics of multicomponent solutions in soil have rarely been compared to equivalent single-solute systems. The purpose of this work was to examine the diffusive and dispersive transport of single- and multi-component solutions in homogeneous porous media. The miscible displacement technique was used to investigate the transport behavior of 14C-labelled 2,4-dichlorophenoxyacetic acid (2,4-D) in two materials for which sorption of 2,4-D was minimal. Comparison of breakthrough curves collected for 2,4-D in single- and multi-component solutions shows that there is little, if any, difference in transport behavior over a wide range of pore-water velocities (70, 7, 0.66 and 0.06 cm h-1). Thus, dispersivities measured with a non-sorbing single-solute solution should be applicable to multicomponent systems. © 1995.
• Qinhong, H. u., & Brusseau, M. L. (1995). Effect of solute size on transport in structured porous media. Water Resources Research, 31(7), 1637-1646.
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  Abstract: Miscible displacement experiments were performed with tracers of different sizes in aggregated, stratified, and macroporous media. The breakthrough curves exhibited both early breakthrough and tailing, indicative of nonideal transport in these structured media. Comparison of breakthrough curves revealed that the extent of nonideality (eg tailing) was HPCD > PFBA, 2,4-D > 3H2O. Experiments performed with tracers of different size are useful for characterizing the nature of the porous medium through which transport is occurring. -from Authors
• Qinhong, H. u., Wang, X., & Brusseau, M. L. (1995). Quantitative structure-activity relationships for evaluating the influence of sorbate structure on sorption of organic compounds by soil. Environmental Toxicology and Chemistry, 14(7), 1133-1140.
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  Abstract: The purpose of this work was to investigate the effect of sorbate structure, by using the quantitative structure-activity relationship (QSAR) approach, on sorption of organic compounds by two soils with different amounts of organic matter. Miscible displacement experiments were performed with several organic contaminants representing six classes of nonpolar, nonionizable organic chemicals, including chlorinated aliphatics, chlorobenzenes, polycyclic aromatic hydrocarbons (PAHs), n-alkylbenzenes, methylated benzenes, and polychlorinated biphenyls (PCBs). The breakthrough curves were analyzed by using a bicontinuum model wherein sorption is assumed to be instantaneous for a fraction of the sorbent and rate limited for the remainder. The QSAR approach was used to investigate the dependency of both equilibrium and nonequilibrium sorption coefficients on topological descriptors representing structural properties of the solutes. For both equilibrium and nonequilibrium parameters, the first-order valence molecular connectivity (1xv) was found to be the best topological descriptor. Most of the rate-limited sorption behavior could be explained by accounting for the size and structure of the solute molecule, as indicated by the good correlation between the rate coefficient and 1xv. This supports the contention that rate-limited sorption in these systems is controlled by a physical diffusion mechanism, consistent with the polymer diffusion model. Based on this model, the calculated diffusion-length ratios for the Borden and Mt. Lemmon soils, which have a large difference in organic-matter contents, compare favorably to the values determined from the measured rate data. © 1995.
• Srivastava, R., & Brusseau, M. L. (1995). Darcy velocity computations in the finite element method for multidimensional randomly heterogeneous porous media. Advances in Water Resources, 18(4), 191-201.
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  Abstract: For numerical modeling of transport of contaminants through porous media, an accurate determination of the velocity field is a prerequisite. Some previous schemes of obtaining the Darcian velocity field through numerical solution of the flow equation result in a physically inconsistent velocity distribution in a heterogeneous medium. A scheme that is consistent with the physics of velocity variation near material interfaces is examined and compared with previous schemes. Numerical simulations are used to demonstrate the capability and accuracy of the proposed scheme for randomly heterogeneous porous media. © 1995.
• Wang, X., & Brusseau, M. L. (1995). Cyclopentanol-enhanced solubilization of polycyclic aromatic hydrocarbons by cyclodextrins. Environmental Science and Technology, 29(9), 2346-2351.
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  Abstract: The effect of cyclopentanol on the solubilization of six polycyclic aromatic hydrocarbons (PAHs) by β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) is reported in this paper. The addition of 0.1% v/v cyclopentanol significantly enhances the solubilization power of β-CD for pyrene, acenaphthene, phenanthrene, and fluoranthene, which form 1:2 complexes with β-CD. However, the solubilization of acenaphthene and phenanthrene by β-CD in the presence of cyclopentanol decreases at higher β-CD concentrations following an initial increase. This phenomenon is attributed to the cyclopentanol-induced formation of insoluble β-CD aggregates. In contrast, cyclopentonal produces no pronounced effect and a marked decrease in the solubilization power of β-CD for naphthalene and anthracene, respectively. These two compounds form 1:1 complexes with β-CD. The solubilization of all six PAHs by γ-CD is significantly enhanced by 1% v/v cyclopentanol. This result indicates that the addition of cyclopentanol increases the 'hydrophobicity' of the γ-CD cavity and increases the solubilization power of γ-CD without inducing structure-dependent selectivity. On the basis of linearity and nonlinearity observed in the solubilization curves of the six PAHs in the presence of cyclopentanol, it is suggested that naphthalene, anthracene, acenaphthene, and phenanthrene form 1:1 complexes with γ-CD while fluoranthene and pyrene form both 1:1 and 2:2 complexes.
• Wang, X., & Brusseau, M. L. (1995). Simultaneous complexation of organic compounds and heavy metals by a modified cyclodextrin. Environmental Science and Technology, 29(10), 2632-2635.
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  Abstract: The cleanup of contaminated soil and groundwater at hazardous waste sites has become a major focus of research and policy debate. A major factor complicating the cleanup of many sites is the cooccurrence of organic compounds and heavy metals, the so-called mixed wastes. We investigated the ability of a modified cyclodextrin to simultaneously complex low-polarity organic compounds and heavy metals. The results of the experiments showed that carboxymethyl-β-cyclodextrin could simultaneously increase the apparent aqueous solubilities of the selected organic compounds (anthracene, trichlorobenzene, biphenyl, and DDT) and complex with Cd2+. This complexation was not significantly affected by changes in pH or by the presence of relatively high concentrations of Ca2+. It is possible that this reagent can be used successfully to remediate hazardous waste sites contaminated by mixed wastes.
• Xu, L., & Brusseau, M. L. (1995). A combined Laplace transform and streamline upwind approach for nonideal transport of solutes in porous media. Water Resources Research, 31(10), 2483-2489.
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  Abstract: A new numerical method for nonideal transport of solutes in porous media is developed by first using the Laplace transform to eliminate the time dependency and then the streamline upwind scheme to solve the spatial equations. The transient solution is ultimately recovered by an efficient quotient difference inversion algorithm. Both one-dimensional and two-dimensional numerical examples are used to illustrate applications of this technique. -from Authors
• Brusseau, M. L. (1994). Transport of reactive contaminants in heterogeneous porous media. Reviews of Geophysics, 32(3), 285-313.
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  Abstract: The potential for human activities to adversely affect the environment has become of increasing concern during the past two decades. Concomitantly, the transport and fate of contaminants in subsurface systems has become one of the major research areas in the environmental, hydrological, and Earth sciences. An understanding of how contaminants move in the subsurface is needed to evaluate the probability of contaminants associated with a chemical spill reaching an aquifer and contaminating groundwater. This knowledge is also required to develop and evaluate methods for cleaning up contaminated soils and aquifers. Just as importantly, knowledge of contaminant transport and fate is necessary to design "pollution prevention" strategies. A tremendous body of literature on contaminant transport has been generated in response to these needs. This literature consists primarily of results obtained by theoretical, experimental, and mathematical modeling based investigations and, to a much lesser extent, field experiments. This paper consists of a brief review of some of the major aspects associated with the transport of reactive contaminants in heterogeneous subsurface environments. It begins with a review of basic concepts related to contaminant transport, followed by a discussion of the results obtained from some of the few well-controlled field experiments designed to investigate transport of reactive contaminants in the subsurface. Some of the major factors controlling contaminant transport will then be discussed, followed by a review of conceptual and mathematical approaches used to represent those factors in mathematical models. A brief overview of future needs and opportunities in contaminant transport will close the discussion.
• Brusseau, M. L., Gerstl, Z., Augustijn, D., & Rao, P. S. (1994). Simulating solute transport in an aggregated soil with the dual-porosity model: Measured and optimized parameter values. Journal of Hydrology, 163(1-2), 187-193.
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  Abstract: The capability of the first-order, dual-porosity model, which explicitly accounts for non-ideal transport caused by the presence of `immobile' water, to predict the non-ideal transport of non-sorbing solute in a constructed aggregated soil has been investigated. Miscible-displacement experiments performed with a well-characterized aggregated soil and a non-reactive tracer (pentafluorobenzoate) served as the source of the data. Values for the input parameters associated with physical non-equilibrium were determined independently and compared with values obtained by curve fitting of the experimental measurements. The calculated and optimized values compared well, suggesting that the non-equilibrium parameters represent actual physical phenomena.
• Brusseau, M. L., Wang, X., & Hu, Q. (1994). Enhanced transport of low-polarity organic compounds through soil by cyclodextrin. Environmental Science and Technology, 28(5), 952-956.
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  Abstract: The removal of low-polarity organic compounds from soils and aquifers by water flushing is often constrained by sorption interactions. There is great interest in developing systems that can enhance the transport of organic compounds through porous media, thus facilitating remediation. We investigated the potential of hydroxypropyl-β-cyclodextrin (HPCD), a microbially produced compound, to reduce the sorption and to enhance the transport of several low-polarity organic compounds. The results show that cyclodextrin does not interact with the two porous media used in the study. As a result, there is no retardation of cyclodextrin during transport. The retardation of compounds such as anthracene, pyrene, and trichlorobiphenyl was significantly (orders of magnitude) reduced in the presence of cyclodextrin. The enhancement effect of the cyclodextrin was predictable with a simple equation based on three-phase partitioning. The nonreactive nature of cyclodextrin combined with its large affinity for low-polarity organic compounds makes cyclodextrin a possible candidate for use in in-situ remediation efforts.
• Qinhong, H., & Brusseau, M. L. (1994). The effect of solute size on diffusive-dispersive transport in porous media. Journal of Hydrology, 158(3-4), 305-317.
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  Abstract: The purpose of this work was to investigate the effect of solute size on diffusive-dispersive transport in porous media. Miscible displacement experiments were performed with tracers of various sizes (i.e. tritiated water (3H2O), pentafluorobenzoate (PFBA), and 2,4-dichlorophenoxyacetic acid (2,4-D)) and a homogeneous, nonreactive sand for pore-water velocities varying by three orders of magnitude (70, 7, 0.66, and 0.06 cm h-1). Hydrodynamic dispersion is the predominant source of dispersion for higher pore-water velocities (exceeding 1 cm h-1), and dispersivity is, therefore, essentially independent of solute size. In this case, the practice of using a small-sized tracer, such as 3H2O, to characterize the dispersive properties of a soil is valid. The contribution of axial diffusion becomes significant at pore-water velocities lower than 0.1 cm h-1. At a given velocity below this value, the contribution of axial diffusion is larger for 3H2O, with its larger coefficient of molecular diffusion, than it is for PFBA and 2,4-D. The apparent dispersivities are, therefore, a function of solute size. The use of a tracer-derived dispersivity for solutes of different sizes would not be valid in this case. For systems where diffusion is important, compounds such as PFBA are the preferred tracers for representing advective-dispersive transport of many organic contaminants of interest.
• Tan, H., Champion, J. T., Artiola, J. F., Brusseau, M. L., & Miller, R. M. (1994). Complexation of cadmium by a rhamnolipid biosurfactant. Environmental Science and Technology, 28(13), 2402-2406.
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  Abstract: The potential of microbially-produced surfactants (biosurfactants) to complex heavy metals was investigated in this study. Batch solution studies using a model metal, cadmium, and an anionic monorhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 showed that complexation of the metal and biosurfactant was rapid and stable and achieved high reductions in the free Cd2+ concentration. For example 92% of Cd2+ (0.72 mM) was complexed by 7.3 mM rhamnolipid, and 97% of Cd2+ (0.36 mM) was complexed by 3.9 mM rhamnolipid. Under the experimental conditions used, the maximum complexation capacity of the rhamnolipid was 0.2 Cd2+/rhamnolipid on a molar basis. The calculated cadmium-rhamnolipid stability constant (log K = - 2.47) was higher than those reported for cadmium-sediment and cadmium-humic acid systems. The calculated cadmium-rhamnolipid equilibrium partition coefficient (log K(p) = 4.89) was similar to values reported for sorption of organic contaminants by dissolved organic matter. Quantitative separation and recovery of the rhamnolipid from the rhamnolipid-Cd2+ complexes were achieved by acid precipitation of the rhamnolipid followed by centrifugation.
• Brusseau, M. L. (1993). The influence of solute size, pore water velocity, and intraparticle porosity on solute dispersion and transport in soil. Water Resources Research, 29(4), 1071-1080.
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  Abstract: Intraparticle porosities of three sandy media were shown to constitute negligible fractions of the total porosities. As a result, intraparticle diffusion did not contribute to dispersive flux. The contribution of intraparticle diffusion, as well as film diffusion, to solute dispersion in fine-grained media having small intraparticle porosities will be negligible for most conditions. In addition, the importance of axial diffusion decreases as pore water velocity increases. Hydrodynamic dispersion is the predominant source of dispersion under these conditions, and, as such, dispersivity is essentially independent of solute size. Dispersivities determined with a tracer may therefore be used to represent the disersivity of other, dissimilar-sized solutes. Under these conditions, the practice of using a nonreactive tracer such as 3H2O to characterize the dispersive properties of a soil-column is valid. Solute dispersion in an aggregated soil was shown to be caused by a combination of hydrodynamic dispersion, film diffusion, and intraparticle diffusion. -from Author
• Brusseau, M. L. (1993). Using QSAR to evaluate phenomenological models for sorption of organic compounds by soil. Environmental Toxicology and Chemistry, 12(10), 1835-1846.
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  Abstract: The functional dependencies of equilibrium and nonequilibrium sorption parameters on solute molecular descriptors were analyzed for 29 organic compounds and two soils. Similar correlation patterns were obtained with all three evaluated size/shape descriptors (molecular surface area, van der Waals volume, molecular connectivity). The functional dependencies of equilibrium distribution coefficients on the solute molecular descriptors were analyzed for three systems used as phenomenological models of sorption by soil (octanol, reversed-phase HPLC packing material [RPLC], polymer). The correlation patterns exhibited by the three models were compared to those reported for the soil systems. The correlation patterns exhibited by the soil data were similar to the patterns exhibited by the polymer systems and dissimilar to those exhibited by the octanol and RPLC systems. In addition, the correlation pattern between the sorption rate coefficient and molecular connectivity was similar to that between polymer-diffusion coefficients and molecular connectivity. Hence, it appears that the polymer analog may be the most appropriate of the three models for representing both equilibrium and nonequilibrium sorption by soil. Based on these results, the polymer analog is suggested as the phenomenological model of choice for investigating and evaluating the sorption dynamics of low-polarity organic compounds in soil systems. © 1993.
• Brusseau, M. L., & Zachara, J. M. (1993). Transport of Co²⁺ in a physically and chemically heterogeneous porous medium. Environmental Science and Technology, 27(9), 1937-1939.
• Linn, D. M., Carski, T. H., Brusseau, M. L., & Chang, F. -. (1993). Sorption and degradation of pesticides and organic chemicals in soil. Proceedings of a symposium, Denver, October 1991. Sorption and degradation of pesticides and organic chemicals in soil. Proceedings of a symposium, Denver, October 1991.
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  Abstract: The 14 individually authored contributions bring together current thinking on: coupling biodegradation of organic chemicals to sorption and transport in soils and aquifers; degradation of atrazine and metolachlor in subsoils from an Atlantic Coastal Plain watershed; biodegradation of atrazine and alachlor in subsurface sediments; diazinon degradation and dissipation in the root zone; effect of soil depth on carbofuran and aldicarb degradation; effect of sorption-desorption and diffusion processes on the kinetics of biodegradation of organic chemicals; miscible dispacement and theoretical techniques for simultaneous study of pesticide sorption and degradation during transport; effect of sorption on the degradation of aromatic acids and bases; reductive dechlorination of hexachlorobenzene in wetland soils; bioavailability and bioactivity of sorbed organic chemicals; influence of contaminant ageing and soil organic carbon content on the bioavailability of sorbed napthalene to bacteria; utility of sorption and degradation parameters from the literature for site-specific pesticide impact assessments; integradation between physiochemical processes and microbial ecology in the enhanced biodegradation of soil pesticides; and enhanced biodegradation of the nematicide fenamiphos. -J.W.Cooper
• Wang, X., & Brusseau, M. L. (1993). Solubilization of some low-polarity organic compounds by hydroxypropyl- β-cyclodextrin. Environmental Science and Technology, 27(13), 2821-2825.
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  Abstract: Hydroxypropyl-β-cyclodextrin (HPCD), a microbially produced compound, was investigated for its potential to increase the apparent aqueous solubilities of low-polarity organic compounds. The results show that the apparent solubilities of trichloroethene, chlorobenzene, naphthalene, anthracene, and p,p'-DDT were significantly increased in HPCD solutions. The relative aqueous-phase concentrations (S(t)/S(o)) of the compounds increased linearly with increasing HPCD concentration. The solubilization power of HPCD is dependent on the size and relative polarity of its cavity, and, unlike micelle-forming surfactants, HPCD has no critical micelle concentration. The partition mechanism was shown to be a valid approach for interpreting the solubilization activity of HPCD. The potential application of HPCD in the remediation of contaminated groundwater is briefly discussed.
• Angley, J. T., Brusseau, M. L., Miller, W. L., & Delfino, J. J. (1992). Nonequilibrium sorption and aerobic biodegradation of dissolved alkylbenzenes during transport in aquifer material: column experiments and evaluation of a coupled-process model. Environmental Science & Technology, 26(7), 1404-1410.
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  Abstract: First-order biodegradation rate constants decreased with decreasing number of C in the alkyl groups and exhibited a correlation with molecular structure as measured by molecular connectivity. For three series of isomers, the rate constant for the isomer with substituent in the ortho position was smaller than the rate constant for the other isomers. Predictions obtained with the coupled-process model, wherein sorption was assumed to be rate limited, matched the breakthrough curves better than did predictions obtained with a model wherein sorption was assumed to be instantaneous. Accordingly, the assumptions upon which use of the model was based, eg biodegradation occurs only in solution and without a significant acclimation period, and can be simulated with a first-order equation, appear to valid. -from Authors
• Brusseau, M. L. (1992). Factors influencing the transport and fate of contaminants in the subsurface. Journal of Hazardous Materials, 32(2-3), 137-143.
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  Abstract: The present status of research on the transport and fate of contaminants in the subsurface will be briefly reviewed. The discussion will center on solution-phase processes; other equally important processes (e.g., transformation reactions, vapor-phase processes, immiscible liquid-phase processes) are discussed in other papers presented in this issue.
• Brusseau, M. L. (1992). Nonequilibrium transport of organic chemicals: The impact of pore-water velocity. Journal of Contaminant Hydrology, 9(4), 353-368.
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  Abstract: The impact of variations in pore-water velocity on the nonequilibrium sorption and transport of organic chemicals was investigated. Miscible displacement experiments were performed with four organic chemicals (dichlorobenzene, naphthalene, tetrachloroethene and p-xylene) and three aquifer materials having low organic-carbon contents (0.02-0.1%). The results of the experiments were analyzed by using a one-dimensional advective-dispersive transport model, wherein sorption is considered instantaneous for a fraction of the sorbent and rate-limited for the remainder. An inverse relationship between the reverse sorption rate constant and the equilibrium sorption constant was evident for each of two velocities. However, there was an order-of-magnitude difference between the rate constants obtained at the two velocities. This suggests the existence of a time-scale effect, which must be accounted for when modeling the transport of organic solutes.
• Brusseau, M. L. (1992). Transport of rate-limited sorbing solutes in heterogeneous porous media: application of a one-dimensional multifactor nonideality model to field data. Water Resources Research, 28(9), 2485-2497.
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  Abstract: The purpose of this work was to evaluate the ability of a one-dimensional, multifactor nonideality model to represent the nonideal transport of sorbing solutes at the field scale. For this model the two-domain approach is used to represent heterogeneity, and sorption is represented as being essentially instantaneous for a portion of the sorbent and rate limited for the remainder. Data (breakthrough curves) obtained from four field experiments reported in the literature were used to test the performance of the model. With one exception, data from laboratory or field experiments were used to identify values for input paramters; the exception concerned an assumption of a uniform distribution of sorbent between the advective and nonadvective pore water domains. Specification of input parameters independent of the data being simulated allowed the model to be used in a predictive mode. -from Author
• Brusseau, M. L., Jessup, R. E., & Rao, P. S. (1992). Modeling solute transport influenced by multiprocess nonequilibrium and transformation reactions. Water Resources Research, 28(1), 175-182.
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  Abstract: The multiprocess nonequilibrium with transformation (MPNET) model is formulated for cases where nonequilibrium, caused by a combination of transport-related and sorption-related processes, and abiotic/biotic transformations can be described as first-order processes. The impact of the coupling of nonequilibrium and transformation reactions on solute transport is examined using selected illustrative examples. The performance of the model is evaluated by comparing predictions obtained with the model, where values for all model parameters are obtained independently, to a data set obtained from the literature. -from Authors
• Larsen, T., Christensen, T. H., & Brusseau, M. (1992). Predicting nonequilibrium transport of naphthalene through aquifer materials using batch determined sorption parameters. Chemosphere, 24(2), 141-153.
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  Abstract: Batch experiments with naphthalene sorption onto three aquifer materials with low organic carbon contents (≤ 0.025%) yielded kinetic parameters in accordance with the bicontinuum nonequilibrium model model (Kd, F, k2). About half of the sorption was instantaneous while the complementary sorptive fraction developed over 20 to 200 hours depending on the aquifer material. The equilibrium distribution (Kd) was linear as assumed by both the equilibrium and the bicontinuum nonequilibrium solute transport model. The batch determined kinetic parameters were successfully employed in predicting the breakthrough curves for the laboratory columns exposed to constant influent concentration of naphthalene. For two of the aquifer materials showing very little retardation of naphthalene (Kd ≈ 0.15 ml/g) the equilibrium and the bicontinuum nonequilibrium model gave comparable results, while the nonequilibrium model, using batch determined parameters, was superior to the equilibrium model in the case of the aquifer material showing Kd values of the order of 1 ml/g and a flow velocity of 75 m/y. © 1992.
• Brusseau, M. L. (1991). Cooperative sorption of organic chemicals in systems composed of low organic carbon aquifer materials. Environmental Science and Technology, 25(10), 1747-1752.
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  Abstract: The effect of a nonionic, low-polarity cosolute (tetrachloroethene) on the sorption of three nonionic, low-polarity organic chemicals (naphthalene, p-xylene, 1,4-dichlorobenzene) by two aquifer materials with low organic carbon contents (
• Brusseau, M. L. (1991). Transport of organic chemicals by gas advection in structured or heterogeneous porous media: development of a model and application to column experiments. Water Resources Research, 27(12), 3189-3199.
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  Abstract: The use of soil venting or vacuum extraction for remediation of contaminated soil has lead to an increased interest in modeling gas-phase processes. The majority of existing transport models have been developed assuming homogeneous porous media properties. It is well known, however, that the assumption of homogeneity will almost always be invalid for field systems. In addition, sorption has been described using the local equilibrium assumption. This assumption has also been shown to be invalid under certain conditions. A one-dimensional model is presented that accounts for a structured or heterogeneous porous medium and for rate-limited sorption. The model is designed for cases where transport occurs by advection and dispersion in the gas phase and where the liquid phase is immobile. A sensitivity analysis is presented, and parameter determination is discussed. -from Author
• Brusseau, M. L., & Rao, P. S. (1991). Influence of sorbate structure on nonequilibrium sorption of organic compounds. Environmental Science and Technology, 25(8), 1501-1506.
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  Abstract: We investigate the relationship between sorbate structure and nonequilibrium sorption. The rate-limited sorption of compounds representing eight classes of organic chemicals, including chlorinated benzenes, unsubstituted and alkyl-substituted aromatics, chlorinated ethenes and ethanes, chlorinated phenols, nitrogen heterocycles, s-triazines, substituted amides, and substituted ureas, was examined by use of a single sorbent (sandy aquifer material) and the miscible displacement technique. The breakthrough curves were analyzed by using a bicontinuum model wherein sorption is assumed instantaneous for a fraction of the sorbent and rate limited for the remainder. Sorbate structure was shown to exert minimal impact on the nature of rate-limited sorption for nonionic, low-polarity compounds comprising relatively simple structures and for ionogenic compounds in neutral form. In contrast, sorbate structure appeared to have a significant impact for compounds comprising more complex structures (i.e., pesticides). First-order reverse rate constants determined for the pesticides were at least 1 order of magnitude smaller than those of the non-pesticides. This difference was attributed to differences in degree of constraint on diffusion within the polymeric structure of organic matter.
• Brusseau, M. L., & Rao, P. S. (1991). Sorption kinetics of organic chemicals. Methods, models and mechanisms. SSSA Special Publication (Soil Science Society of America), 281-302.
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  Abstract: Rate-limited or, nonequilibrium, sorption of organic chemicals by natural sorbents (i.e., soils, sediments, and aquifer materials) has been a topic of interest for quite some time. The impact of nonequilibrium sorption on transport of organic chemicals in the subsurface has recently come under increased scrutiny as groundwater contamination has become a major issue. The purpose of this paper is to provide a brief review of the rate-limited sorption of organic chemicals by natural sorbents. The proposed processes held responsible for nonequilibrium sorption will be presented, as will a discussion of recent experiments whose results provide elucidation of rate-limiting mechanisms. Several models have been proposed to simulate sorption kinetics, and the transport of solutes influenced by nonequilibrium sorption; these will be reviewed. A large array of techniques are available for the study of sorption kinetics. However, much of this work has been oriented towards the study of inorganic chemicals. We will discuss two techniques that, in addition to the standard batch time study, have received the greatest amount of use in investigating nonequilibrium sorption of organic chemicals.
• Brusseau, M. L., & Reid, M. E. (1991). Nonequilibrium sorption of organic chemicals by low organic-carbon aquifer materials. Chemosphere, 22(3-4), 341-350.
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  Abstract: The objective of the work reported herein was to investigate nonequilibrium sorption of four representative organic chemicals by five aquifer materials comprised of low organic carbon (i.e., less than 0.1%). The results of miscible displacement experiments were analyzed using a one-dimensional advective-dispersive transport model, wherein sorption is considered instantaneous for a fraction of the sorbent and rate-limited for the remainder. An inverse correlation between the desorption rate constant and the equilibrium sorption constant was evident. It appears that all five aquifer materials exhibited similar nonequilibrium behavior, which suggests that the sorbent has only a secondary effect on the nature of nonequilibrium sorption. In addition, the data obtained for the aquifer materials were similar to data obtained for sorbents of higher organic-carbon contents.
• Brusseau, M. L., Jessup, R. E., & Rao, P. S. (1991). Erratum: Nonequilibrium sorption of organic chemicals: Elucidation of rate-limiting processes (Environ. Sci. Technol. (1991) 25 (134-142)). Environmental Science and Technology, 25(7), 1334-.
• Brusseau, M. L., Jessup, R. E., & Rao, P. S. (1991). Nonequilibrium sorption of organic chemicals: Elucidation of rate-limiting processes. Environmental Science and Technology, 25(1), 134-142.
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  Abstract: The results of experiments designed to identify the process(es) responsible for nonequilibrium sorption of hydrophobic organic chemicals (HOCs) by natural sorbents are reported. The results of experiments performed with natural sorbents were compared to rate data obtained from systems wherein rate-limited sorption was caused by specific sorbate-sorbent interactions. This comparison showed that chemical nonequilibrium associated with specific sorbate-sorbent interactions does not significantly contribute to the rate-limited sorption of HOCs by natural sorbents. Transport-related nonequilibrium was also shown to not be a factor for the systems investigated. Hence, attempts were made to interpret the data in terms of two, sorption-related, diffusive mass-transfer conceptual models: retarded intraparticle diffusion and intraorganic matter diffusion. The analyses provide strong evidence that intraorganic matter diffusion was responsible for the nonequilibrium sorption exhibited by the systems investigated in this paper.
• Brusseau, M. L., Larsen, T., & Christensen, T. H. (1991). Rate-limited sorption and nonequilibrium transport of organic chemicals in low organic carbon aquifer materials. Water Resources Research, 27(6), 1137-1145.
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  Abstract: Results of miscible displacement experiments performed at two pore water velocities and with very low solution-phase concentrations (30-60 μg l-1) were analyzed using a first-order mass transfer nonequilibrium model, as well as a model employing the local equilibrium assumption. Results of the analyses revealed sorption to be significantly rate limited, possibly by a diffusion-limited mechanism. The impact of rate-limited sorption on transport was dependent upon pore water velocity. The experiments performed at a faster velocity (~1 cm/h) could be successfully simulated only with the nonequilibrium model, whereas the equilibrium model was adequate for the slower-velocity (~0.2 cm/h) experiments. Comparison of experimental results to those reported in the literature revealed that time scale has a significant impact on the degree of nonequilibrium observed in, and on the values of rate constants determined from, experiments. -from Authors
• Brusseau, M. L., Wood, A. L., & Suresh, P. (1991). Influence off organic cosolvents on the sorption kinetics off hydrophobic organic chemicals. Eavironmental Science and Technology, 25(5), 903-910.
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  Abstract: A quantitative examination of the kinetics of Sorption of Hydrophobic organic chemicals by soils from mixed solvents reveals that the reverse sorption rate constant (k2) increases log-linearly with increasing volume fraction of organic cosolvent (fc). This relationship was expected, based on the existence of a log-log inverse relationship between k2 and the equilibrium sorption constant (Kp), and a log-linear inverse relationship between Kp and fc. These results are interpreted in terms of a conceptual model wherein sorption kinetics is controlled by diffusion of sorbate within the matrix of sorbent organic matter. Decreased polarity of the mixed solvent, caused by the addition of a cosolvent, appears to influence the conformation of the polymeric organic matter and, hence, the rate of sorbate diffusion. © 1991 American Chemical Society.
• Lee, L. S., Rao, P. S., & Brusseau, M. L. (1991). Nonequilibrium sorption and transport of neutral and ionized chlorophenols. Environmental Science & Technology, 25(4), 722-729.
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  Abstract: For a series of chlorophenols sorption nonequilibrium was assessed by fitting a bicontinuum sorption model to breakthrough curves measured by miscible displacement techniques. A single log-log inverse relationship was observed between the desorption rate coefficient (k2,h-1) and the equilibrium sorption constant (Kp, mL/g) for all chlorophenols as well as for a series of chlorobenzenes. This suggests that approach to sorption equilibrium for neutral and ionized chlorophenols is constrained in a manner similar to that for nonpolar hydrophobic organic chemicals. -from Authors
• Brusseau, M. L. (1990). Mass transfer processes and field-scale transport of organic solutes. Atomic Energy of Canada Limited, AECL (Report), 2(10308), 816-840.
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  Abstract: The influence of mass transfer processes, such as sorption/desorption and mass transfer between immiscible liquid and water, on the transport of organic solutes is discussed. Rate-limited sorption of organic solutes, caused by a diffusion-constrained mechanism, is shown to be significant under laboratory conditions. The significance of the impact of nonequilibrium sorption on field-scale transport is scale dependent. The impact of organic liquids on mass transfer and transport of organic solutes depends upon the nature of the solute and the nature and form of the organic liquid. For example, while retardation of nonionic solutes is decreased in mixed-solvent systems (i.e., systems comprised of water and a miscible organic liquid or an immiscible liquid present in concentrations below phase separation), the retardation of organic acids may, in some cases, increase with addition of a cosolvent. While the presence of an immiscible liquid existing as a mobile phase will reduce retention of organic solutes, the presence of of residual saturation of an immiscible liquid can significantly increase retention. A model is presented that incorporates the effects of retention resulting from residual saturation, as well as nonequilibrium sorption, on the transport of organic solutes.
• Brusseau, M. L., & Rao, P. S. (1990). Modeling solute transport in structured soils: a review. Geoderma, 46(1-3), 169-192.
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  Abstract: Solute transport in structured soils is and has been the focus of a significant research effort. Transport in such systems is often characterized by nonideal phenomena. These phenomena have usually been ascribed to the presence of immobile domains within the porous medium, which results in physical nonequilibrium. The phenomena can also, in some cases, be attributed to rate-limited sorption (i.e., sorption nonequilibrium). These processes are often modeled using a bicontinuum approach. It might be expected, for fieldscale problems, that nonequilibrium may be the result of more than one contributing process. A model that explicitly accounts for multiple sources of nonequilibrium would be preferable for such cases. The various models developed for simulating solute transport under nonequilibrium conditions are reviewed. © 1990.
• Brusseau, M. L., Jessup, R. E., Suresh, P., & Rao, C. (1990). Sorption kinetics of organic chemicals: Evaluation of gas-purge and miscible-displacement techniques. Environmental Science and Technology, 24(5), 727-735.
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  Abstract: Among the methods for investigating the sorption kinetics of organic chemicals, two of the most widely used are gas-purge (GP) and miscible-displacement (MD) techniques. There has been to date no critical evaluation of the general applicability or the equivalency of these two techniques, which was the purpose of this work. The viability of the GP technique is a function of the Henry's constant of the chemical and the sorptivity of the solute/sorbent combination; that of the MD technique is also a function of the latter and of the texture/structure of the sorbent. The GP technique appears ideal for investigating the sorption dynamics of organic contaminants in sediment/water systems, whereas the MD technique seems ideal for investigating the transport of solutes in soils and aquifer materials. The two techniques provided comparable values of sorption rate constants for similar systems.
• Wood, A. L., Bouchard, D. C., Brusseau, M. L., & Rao, P. S. (1990). Cosolvent effects on sorption and mobility of organic contaminants in soils. Chemosphere, 21(4-5), 575-587.
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  Abstract: Batch equilibrium and column miscible displacement techniques were used to investigate the influence of an organic cosolvent (methanol) on the sorption and transport of three hydrophobic organic chemicals (HOCs) - naphthalene, phenanthrene, and diuron herbicide - in a sandy surface soil (Eustis fine sand). Equilibrium sorption constant (K) values calculated from batch and column data exhibited an inverse log-linear dependence on the volume fraction (f(c)) of methanol in the mixed solvent. The slope of the log-linear plot was approximately equal to the logarithm of the ratio of the HOC solubilities in neat cosolvent and water. K values obtained from breakthrough curves (BTCs) were comparable to those estimated from equilibrium sorption isotherms. Long-term exposure to methanol-water mixtures had little effect on sorption and transport properties of the soil, but column retardation factors were influenced by the short-term solvent exposure history prior to solute elution.
• Brusseau, M. L., & Rao, P. S. (1989). Nonequilibrium and dispersion during transport of contaminants in groundwater: field-scale processes. Contaminant transport in groundwater. Proc. symposium, Stuttgart, 1989, 237-244.
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  Abstract: Several processes can cause nonideal behavior, including physical nonequilibrium, chemical nonequilibrium, intrasorbent diffusion, spatial variations in sorption coefficient, and spatial variability in hydraulic conductivity. Nonideality can be investigated with an analysis of data gathered from a recent natural gradient field experiment at Borden, Ontario. The nonideal behavior exhibited by the field data appears to result from spatial variability in hydraulic conductivity and sorption coefficients. The relative impact of the nonideality mechanisms can be qualitatively evaluated by comparing the effective dispersivity values associated with each process. The relative importance of the processes are scale dependent. Given the typical heterogeneous nature of most aquifer systems, and the manner in which water samples are usually taken (vertically-integrated), macrodispersion is most likely to be the predominant process influencing contaminant dispersion at the field scale. -from Authors
• Brusseau, M. L., & Rao, P. S. (1989). Sorption nonideality during organic contaminant transport in porous media. Critical Reviews in Environmental Control, 19(1), 33-99.
• Brusseau, M. L., & Rao, P. S. (1989). The influence of sorbate-organic matter interactions on sorption nonequilibrium. Chemosphere, 18(9-10), 1691-1706.
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  Abstract: Literature data on nonequilibrium sorption of organic solutes by natural sorbents were compiled. The solutes included a broad spectrum of nonpolar, hydrophobic organic chemicals (Type I) and polar/ionizable organic chemicals (Type II). Values for equilibrium sorption coefficient (Kp) and sorption rate constant (k) were determined for the data and were analyzed with the Linear Free Energy Relationship approach. The compiled data spanned approximately seven orders-of-magnitude in Kp values and approximately six orders-of-magnitude in k values. An inverse linear relationship was found between log k and log Kp. The intercept value for the Type I chemicals was larger than that for the Type II chemicals, which suggests that the sorption dynamics for the Type II chemicals were constrained to a greater degree than that for the Type I chemicals. After examining the experimental conditions under which the data were collected, and considering the nature of the sorbents and the sorbates, it was postulated that the following processes were responsible for the observed sorption nonequilibrium: intraorganic matter diffusion for Type I chemicals; intraorganic matter diffusion and chemical nonequilibrium for Type II chemicals. The rationale for the elimination of other mechanisms is discussed. A regression equation, relating k and Kp, is presented that may be used to estimate approximate values of the sorption rate constant for organic solutes. This provides a means to evaluate nonequilibrium potential and to attempt to predict nonequilibrium behavior. © 1989.
• Brusseau, M. L., Jessup, R. E., & Rao, P. S. (1989). Modeling the transport of solutes influenced by multiprocess nonequilibrium. Water Resources Research, 25(9), 1971-1988.
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  Abstract: The multiprocess nonequilibrium (MPNE) model is specifically formulated for cases where nonequilibrium is caused by a combination of transport- and sorption-related processes. Sensitivity analyses were performed to delineate the conditions under which the MPNE model reduces to the biocontinuum and to the local equilibrium models. These conditions are strongly controlled by the magnitude of the dimensionless rate parameters. Performance of the MPNE model was evaluated with several published data sets. An empirical regression equation was successfully used to estimate values for sorption rate constants required in the MPNE model. The MPNE model, with values for all parameters obtained from independent sources, predicted behaviour exhibited by the data. -from Authors
• Brusseau, M. L., Rao, P. S., Jessup, R. E., & Davidson, J. M. (1989). Flow interruption: A method for investigating sorption nonequilibrium. Journal of Contaminant Hydrology, 4(3), 223-240.
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  Abstract: A flow-interruption method for investigating sorption nonequilibrium is presented. The technique has a greater sensitivity to nonequilibrium than to traditional column experiments and hence provides a greater capacity to investigate nonequilibrium. The technique may provide more reliable determinations of kinetic parameter values. In some situations, the technique may be used to assist in the delineation of mechanism(s) responsible for sorption nonequilibrium. Use of the technique is demonstrated with miscible displacement of the herbicide 2,4-D through saturated soil columns. The sorption nonequilibrium exhibited by 2,4-D is suggested to be a result of intraorganic matter diffusion. Experimentally determined values of the sorption rate constant show an inverse relationship to organic matter content. © 1989.
• Nkedi-Kizza, P., Brusseau, M. L., Rao, P. S., & Hornsby, A. G. (1989). Nonequilibrium sorption during displacement of hydrophobic organic chemicals and ⁴⁵Ca through soil columns with aqueous and mixed solvents. Environmental Science and Technology, 23(7), 814-820.
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  Abstract: A series of miscible displacement experiments was conducted to investigate the significance of intraorganic matter diffusion (IOMD) as the rate-limiting step in sorption of organic and inorganic solutes during steady water flow in soil columns. Displacement studies were performed using Eustis surface soil and the same soil treated with hydrogen peroxide to reduce soil organic carbon content from 0.2% to < 0.01%. Two herbicides (diuron and atrazine) were also displaced with binary solvent mixtures containing varying fractions of methanol and water (0-50% methanol). A bicontinuum nonequilibrium sorption model was used to simulate the measured effluent breakthrough curves (BTCs) obtained by simultaneous displacement of a nonadsorbed tracer (tritiated water), an organic solute (herbicide), and a metal cation (45Ca). Support for IOMD as the rate-limiting step in sorption was provided by the following: (i) lack of asymmetry for the BTCs of tritiated water and 45Ca in contrast to the asymmetrical BTCs of the two herbicides for aqueous displacements; (ii) symmetrical BTCs for all solutes displaced through the soil that was treated to remove organic matter; (iii) decreasing asymmetry with increasing methanol content in the displacing solution. An analysis of the bicontinuum sorption model parameters also supported this conclusion.
• Lee, L. S., Rao, P. S., Brusseau, M. L., & Ogwada, R. A. (1988). Erratum. Environmental Toxicology and Chemistry, 7(12), 1047-.
• Lee, L. S., Rao, P. S., Brusseau, M. L., & Ogwada, R. A. (1988). Nonequilibrium sorption of organic contaminants during flow through columns of aquifer materials. Environmental Toxicology and Chemistry, 7(10), 779-793.
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  Abstract: Batch equilibrium and miscible displacement studies were conducted to investigate sorption and transport of trichloroethylene (TCE) and p-xylene in two sand aquifer materials low in organic carbon content. The utility of a bicontinuum (two-site) sorption model to describe the extent of sorption nonequilibrium during transport in saturated columns was evaluated. Model parameters estimated from the breakthrough curves (BTC) obtained at a high pore-water velocity (v = 24 cm/h) were used successfully to describe the BTC measured at a lower pore-water velocity (v = 6 cm/h). The assumption of local sorption equilibrium was valid at the lower velocity, and the measured BTC could be described by an equilibrium sorption model coupled to a convective-dispersive transport model. Values for column retardation factors estimated by fitting the two-site model to the BTC were comparable with those estimated from equilibrium sorption isotherms. BTC measured for displacement of binary mixtures (TCE plus p-xylene) and single-solute (TCE or p-xylene alone) were identical, suggesting that there is no competitive sorption between these two solutes. These column observations were consistent with sorption isotherm data. © 1988.

Presentations

• Brusseau, M. L. (2022). Invited Presentations. Invited Presentations.
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  Invited1. Brusseau, M.L. Occurrence and transport of PFAS in soil & groundwater. Presented to the Stony Brook Department of Geosciences Colloquium. March 10, 20222. Brusseau, M.L. PFAS adsorption at air-water interfaces. The International PFAS Summit. Tubingen, Germany. April 4-5, 2022.3. Brusseau, M.L. Occurrence and transport of PFAS in soil & groundwater. Presented to Tucson Mission Gardens, Tucson, AZ. July 15, 2022.4. Brusseau, M.L. PFAS transport in source zones. Presented at the International Cleanup Conference. Adelaide, Australia. September 11-13, 2022.5. Brusseau, M.L. PFAS presence in soil and leaching potential to groundwater, with a focus on MAR. Managed Aquifer RechargeWebinar, American Ground Water Trust. October 12, 2022.
• Brusseau, M. L. (2022). Volunteered Presentations. Volunteered Presentations.
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  Volunteered Presentations1. Honan, J., Huth, H., Megdal, S., Tuller, M., Maximillian, J., and Brusseau, M.L. An ecological assessment of the upper Santa Cruz river using environmental management tools. International Society of Exposure Science Annual Meeting. Lisbon, Portugal. September 25-29, 2022.2. Guo, B., J. Zeng, M.L. Brusseau, and Y. Zhang. A screening model for quantifying PFAS leaching in the vadose zone and mass discharge to groundwater. Presented at the EGU General Assembly 2022. May 23–27, 2022.3. Guo, B., Brusseau, M.L., Higgins, C., and Hatton, J. Development and Demonstration of PFAS-LEACH—A Comprehensive Decision Support Platform for Predicting PFAS Leaching in Source Zones. SERDP & ESTCP PFAS Meeting. Long Beach, CA. July 18-22, 2022.4. Briseno Arellano, A.D., Yao, T-M., Miczarek, M., and Brusseau, M.L. Column experiments to assess consolidation behaviour at different initial irrigation rates in copper heap leaching. Heap Leach Solutions Conference. Sparks, NV. October 16–18, 2022.5. Mohamed, R.A.M., Hitzelburger, M., Khan, N.A., and Brusseau, M.L., Carroll, K.C. Modeling of perfluorooctanesulfonic acid contaminant transport in saturated heterogeneous media and evaluation of back-diffusion retention and removal effects. 67th Annual New Mexico Water Conference. Las Cruces, NM. October 26-27, 2022.6. Carroll, K.C., Hitzelburger, M., Khan, N.A., Mohamed, R.A.M., and Brusseau, M.L. Perfluorooctane sulfonic acid (PFOS) transport and mass flux reduction / mass removal in homogeneous versus heterogeneous systems. Soil Science Society of America Annual Conference. SSSA Annual Conference, November 08, 2022.7. Guo, B., M.L. Brusseau, C. Higgins, and J. Hatton. Development and demonstration of PFAS-LEACH—A comprehensive decision support platform for predicting PFAS leaching in source zones. SERDP & ESTCP Annual Conference. Arlington, VA. November 29-December 2, 2022.8. Alghzawi, M., Root, R., Song, B., De Garcia, X., Brusseau, M.L., and Chorover, J. Enrichment and depletion of toxic metal(loid)s in sulfidic mine tailings profiles subject to weathering under variable climate. NIEHS Superfund Annual Conference. Raleigh, NC. December 14-16, 2022.9. Song, B., Root, R., Alghzawi, M., De Garcia, X., Brusseau, M.L., and Chorover, J. Parent material weathering drives arsenic bioavailability. NIEHS Superfund Annual Conference. Raleigh, NC. December 14-16, 2022.10. Guo, B., Saleem, H., and Brusseau, M.L. Predicting air–water and NAPL–water interfacial adsorption of PFAS and hydrocarbon surfactants in multicomponent solutions. American Geophysical Union Annual Conference. Chicago, IL. December 12-16, 2022.11. Bigler, M., Guo, B., and Brusseau, M.L. The impacts of air water interfacial area on surfactant transport at low water saturations. American Geophysical Union Annual Conference. Chicago, IL. December 12-16, 2022.12. Borkan, W., El Ouni, A., Root, R., Chorover, J., Taffett, M., and Brusseau, M.L. Measuring sorption capacity and hydraulic flow properties of samples from a uranium-contaminated fractured-rock aquifer in Livermore, California. American Geophysical Union Annual Conference. Chicago, IL. December 12-16, 2022.
• Brusseau, M. L. (2021). Invited Presentation: Modeling the Retention and Transport of PFAS in the Vadose Zone. PFAS Management into the Future Conference, organized by the Australasian Land & Groundwater Association, April 28, 2021..
• Brusseau, M. L. (2021). Invited Presentation: Occurrence and Transport of PFAS in Soil & Groundwater. New Mexico State University Sigma Xi Science Cafe, October 19, 2021..
• Brusseau, M. L. (2021). Invited Presentation: PFAS Characterization, Fate, and Transport. PFAS Experts Symposium, organized by the Remediation Journal, June 29-July 1, 2021.
• Brusseau, M. L. (2021). Invited Presentation: PFAS Migration in the Vadose Zone: A Case Study Illustrating the Complexities of Solute Transport in Soil. Soil Science Society of America Annual Meeting, November 7-10, 2021..
• Brusseau, M. L. (2021). Invited Presentation: The Complexities of Remediation for a Chlorinated-Solvent Contaminated Site: a 35-year Case Study. Soluciones a la Contaminación de Suelo y Acuíferos (SCSA_2021), organized by the Universidad Nacional Autónoma de México, September 29-30, 2021.
• Brusseau, M. L. (2021). Invited Presentation: The Influence of Source Types on Per- and Polyfluoroalkyl Substances Concentrations and Distributions in Soil. Soil Science Society of America Annual Meeting, November 7-10, 2021..
• Brusseau, M. L. (2021). Invited Presentation: The Retention and Transport of PFAS in Soil and the Vadose Zone. NEBC PFAS Workshop: Fundamentals and Perspectives, organized by Haley & Aldrich, Inc., October 13, 2021..
• Brusseau, M. L. (2021). Volunteered Presentation: A screening model for quantifying PFAS leaching in the vadose zone and mass discharge to groundwater. American Geophysical Union Annual Meeting, December 13-17, 2021.
• Brusseau, M. L. (2021). Volunteered Presentation: Characterization of One and Two Dimensional Transport of Perfluorooctane Sulfonic Acid in Homogeneous and Heterogeneous Sands. Soil Science Society of America Annual Meeting, November 7-10, 2021..
• Brusseau, M. L. (2021). Volunteered Presentation: Modeling Back-Diffusion Impacts on Perfluorooctane Sulfonic Acid (PFOS) Contaminant Transport. RemPlex Summit 2021 Global Summit on Environmental Remediation, November 8-12..
• Guo, B., & Brusseau, M. L. (2021). Volunteered Presentation: Development and Demonstration of PFAS-LEACH—A Comprehensive Decision Support Platform for Predicting PFAS Leaching in Source Zones. SERDP-ESTCP Annual Symposium, November 29-December 3, 2021.
• Brusseau, M. L. (2020, 2020). 14 Volunteered Presentations at International Conferences. Various National-International Conferences. Virtual: AGU, GSA, SERDP, ISPM.
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  List of the 14 presentations:1.Guo, B., Zeng, J., and Brusseau, M.L. Mathematical modeling of the fate and transport of per- and polyfluoroalkyl substances (PFAS) in the vadose zone. Presented at the Annual Meeting of the International Society for Porous Media (Virtual). August 31 to September 4, 2020.2.Brusseau, M.L. and Guo, B. PFAS Retention and Leaching in Soils & the Vadose Zone. Presented at the Geological Society of America Annual Meeting (Virtual), October 26-30, 2020.3.Guo, B. and Brusseau, M.L. Mathematical modeling of the long-term retention and leaching of PFAS in the vadose zone. Presented at the Geological Society of America Annual Meeting (Virtual), October 26-30, 2020.4.Brusseau, M.L. and Guo, B. PFAS Retention and Leaching in the Vadose Zone. Presented at the annual SERDP-ESTCP Symposium (Virtual). November 30-December 4, 2020.5.Guo, B. and Brusseau, M.L. Mathematical modeling of the long-term retention and leaching of PFAS in the vadose zone. Presented at the annual SERDP-ESTCP Symposium (Virtual). November 30-December 4, 2020.6.Van Glubt, S. And Brusseau, M.L. The Impact of PFAS Adsorption to NAPL-Water Interfaces on PFAS Retention and NAPL Mobilization. Presented at the annual SERDP-ESTCP Symposium (Virtual). November 30-December 4, 2020.7.Bigler, M., Guo, B., and Brusseau, M.L. Impact of PFAS on Water Distribution in the Vadose Zone. Presented at the annual SERDP-ESTCP Symposium (Virtual). November 30-December 4, 2020.8.Araujo, J.B., Brusseau, M.L., Meixner, T., Simunek, J., and Dontsova, K. Influence of environmental factors on fate and transport of insensitive munitions (IM) constituents. Presented at the annual SERDP-ESTCP Symposium (Virtual). November 30-December 4, 2020.9.Brusseau, M.L. and Guo, B. PFAS Retention and Leaching in the Vadose Zone. Presented at the American Geophysical Union Annual Meeting (Virtual). December 1-17, 2020.10.Brusseau, M.L. and Guo, B. Characterizing PFAS Retention and Transport in Soil. Presented at the American Geophysical Union Annual Meeting (Virtual). December 1-17, 2020.11.Guo, B. and Brusseau, M.L. Mathematical modeling of the long-term retention and leaching of PFAS in the vadose zone. Presented at the American Geophysical Union Annual Meeting (Virtual). December 1-17, 2020.12.Guo, B. and Brusseau, M.L. A mathematical model for the release, transport, and retention of per- and polyfluoroalkyl substances (PFAS) in the vadose zone. Presented at the American Geophysical Union Annual Meeting (Virtual). December 1-17, 2020.13.Zeng, J., Brusseau, M.L., and Guo, B. Modeling the Long-term Retention and Leaching of PFAS in the Vadose Zone. Presented at the American Geophysical Union Annual Meeting (Virtual). December 1-17, 2020.14.Emin, A., El Ouni, A., Zhong, H., and Brusseau, M.L. Uranium Biosequestration and Biosequestered Uranium Re-oxidation Multicomponent Transport Modeling. Presented at the American Geophysical Union Annual Meeting (Virtual). December 1-17, 2020.
• Brusseau, M. L. (2020, January 16 2020). Invited Presentation: Transport of Per- and Poly-fluoroalkyl Substances in the Vadose Zone. Annual TIAA Technical Exchange Meeting. Tucson, AZ: US EPA.
• Brusseau, M. L. (2020, March 13, 2020). Invited Presentation: PFAS Occurrence and Transport in the Subsurface. Arizona Department of Environmental Quality Seminar. VIrtual: Arizona Department of Environmental Quality.
• Brusseau, M. L. (2020, September 16, 2020). Invited Presentation: PFAS Retention and Leaching in the Vadose Zone. The Science of PFAS Conference. Virtual: The Air & Waste Management Association.
• Brusseau, M. L. (2020, eptember 29-October 1, 2020). Invited Presentation: PFAS Transport in the Vadose Zone. Annual University Consortium Fall Focus Meeting. Virtual: University Consortium (Colorado State Univeristy host).
• Brusseau, M. L. (2019, 2019). Scholarly Presentations-- Aggregated List. Scientific Conferences.
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  1. Wang, Y., Hyatt, L., Qin, C., Brusseau, M.L., and Dontsova, K., Saturated Column Transport Studies of Insensitive and Traditional Munitions in Soil. Presented at the Soil Science Society of America Annual Meeting, San Diego, CA, January 6-9, 2019.2. Brusseau, M.L. Comprehensive Retention Model for PFAS Transport in Subsurface Systems. Presented at the America Chemical Society Annual Meeting, San Diego, CA, August 25-29, 2019.3. Van Glubt, S., Ni, Y., Wang, Y., and Brusseau, M.L. The Influence of multi-process retention on the transport of perfluorooctancesulfonic acid (PFOS) in the presence of non-aqueous phase liquids (NAPLs). Presented at the America Chemical Society Annual Meeting, San Diego, CA, August 25-29, 2019.4. Van Glubt, S., and Brusseau, M.L. Retention and Transport of PFAS in Source Zones. Presented at the NIEHS Superfund Research Program Annual Meeting, Seattle, WA, November 18-20, 2019.5. Dontsova, K., Taylor, S., Qin, Chao., Wang, Y., Hunt, E., Brusseau, M., and Jiri, Simunek. Photo-transformation, Sorption, Transport, and Fate of Mixtures of NTO, DNAN, and Traditional Explosives as Function of Climatic Conditions. Presented at the Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP) Symposium, Wash, DC, December 3-5, 2019. 6. Brusseau, M.L., PFAS Transport in Porous Media with Multi-process Retention. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.7. Van Glubt, S., and Brusseau, M.L., The impact of PFAS Adsorption to NAPL-water interfaces on PFAS Retention and NAPL Mobilization. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.8. Bigler, M., Van Glubt, S., Guo, Bo., and Brusseau, M.L. Impact of PFAS on Water Distribution in the Vadose Zone. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.9. Lyu, Y., and Brusseau, M.L. Adsorption at the Air-Water Interface during Transport in Unsaturated Porous Media. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.10. El Ouni, A., Guo, B., and Brusseau, M.L. Measuring Air-Water Interfacial Area for Porous Media Using the Aqueous Interfacial Partitioning Tracer Test Method. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.11. Alshebel, B.H., and Brusseau, M.L. Use of QSPR to Predict PFAS Adsorption to Carbonaceous Materials. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.12. Emin, A., El Ouni, A., Zhong, H., and Brusseau, M.L. Multicomponent Transport Modeling of Uranium Biosequestration. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.13. Liu, H., Yang, J., Ma, J., Li, P., Zhou, Q., and Brusseau, M.L. Investigation of DNAPL Contaminant Migration Process in a Sandbox Using Electrical Resistivity Tomography. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.14. Jiang, H., Guo, B., and Brusseau, M.L. Pore-Scale Modeling of Fluid-Fluid Interfacial Area in Variably Saturated Porous Media Containing Micro-Scale Surface Roughness. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.15. Huang, D., Wang, G., and Brusseau, M.L. The Co-transport of PFAS and Cr(VI) in Porous Media. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.16. Araujo, J.B., Arthur, J., Brusseau, M.L. Simunek, J., Taylor, S., and Dontsova, K. Integrative Approach to Assessing Fate of Munitions in the Environment, San Francisco, CA, December 9-13, 2019.17. Wang, Y., Khan, N., Yan, N., Glubt, S.V., Carroll, K.C., and Brusseau, M.L. Nonideal Transport and Extending Elution Tailing of PFOS in Soil and Aquifer Sediment. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 9-13, 2019.
• Brusseau, M. L. (2019, February). The Occurrence and Fate of Per- and Poly-fluoroalkyl Substances (PFAS) in the Environment.. Presented at the University of Arizona Water Resources Research Center, Tucson, AZ, February 20, 2019..
• Brusseau, M. L. (2018, 2018). Invited Presentations. See description.
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  1. Brusseau, M.L. In-situ Biosequestration of Uranium: Monument Valley Project. Presented at the Restoring Ke’ Conference on the Impacts of Uranium on Tribal Lands, sponsored by the Colorado Plateau Foundation and the National Institute of Environmental Health Sciences, Tucson, AZ, April 23, 2018.2. Brusseau, M.L. Contaminants in the Subsurface Environment. Seminar presented at the Mel and Enid Zuckerman College of Public Health, University of Arizona, November 14, 2018.
• Brusseau, M. L. (2018, 2018). Volunteered Presentations. See description.
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  1. Brusseau, M.L., Virgone, K., and El Ouni, A. Development of an Effective Integrated Framework for Assessing Mining Sustainability. Presented at the Arizona International Human-Environment Observatory (OHMI) Conference, sponsored by the French CNRS Institute of Ecology and Environment (INEE) and the CNRS Institute of the Social Sciences (INSHS), Tucson, Arizona, April 12, 2018.2. Brusseau, M.L. Comprehensive Retention Model for PFAS Transport in Subsurface Systems. Presented at the American Geophysical Union Annual Meeting, Washington, DC, December 10-14, 2018.3. Yan, N., M.L. Brusseau, W. Chen, S. Van Glubt, Y. Wang, B. Dungan, K.C. Carroll, F.O. Holguirn. The Retention of PFAS at the Air-water Interface during Transport in Unsaturated Porous Media. Presented at the American Geophysical Union Annual Meeting, Washington, DC, December 10-14, 2018.4. Van Glubt, S., Yan, N., Y. Wang, M.L. Brusseau. The Influence of Multi-process Retention on the Transport of Perfluorooctanesulfonic acid (PFOS) in the Presence of Non-aqueous Phase Liquids (NAPLs). Presented at the American Geophysical Union Annual Meeting, Washington, DC, December 10-14, 2018.5. Wang, Y. and M.L. Brusseau. Transport of Graphene and Graphene Oxide in Saturated Porous Media. Presented at the American Geophysical Union Annual Meeting, Washington, DC, December 10-14, 2018.6. Carroll, K.C., L. Bridges, M.L. Brusseau, R.A. M. Mohamed, and C. Papelis. Persulfate Activation and Enhanced Degradation of 1,4-Dioxane in Water using Manganese Amendment for In Situ Chemical Oxidation. Presented at the American Geophysical Union Annual Meeting, Washington, DC, December 10-14, 2018.
• Brusseau, M. L. (2017, June 12). Invited Presentation. Risk eLearning Webinar – Analytical Tools and Methods: Session III – Fate and Transport of Contaminants. International webinar: NIEHS and US EPA.
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  The Integrated Contaminant Elution and Tracer Test for Improved Characterization of Mass Transfer, Attenuation, and Mass Removal.
• Brusseau, M. L. (2017, Various). Participant in 11 volunteered presentations at various international and national scientific society conferences. Various- see itemized list. Various: Various.
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  Here is the list of individual presentations:1. Zhong, H., A. El Ouni, D. Gutierrez, R. Johnson, R. Root, J. Chorover, and M.L. Brusseau. Pilot-Scale In-situ Biosequestration of Uranium in Groundwater at the Monument Valley UMTRA Site. Presented at the 9th International Perspective on Water Resources and the Environment. Environment & Water Resources Institute (EWRI) and American Society of Civil Engineers (ASCE); Wuhan, China, Jan 4-6, 2017.2. Zhong, H., Brusseau, M.L. Heterogeneous Activation of Persulfate using Fe3O4 for Degradation of Refractory Organic Compounds in Water. Presented at SEES 2017: 6th Annual International Conference on Sustainable Energy and Environmental Sciences, Singapore, March 6-7, 2017.3. Bridges, L., M.L. Brusseau, and K.C. Carroll. Manganese Dioxide Activation of Sodium Persulfate for Contaminant Oxidation. Presented at the NM WRRI’s 62nd Annual New Mexico Water Conference, Hidden Realities of New Water Opportunities, Socorro, NM., Aug. 15-16, 2017. 4. Hard, H.R., M.L. Brusseau, and M. Ramirez-Andreotta. Safety for Grazing Animals: Metal Concentrations of Soil and Plants at a Sealed, Arid Landfill. Presented at the annual Soil Science Society of America Meeting, Tampa, Florida. October 22-25, 2017.5. Brusseau, M.L., Z. Guo, K.C. Carroll. Methods for Characterizing Mass Transfer, Attenuation, and Mass Removal in Support of Subsurface Remedial Action Design, Operation, and Performance Evaluation. Presented at the SERDP and ESTCP Symposium, Washington, DC, November 28-30, 2017.6. Briseño Arellano, A.D., M. Milczarek, M. Yao, M.L. Brusseau. The effect of initial irrigation conditions on heap leaching efficiency. Presented at the Annual Meeting of the American Geophysical Union, San Francisco, CA, December 11-15, 2017.7. El Ouni, A., H. Zhong, and M.L. Brusseau. In-situ Biosequestration of Uranium: Monument Valley Project. Presented at the Annual Meeting of the American Geophysical Union, San Francisco, CA, December 11-15, 2017.8. Araujo, J.B. and M.L. Brusseau. The Impact of Solid Surface Features on Fluid-Fluid Interface Configuration. Presented at the Annual Meeting of the American Geophysical Union, San Francisco, CA, December 11-15, 2017.9. Yan, N., M.L. Brusseau, and F. Liu. Influence of subsurface environment on oxidant activation and 1,4-dioxane degradation by in-situ chemical oxidation. Presented at the Annual Meeting of the American Geophysical Union, San Francisco, CA, December 11-15, 2017.10. Chen, W., N. Yan, Y. Lyu, X. Fu, K.C. Carroll, F.O. Holguin, M.L. Brusseau. Adsorption and Retardation of PFASs in Soils. Presented at the Annual Meeting of the American Geophysical Union, San Francisco, CA, December 11-15, 2017.11. Brusseau, M.L. Assessing Potential Additional PFAS Retention Processes in the Subsurface. Presented at the Annual Meeting of the American Geophysical Union, San Francisco, CA, December 11-15, 2017.
• Brusseau, M. L. (2016, Feb). Invited Talk: Pilot Testing of In-situ Biostimulation for Biosequestration of Uranium in Groundwater. National Meeting of the Society for Mining, Metallurgy & Exploration.
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  Invited Talk
• Brusseau, M. L. (2016, Nov). Invited Talk: Hydrobiogeochemistry: The Transport and Fate of Constituents in the Subsurface. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America Annual Meeting.
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  Invited Talk
• Brusseau, M. L. (2016, annual). Volunteered Presentations = 15 total. Various National Science Meetings.
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  Total of 15 volunteered presentations
• Brusseau, M. L. (2015, 2015). Volunteered Presentations. Multiple Events--- 16 total.
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  Here is the list of presentations:267. Danny, K.R., Taffet, M.J., Brusseau, M.L., and Chorover, J. Dominant Attenuation Processes Influencing Uranium Transport In Groundwater At A Retired Explosives Test Site. Presented at the International Nuclear Waste Management Conference WM2015, Phoenix, AZ, March 15-19, 2015. 268. Wilkinson, S.T., Moreno Ramírez, D., Chief, K., Neilson, J. W., Brusseau, M.L., Artiola, J., and Maier, R.M. The Center for Environmentally Sustainable Mining: An Industry-Academic Cooperative to Promote Environmental Stewardship of Mining Sites. Presented at the NIEHS Superfund Research Program Annual Meeting, San Juan, Puerto Rico, November 18 - 20, 2015.269. Danny, K.R., Taffet, M.J., Brusseau, M.L., and Chorover, J. Attenuation and Transport Mechanisms of Depleted Uranium in Groundwater at Lawrence Livermore National Laboratory (LLNL) Site 300 Building 812. Presented at the American Indian Science and Engineering Society National Conference, Phoenix, AZ, November 19-21, 2015. 270. Araujo, J.B. and Brusseau, M.L. Identification of Novel Fluid-Fluid Interfacial Area in Geologic Media. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.271. Carroll, K.C. Comparison of Interfacial Partitioning Tracer Test and X-ray Microtomography Measurements of Immiscible Fluid-Fluid Interfacial Areas within the Identical System. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.272. Danny, K.R., Taffet, M.J., Brusseau, M.L., and Chorover, J. Attenuation and Transport Mechanisms of Depleted Uranium in Groundwater at LLNL Site 300. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.273. Guo, Z. and Brusseau, M.L. The Impact of Well-Field Configuration and Permeability Heterogeneity on Contaminant Mass Removal and Plume Persistence. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.274. LaBrie, H., Brusseau, M. L., and Huth, H. Influence of the Nogales International Wastewater Treatment Plant on surface water in the Santa Cruz River and local aquifers. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.275. Li, M., Brusseau, M.L., Yan, N., and Wan, L. Measuring NAPL-Water Interfacial Areas to Evaluate the Effectiveness of In-Situ Chemical Oxidation for DNAPL-Contaminated Source Zones: A Two-Dimensional Flow Cell Study. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.276. Mainhagu, J., Morrison, C., and Brusseau, M.L. Using vapor phase tomography to measure the spatial distribution of vapor concentrations and flux for vadose-zone VOC sources. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.277. Miao, Z., Gu, X., Lu, S., Brusseau, M. L., Yan, N., Qiu, Z., and Sui, Q. Tetrachloroethene degradation by reducing-agent enhanced Fe(II)/Fe(III) catalyzed percarbonate. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.278. Ramirez-Andreotta, M.D., Brusseau, M.L., Artiola, J.F., Maier, R.M., and Gandolfi, A.J. Building a Co-Created Citizen Science Program with Community Members Neighboring a Hazardous Waste Site . Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.279. Ramirez-Andreotta, M.D., Brusseau, M.L., Artiola, J.F., Maier, R.M., and Gandolfi, A.J. Environmental Research Translation: Enhancing interactions with communities at contaminated sites. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.280. Tabatabaei, Sayyed-Hassan, Zhong, H., Gutierrez, D., Field, J., and Brusseau, M.L. Impact of Electron Donor selection on In-situ Biosequestration of Uranium . Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.281. Yan, N., Brusseau, M.L., Zhong, H., and Li, M. The natural activation ability of subsurface media during in-situ chemical oxidation of 1,4-dioxane. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.282. Zhong, H., Gutierrez, D., Abel, E., Johnson. R., Root, R., Chorover, J., and Brusseau, M.L. Pilot-Scale In-situ Biosequestration of Uranium in Groundwater at the Monument Valley UMTRA Site. Presented at the American Geophysical Union Annual Meeting, San Francisco, CA, December 14-18, 2015.
• Brusseau, M. L. (2015, dec). Invited presentation. American Geophysical Union Annual Meeting. San Fran CA.
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  Chemical Hydrogeology: Fifty Years of Advances, Breakthroughs, and Innovations
• Brusseau, M. L. (2013, 10). Impact of Mass-transfer Processes on Removal and Persistence of Groundwater Contaminant Plumes. Invited Talk presented at the Annual Meeting of the The University Consortium for Field-Focused Groundwater Research. Denver, CO.
• Brusseau, M. L. (2013, 12). Persistent Groundwater Contaminant Plumes: Processes, Characterization, and Case Studies. Invited Talk presented at the Region 9 USEPA Seminar Series. San Francisco CA.
• Brusseau, M. L. (2013, Various). Thirteen volunteered Presentations at National Science Society Meetings. Various- see internal list.
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  1. Wilkinson, S.T., Loh, M., Lothrop, N., Brusseau, M.L., Maier, R.M. The University of Arizona Superfund Research Program: Research Translation in Action at the Iron King Mine Humboldt Smelter Superfund Site. Presetned at the NIEHS Superfund Research Program Annual Meeting, Baton Rouge, LA, October 15-17, 2013.2. Araujo, J.B., Tuller, M. and Brusseau, M.L. Determination of Film, Capillary, and Total Air- Water Interfacial a Using X-Ray Microtomography. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.3. Carroll, K.C., McDonald, K., Marble, J. and Brusseau, M.L. The Impact Of Immiscible Displacement And Fluid Configuration On Pore-Scale Two and Three-Phase Distribution In Porous Media Systems. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.4. El Ouni, A. and Brusseau, M.L. A Dual-Surfactant Approach for the Interfacial Partitioning Tracer Test Measurement Of Air-Water Interfacial Area. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.5. Guo, Z. and Brusseau, M.L. The Impact of Well-Field Configuration on Plume Persistence. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.6. Lin, D., Jin, M., Ma, B., Liu, Y. and Brusseau, M.L. Using Tracer Tests To Estimate Vertical Recharge And Evaluate Influencing Factors For Irrigated Agricultural Systems. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.7. Mainhagu, J. and Brusseau, M.L. Estimating Initial Source-Zone Contaminant Mass Based On Fitting Mass-Depletion Functions To Contaminant Mass Discharge Data: Testing Method Efficacy With SVE Operations Data. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.8. Marble, J.C., Carroll, K.C., Plaschke, M., Brinker, F. and Brusseau, M.L. Development of a Persistent Reactive Treatment Zone For Containment Of Sources Located In Lower-Permeability Strata. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.9. Matthieu, D.E., Plaschke, M., Carroll, K.C., Brinker, F. and Brusseau, M.L. Persistence of a Groundwater Contaminant Plume After Hydraulic Source Containment at a Chlorinated- Solvent Contaminated Site. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.10. Zhong, H., El Ouni, A., Lin, D., Wang, B. and Brusseau, M.L. Interfacial Partitioning Tracer Test Measurement Of NAPL-Water Interfacial Areas In Porous Media Under Two-Phase Flow Condition. Presented at the American Geophysical Union National Meeting, San Francisco, CA, December 9-13, 2013.11. Dontsova, K. Taylor, S., Pesce-Rodriguez, R., Brusseau, M.L. Dissolution and Fate of IM Compounds in the Environment. Presented at the Joint Army-Navy-NASA-Air Force Subcommittee Meeting, Charleston, SC, December 9-12, 2013.12. Ramirez-Andreotta, M.D., Brusseau, M.L., Artiola, J., Gandolfi, A.J., and Maier, R.M. Environmental Research Translation at Contaminated Sites for Improving Community Engagement and Citizen Science: The Gardenroots Case Study. Presented at the NIEHS Environmental Health Disparities & Environmental Justice Meeting, Raleigh-Durham, NC July 29-31, 2013.13. Tick, G. and Brusseau, M.L. Factors Influencing the Transport and Remeidation of Contaminats at Hazardous Waste Sites. Presented at the Annual Meeting of the Soil Science Society of America, Tampa, FL, November 3-6, 2013.
• Brusseau, M. (2012, April). Hazardous Waste Sites in Arizona: Impacts on Water Resources Sustainability. Hydrology and Water Resources Dept. Seminar. Tucson, AZ.
• Brusseau, M. (2012, April). Remediation of Chlorinated-solvent Contaminated Groundwater. Motorola 52nd St. Superfund Site Community Information Group. Phoenix, AZ: U.S. Environmental Protection Agency.

Others

• Ramirez-Andreotta, M., Artiola, J., Brusseau, M., & Maier, R. (2012, December). Gardenroots: Protecting Communities Neighboring Contamination- A Transdisciplinary Approach to Deteremine the Accumulation of Arsenic in Vegetables. International e-seminar, hosted by the U.S. EPA and NIEHS.
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  Exact Date: 12/31/2012
• Brusseau, M. (2011, December). Field Work at a Hazardous Waste Site: Challenges, Rewards, and Unexpected Outcomes. AGU Hydrology Section Newsletter.
• Callegary, J., Paretti, N., Gray, F., Norman, L., Beisner, K., Eddelman, K., Matti, L., Papoulias, D., Van, R. C., Bell, J., McAndrew, R., Lincicome, A., Brusseau, M., Alvarez, D., Scott, C., Vandervoet, P., & Medgal, S. (2011, March). Linking hydrology, geology, chemistry, and biology in the Upper Santa Cruz River Basin. Santa Cruz River Researcher s Day.
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  Exact Date: 03/29/2011
• McAndrew, R., Callegary, J., & Brusseau, M. (2011, January). Groundwater Contaminant Transport Modeling In the Upper Santa Cruz Basin. Santa Cruz River Researcher's Day.
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  Exact Date: 1/1/2011
• Russo, A., Aykol, N., Schnaar, G., Johnson, G., Yolcubal, I., & Brusseau, M. (2011, December). Nonideal Sorption-Desorption and Extensive Elution Tailing. Annual Meeting of the American Geophysical Union.
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  Exact Date: 12/5-12/9/2011