Klaus Rathfelder

Tufts University, Medford, MA, United States

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Publications (22)56.4 Total impact

  • Journal of Environmental Engineering-asce - J ENVIRON ENG-ASCE. 01/2006; 132(1).
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    ABSTRACT: A pilot-scale demonstration of surfactant-enhanced aquifer remediation (SEAR) was conducted to recover dense nonaqueous phase liquid (DNAPL) tetrachloroethene (PCE) from a sandy glacial outwash aquifer underlying a former dry cleaning facility at the Bachman Road site in Oscoda, MI. Part one of this two-part paper describes site characterization efforts and a comprehensive approach to SEAR test design, effectively integrating laboratory and modeling studies. Aquifer coring and drive point sampling suggested the presence of PCE-DNAPL in a zone beneath an occupied building. A narrow PCE plume emanating from the vicinity of this building discharges into Lake Huron. The shallow unconfined aquifer, characterized by relatively homogeneous fine-medium sand deposits, an underlying clay layer, and the absence of significant PCE transformation products, was judged suitable for the demonstration of SEAR. Tween 80 was selected for application based upon its favorable solubilization performance in batch and two-dimensional sand tank treatability studies, biodegradation potential, and regulatory acceptance. Three-dimensional flow and transport models were employed to develop a robust design for surfactant delivery and recovery. Physical and fiscal constraints led to an unusual hydraulic design, in which surfactant was flushed across the regional groundwater gradient, facilitating the delivery of concentrations of Tween 80 exceeding 1% (wt) throughout the treatment zone. The potential influence of small-scale heterogeneity on PCE-DNAPL distribution and SEAR performance was assessed through numerical simulations incorporating geostatistical permeability fields based upon available core data. For the examined conditions simulated PCE recoveries ranged from 94to 99%. The effluent treatment system design consisted of low-profile air strippers coupled with carbon adsorption to trap off-gas PCE and discharge of treated aqueous effluent to a local wastewater treatment plant. The systematic and comprehensive design methodology described herein may serve as a template for application at other DNAPL sites.
    Environmental Science and Technology 04/2005; 39(6):1778-90. · 5.26 Impact Factor
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    ABSTRACT: A pilot-scale demonstration of surfactant-enhanced aquifer remediation (SEAR) was conducted during the summer of 2000 at the Bachman Road site in Oscoda, MI. Part two of this two-part paper describes results from partitioning and nonpartitioning tracer tests, SEAR operations, and post-treatment monitoring. For this field test, 68 400 L of an aqueous solution of 6% (wt) Tween 80 were injected to recover tetrachloroethene-nonaqueous phase liquid (PCE-DNAPL) from a shallow, unconfined aquifer. Results of a nonreactive tracer test, conducted prior to introducing the surfactant solution, demonstrate target zone sweep and hydraulic control, confirming design-phase model predictions. Partitioning tracer test results suggest PCE-DNAPL saturations of up to 0.74% within the pilot-scale treatment zone, consistent with soil core data collected during site characterization. Analyses of effluent samples taken from the extraction well during SEAR operations indicate that a total of 19 L of PCE and 95% of the injected surfactant were recovered. Post-treatment monitoring indicated that PCE concentrations at many locations within the treated zone were reduced by as much as 2 orders of magnitude from pre-SEAR levels and had not rebounded 450 days after SEAR operations ceased. Pilot-scale costs ($365 900) compare favorably with design-phase cost estimates, with approximately 10% of total costs attributable to the intense sampling density and frequency. Results of this pilot-scale test indicate that careful design and implementation of SEAR can result in effective DNAPL mass removal and a substantial reduction in aqueous concentrations within the treated source zone under favorable geologic conditions
    Environmental Science and Technology 04/2005; 39(6):1791-801. · 5.26 Impact Factor
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    ABSTRACT: Alcohol addition has been suggested for use in combination with surfactant flushing to enhance solubilization kinetics and permit density control of dense non-aqueous phase liquid (DNAPL)-laden surfactant plumes. This study examined the effects of adding ethanol (EtOH) to a 4% Tween 80 (polyoxyethylene (20) sorbitan monooleate) solution used to flush tetrachloroethene (PCE)-contaminated porous media. The influence of EtOH concentration, subsurface layering and scale on flushing solution delivery and PCE recovery was investigated through a combination of experimental and mathematical modeling studies. Results of batch experiments demonstrated that the addition of 2.5%, 5% and 10% (wt.) EtOH incrementally increased the PCE solubilization capacity and viscosity of the surfactant solution, while reducing solution density from 1.002 to 0.986 g/cm3. Effluent concentration data obtained from one-dimensional (1-D) column experiments were used to characterize rate-limited micellar solubilization of residual PCE, which was strongly dependent upon flow velocity and weakly dependent upon EtOH concentration. Two-dimensional (2-D) box studies illustrated that minor differences (0.008 g/cm3) between flushing and resident solution density can strongly influence surfactant front propagation. A two-dimensional multiphase simulator, MISER, was used to model the influence of EtOH composition on the aqueous flow field and PCE mass recovery. The ability of the numerical simulator to predict effluent concentrations and front propagation was demonstrated for both 1-D columns and 2-D boxes flushed with EtOH-amended Tween 80 solutions. Results of this study quantify the potential influence of alcohol addition on surfactant solution properties and solubilization capacity, and demonstrate the importance of considering small density variations in remedial design.
    Journal of Contaminant Hydrology 04/2004; 69(1-2):73-99. · 2.89 Impact Factor
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    ABSTRACT: Two-dimensional multiphase flow and transport simulators were refined and used to numerically investigate the entrapment and dissolution behavior of tetrachloroethylene (PCE) in heterogeneous porous media containing spatial variations in wettability. Measured hydraulic properties, residual saturations, and dissolution parameters were employed in these simulations. Entrapment was quantified using experimentally verified hydraulic property and residual saturation models that account for hysteresis and wettability variations. The nonequilibrium dissolution of PCE was modeled using independent estimates of the film mass transfer coefficient and interfacial area for entrapped and continuous (PCE pools or films) saturations. Flow simulations demonstrate that the spatial distribution of PCE is highly dependent on subsurface wettability characteristics that create differences in PCE retention mechanisms and the presence of subsurface capillary barriers. For a given soil texture, the maximum and minimum PCE infiltration depth was obtained when the sand had intermediate (an organic-wet mass fraction of 25%) and strong (water- or organic-wet) wettability conditions, respectively. In heterogeneous systems, subsurface wettability variations were also found to enhance or diminish the performance of soil texture-induced capillary barriers. The dissolution behavior of PCE was found to depend on the soil wettability and the spatial PCE distribution. Shorter dissolution times tended to occur when PCE was distributed over large regions due to an increased access of flowing water to the PCE. In heterogeneous systems, capillary barriers that produced high PCE saturations tended to exhibit longer dissolution times.
    Journal of Contaminant Hydrology 01/2004; 67(1-4):133-57. · 2.89 Impact Factor
  • Journal of Environmental Engineering-asce - J ENVIRON ENG-ASCE. 01/2004; 130(11).
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    ABSTRACT: The ability of a multiphase flow model to capture the migration behavior of chlorinated solvents under conditions of surfactant-facilitated interfacial tension (IFT) reduction is assessed through comparison of model predictions with observations from controlled laboratory experiments. Tetrachloroethene (PCE) was released in two-dimensional saturated systems, packed with sandy media that incorporated rectangular lenses of capillary contrast. Spatially uniform interfacial tension conditions were created in the tanks by pre-flushing the porous medium with either Milli Q water or an aqueous surfactant solution. Experimental observations showed that surfactant-facilitated IFT reductions substantially lowered capillary resistance to the vertical downward migration of PCE and enabled PCE to enter finer grained, less permeable lenses that were not penetrated in the absence of surfactant. An immiscible flow model was used to simulate the conditions of the laboratory experiments. Under higher IFT conditions (47.5 and 5 dyn/cm), the model could successfully predict the general migration behavior of the organic liquid. Model predictions, however, exhibited poorer agreement with observed migration pathways under low IFT conditions (0.5 dyn/cm). In all cases, the predicted PCE distributions were influenced by selection of the parametric model for capillary retention and relative permeability. Simulated migration rates were more consistent with observed behavior when the Brooks-Corey/Burdine model was employed. For low interfacial tensions, improved predictions of migration pathways were obtained through grid refinement and incorporation of small-scale packing variability. Simulations highlight the substantial sensitivity of model predictions to the capillary pressure-scaling factor, grid resolution, and small-scale porosity variations at interfaces of permeability contrast under reduced IFT conditions.
    Journal of Contaminant Hydrology 08/2003; 64(3-4):227-52. · 2.89 Impact Factor
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    ABSTRACT: This paper provides an overview of the application of flow and transport simulators to the design and performance evaluation of a surfactant enhanced remediation pilot demonstration in Oscoda, Michigan, USA. For model simulations, input parameters were estimated from batch and column experiments conducted with aquifer materials and fluids collected from the site. Geostatistical methods were used, in conjunction with available grain size data from core samples, to generate representative hydraulic conductivity distributions for the unconfmed glacial outwash formation. The final remedial design incorporated a gallery of water injection wells, installed behind the surfactant injection points, to control surfactant delivery and maximize solubi-lized plume capture. Model predictions of test performance are compared with actual aqueous concentration measurements within the treated source zone. Discrepancies between predicted and measured concentrations are identified and discussed. Extraction well breakthrough data are also evaluated to explore the effectiveness of DNAPL removal and surfactant recovery.
    07/2001;
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    ABSTRACT: A numerical model of surfactant enhanced solubilization was developed and applied to the simulation of nonaqueous phase liquid recovery in two-dimensional heterogeneous laboratory sand tank systems. Model parameters were derived from independent, small-scale, batch and column experiments. These parameters included viscosity, density, solubilization capacity, surfactant sorption, interfacial tension, permeability, capillary retention functions, and interphase mass transfer correlations. Model predictive capability was assessed for the evaluation of the micellar solubilization of tetrachloroethylene (PCE) in the two-dimensional systems. Predicted effluent concentrations and mass recovery agreed reasonably well with measured values. Accurate prediction of enhanced solubilization behavior in the sand tanks was found to require the incorporation of pore-scale, system-dependent, interphase mass transfer limitations, including an explicit representation of specific interfacial contact area. Predicted effluent concentrations and mass recovery were also found to depend strongly upon the initial NAPL entrapment configuration. Numerical results collectively indicate that enhanced solubilization processes in heterogeneous, laboratory sand tank systems can be successfully simulated using independently measured soil parameters and column-measured mass transfer coefficients, provided that permeability and NAPL distributions are accurately known. This implies that the accuracy of model predictions at the field scale will be constrained by our ability to quantify soil heterogeneity and NAPL distribution.
    Journal of Contaminant Hydrology 05/2001; · 2.89 Impact Factor
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    ABSTRACT: This presentation provides an overview of the design and performance evaluation of a surfactant enhanced remediation pilot demonstration conducted in the summer of 2000 at a former dry cleaning facility in Oscoda, Michigan, USA. The unconfined contaminated formation is composed of relatively homogeneous glacial outwash sands, underlain by a thick clay layer. Core samples have revealed the presence of a reasonably persistent coarse sand and gravel layer at a depth of 11-16 feet and a sand/silt/clay transition zone at the base of the aquifer. A narrow tetrachloroethylene (PCE) plume emanates from the suspected source area, beneath the former dry cleaning building, and discharges into Lake Huron, approximately 700 feet down gradient. There is little evidence of microbial plume attenuation at the site. Aqueous samples from multilevel piezometers installed beneath the building have confirmed the presence of residual PCE within the coarse sand and gravel layer and have detected consistently high PCE concentrations at the base of the aquifer. The actual distribution and volume of entrapped PCE, however, is unknown. A surfactant injection and recovery scheme was designed and implemented to effectively flush the identified source area beneath the building. In this scheme, a line of water injection wells was installed behind the surfactant injection points to control surfactant delivery and maximize solubilized plume capture. Prior to surfactant injection, conservative and partitioning tracer tests were also conducted to confirm sweep and estimate source zone mass. Mass recovery calculations indicate that more than 94% of the injected surfactant and approximately 19 liters of PCE were recovered during the test. This volume of DNAPL is consistent with estimated low saturations within the swept zone. Single and multiphase transport models were employed to aid in remedial design and predict system performance. For the model simulations, input parameters were determined from batch and column experiments conducted with aquifer materials and fluids collected from the site. Model hydraulic conductivity distributions were generated using geostatistical methods, in conjunction with available grain size data from core samples. Model predictions of surfactant breakthrough and PCE solubilization are compared to measurements from the multilevel sampling points within the source zone. Discrepancies between predicted and actual test performance are identified and discussed.
    AGU Spring Meeting Abstracts. 05/2001;
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    Klaus M. Rathfelder, John R. Lang, Linda M. Abriola
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    ABSTRACT: The efficiency and effectiveness of soil vapor extraction (SVE) and bioventing (BV) systems for remediation of unsaturated zone soils is controlled by a complex combination of physical, chemical and biological factors. The Michigan soil vapor extraction remediation (MISER) model, a two-dimensional numerical simulator, is developed to advance our ability to investigate the performance of field scale SVE and BV systems by integrating processes of multiphase flow, multicomponent compositional transport with nonequilibrium interphase mass transfer, and aerobic biodegradation. Subsequent to the model presentation, example simulations of single well SVE and BV systems are used to illustrate the interplay between physical, chemical and biological processes and their potential influence on remediation efficiency and the pathways of contaminant removal. Simulations of SVE reveal that removal efficiency is controlled primarily by the ability to engineer gas flow through regions of organic liquid contaminated soil and by interphase mass transfer limitations. Biodegradation is found to play a minor role in mass removal for the examined SVE scenarios. Simulations of BV systems suggest that the effective supply of oxygen may not be the sole criterion for efficient BV performance. The efficiency and contaminant removal pathways in these systems can be significantly influenced by interdependent dynamics involving biological growth factors, interphase mass transfer rates, and air injection rates. Simulation results emphasize the need for the continued refinement and validation of predictive interphase mass transfer models applicable under a variety of conditions and for the continued elucidation and quantification of microbial processes under unsaturated field conditions.
    Journal of Contaminant Hydrology 05/2000; · 2.89 Impact Factor
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    Scott A. Bradford, Linda M. Abriola, Klaus M. Rathfelder
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    ABSTRACT: The migration and entrapment of dense nonaqueous phase liquids (DNAPLs) in aquifer formations is typically believed to be controlled by physical heterogeneities. This belief is based upon the assumption that permeability and capillary properties are determined by the soil texture. Capillarity and relative permeability, however, will also depend on porous medium wettability characteristics. This wettability may vary spatially in a formation due to variations in aqueous phase chemistry, contaminant aging, and/or variations in mineralogy and organic matter distributions. In this work, a two-dimensional multiphase flow simulator is modified to simulate coupled physical and chemical formation heterogeneity. To model physical heterogeneity, a spatially correlated permeability field is generated, and then related to the capillary pressure-saturation function according to Leverett scaling. Spatial variability of porous medium wettability is assumed to be correlated with the natural logarithm of the intrinsic permeability. The influence of wettability on the hysteretic hydraulic property relations is also modeled. The simulator is then employed to investigate the potential influence of coupled physical and chemical heterogeneity on DNAPL flow and entrapment. For reasonable ranges of wettability characteristics, simulations demonstrate that spatial variations in wettability can have a dramatic impact on DNAPL distributions. Higher organic saturations, increased lateral spreading, and decreased depth of infiltration were predicted when the contact angle was varied spatially. When chemical heterogeneity was defined by spatial variation of organic-wet solid fractions (fractional wettability porous media), however, the resultant organic saturation distributions were more similar to those for perfectly water-wet media, due to saturation dependent wettability effects on the hydraulic property relations.
    Advances in Water Resources. 01/1999;
  • Klaus Rathfelder, Linda M. Abriola
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    ABSTRACT: Numerical experiments are performed to explore the influence of model assumptions and parameters on the prediction of two-phase flow during long-term NAPL redistribution. Sensitivity of numerical solutions to grid resolution and the use of alternative fitting functions for capillary retention data are examined. Due to the inclusion of capillary entrapment, numerical solutions in one- and two-dimensions are strongly dependent on grid resolution. Solution convergence tests based upon spreading behavior reveal that nodal spacings as small as one-fifth to one-tenth of the displacement pressure head may be required to obtain reasonable convergence in some simulations. Solutions employing the Brooks and Corey and van Genuchten functional forms are found to yield different solution behavior. These differences are attributed to the representation of capillary pressure below the entry pressure. Brooks and Corey solutions exhibited greater spreading, less inclination to penetrate semi-permeable layers, and poorer spatial convergence behavior.
    Advances in Water Resources 03/1998; · 2.41 Impact Factor
  • S.A. Bradford, L.M. Abriola, K.M. Rathfelder
    Advances in Water Resources 01/1998; 22(2). · 2.41 Impact Factor
  • Hillel Rubin, Klaus Rathfelder, Linda M. Abriola
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    ABSTRACT: This work explores the rate-limited dissolution of entrapped nonaqueous phase liquids (NAPLs) in a fractured ``permeable`` formation through the use of mathematical models, developed on the basis of a simple conceptual framework. The feasibility of pump-and-treat operations in such formations is assessed through characterization of dimensionless system parameters governing NAPL dissolution and solute transport. These dimensionless parameters include the ratio of permeable block to fracture flow (mobility number), the system dimensionless mass transfer coefficient, and the number of contaminated fracture sections. A closed form analytical solution is developed for the simple case of a single contaminated fracture section. For domains with a large number of contaminated fracture sections, a numerical approach is presented that combines a finite difference scheme for simulation of solute transport in the fracture network together with an analytical solution for solute transport in the permeable block flow. The most favorable conditions for pump-and-treat systems are shown to be systems with large mobility numbers and large mass transfer coefficients. In systems with intermediate and small values of these parameters, effluent solute concentrations may be significantly below equilibrium values, reducing the effectiveness of pump-and-treat remediation. It is also shown that an equivalent continuum approach can be used to model rate-limited NAPL dissolution and transport in the simplified fractured permeable formation. The effective mass transfer coefficient for the representative continuum, however, is nonlinearly related to the local mass transfer coefficient.
    Journal of Environmental Engineering 01/1997; 123(3):204-216. · 1.40 Impact Factor
  • Klaus Rathfelder, Linda M. Abriola
    Water Resources Research 03/1996; 32(3):761-761. · 3.15 Impact Factor
  • Avery H. Demond, Klaus Rathfelder, Linda M. Abriola
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    ABSTRACT: Many numerical models which describe the movement of a separate organic liquid phase in the subsurface require information about the relationships between capillary pressure and saturation, and between relative permeability and saturation. An evaluation of the information available for these relationships suggests that substantial discrepancies may be introduced into simulations if estimated, rather than measured, data are employed. The purpose of this study was to quantify these deviations. Two-phase displacement simulations were performed in one and two dimensions for several organic liquid-water systems. Both constant-head and constant-flux boundary conditions were employed at a variety of flow rates and time scales, using both measurements and estimates of capillary pressure and relative permeability for a sandy aquifer material. The results demonstrate that the use of estimated transport relationships produces significantly different predictions of organic liquid migration. The magnitude of the deviations between predictions may be as high as 25% or more after relatively short displacement periods, depending on the boundary conditions of the simulated scenario, as well as on the physical characteristics of the two-phase system. For the systems examined, most of the deviations resulted from the estimates for relative permeability to the organic liquid. Thus, improved methods for the estimation of the relative permeability to the organic liquid are needed to reduce the uncertainty in displacement simulations.
    Journal of Contaminant Hydrology 01/1996; · 2.89 Impact Factor
  • K. Rathfelder, J. R. Lang, L. M. Abriola
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    ABSTRACT: Soil vapor extraction (SVE) has evolved over the past decade as an attractive in situ remediation method for unsaturated soils contaminated with volatile organic compounds (VOCs). SVE involves the generation of air flow through the pores of the contaminated soil to induce transfer of VOCs to the air stream. Air flow is established by pumping from vadose zone wells through which contaminant vapors are collected and transported above ground where they are treated, if required, and discharged to the atmosphere. The popularity of SVE technologies stems from their proven effectiveness for removing large quantities of VOCs from the soil, their cost competitiveness, and their relatively simple non-intrusive implementation. Widespread field application of SVE has occurred following the success of early laboratory and field scale feasibility studies [Texas Research Institute, 1980, 1984; Thornton and Wootan, 1982; Marley and Hoag, 1984; Crow et al., 1985, 1987]. As many as 18% of Superfund sites employ SVE remediation technologies [Travis and Macinnis, 1992] and numerous articles and reports have documented the application of SVE [e.g. Hutzler et al., 1989; Downey and Elliott, 1990; U.S. EPA, 1991; Sanderson et al, 1993; Gerbasi and Menoli, 1994; McCann et al., 1994;].
    Reviews of Geophysics 01/1995; 33:1067-1081. · 13.91 Impact Factor
  • Klaus Rathfelder, Linda M. Abriola
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    ABSTRACT: Numerical procedures for efficient mass conservative solutions of the head-based form of the Richards equation are presented. Mass conservative solutions are shown to result when the capacity coefficient, C, is formulated by equating the storage term and its chain rule expansion in their discretized forms. Equivalence in the storage term expansion is maintained in finite difference models when C is evaluated with a standard chord slope approximation. This scheme is shown to produce excellent global mass balance accuracy in simulations of vertical moisture infiltration. An analogous approach to the expansion of the storage term using finite elements results in element dependent expressions of C. Application of this approach produces mass balance accuracy with errors less than 1%, but also exhibits slow convergence in the consistent form. A nontraditional finite element procedure is presented which maintains equivalence in the storage term expansion when C is evaluated with the standard chord slope approximation. This scheme exhibits excellent mass balance accuracy, in either the consistent or lumped forms, without significant loss in computational efficiency.
    Water Resources Research - WATER RESOUR RES. 01/1994; 30(9):2579-2586.
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    Linda M. Abriola, Klaus Rathfelder
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    ABSTRACT: Mass balance accuracy of two-phase immiscible flow models used for contaminant hydrology applications is examined through comparisons of finite element and finite difference solutions of the pressure-based and pressure-saturation formulations. The influence of model formulation and initial conditions on mass balance performance is explored. Model simulations demonstrate that accurate solutions for multiphase flow problems can be obtained with either finite element or finite difference, pressure-based or pressure-saturation formulations, if coefficients and initial conditions are properly treated. In the pressure-based formulation, capacity coefficients arise from the expansion of the saturation variables in terms of capillary pressure. Mass balance accuracy depends upon the proper evaluation of the capacity coefficients when the capillary pressure—saturation relation is nonlinear. Capacity coefficient approximations for finite element pressure-based models are developed which preserve elemental expansion of the saturation derivative. These approximations are shown to produce good mass balance results and accurate solutions, in contrast with traditional finite element approaches. When the organic liquid is initially absent from a domain, simulations reveal that mass balance accuracy is obtained only when the initial pressure distribution is established from a zero capillary pressure condition. The influence of matrix mass lumping and the minimum value of the capacity coefficient on model performance is also investigated.
    Advances in Water Resources 01/1993; · 2.41 Impact Factor

Publication Stats

338 Citations
56.40 Total Impact Points

Institutions

  • 2005
    • Tufts University
      • Department of Civil and Environmental Engineering
      Medford, MA, United States
  • 2004
    • Los Alamos National Laboratory
      • Chemistry Division
      Los Alamos, NM, United States
    • Agricultural Research Service
      Kerrville, Texas, United States
  • 1993–2001
    • University of Michigan
      • Department of Civil and Environmental Engineering
      Ann Arbor, MI, United States