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An economic decision framework using modeling for improving aquifer remediation design

Description: Reducing cost is a critical challenge facing environmental remediation today. One of the most effective ways of reducing costs is to improve decision-making. This can range from choosing more cost- effective remediation alternatives (for example, determining whether a groundwater contamination plume should be remediated or not) to improving data collection (for example, determining when data collection should stoop). Uncertainty in site conditions presents a major challenge for effective decision-making. We present a framework for increasing the effectiveness of remedial design decision-making at groundwater contamination sites where there is uncertainty in many parameters that affect remediation design. The objective is to provide an easy-to-use economic framework for making remediation decisions. The presented framework is used to 1) select the best remedial design from a suite of possible ones, 2) estimate if additional data collection is cost-effective, and 3) determine the most important parameters to be sampled. The framework is developed by combining elements from Latin-Hypercube simulation of contaminant transport, economic risk-cost-benefit analysis, and Regional Sensitivity Analysis (RSA).
Date: November 1, 1995
Creator: James, B.R.; Gwo, J.P. & Toran, L.E.
Partner: UNT Libraries Government Documents Department

Murt user`s guide: A hybrid Lagrangian-Eulerian finite element model of multiple-pore-region solute transport through subsurface media

Description: Matrix diffusion, a diffusive mass transfer process,in the structured soils and geologic units at ORNL, is believe to be an important subsurface mass transfer mechanism; it may affect off-site movement of radioactive wastes and remediation of waste disposal sites by locally exchanging wastes between soil/rock matrix and macropores/fractures. Advective mass transfer also contributes to waste movement but is largely neglected by researchers. This report presents the first documented 2-D multiregion solute transport code (MURT) that incorporates not only diffusive but also advective mass transfer and can be applied to heterogeneous porous media under transient flow conditions. In this report, theoretical background is reviewed and the derivation of multiregion solute transport equations is presented. Similar to MURF (Gwo et al. 1994), a multiregion subsurface flow code, multiplepore domains as suggested by previous investigators (eg, Wilson and Luxmoore 1988) can be implemented in MURT. Transient or steady-state flow fields of the pore domains can be either calculated by MURF or by modelers. The mass transfer process is briefly discussed through a three-pore-region multiregion solute transport mechanism. Mass transfer equations that describe mass flux across pore region interfaces are also presented and parameters needed to calculate mass transfer coefficients detailed. Three applications of MURT (tracer injection problem, sensitivity analysis of advective and diffusive mass transfer, hillslope ponding infiltration and secondary source problem) were simulated and results discussed. Program structure of MURT and functions of MURT subroutiness are discussed so that users can adapt the code; guides for input data preparation are provided in appendices.
Date: April 1, 1995
Creator: Gwo, J.P.; Jardine, P.M.; Yeh, G.T. & Wilson, G.V.
Partner: UNT Libraries Government Documents Department

Modeling small-scale physical non-equilibrium and large-scale preferential fluid and solute transport in a structured soil

Description: The deviation of non-reactive solute transport from that predicted by classical convection-dispersion equations is usually attributed to physical non-equilibrium caused by small- and large-scale pore structures in porous media. Diffusion of fluid and solute into micropores or rock matrix may occur locally, while fluid and solutes can also be channeled preferentially through interconnected macropores or fractures. A multiple-pore-region (MPR) approach with local advective-diffusive mass exchange is adopted to simulate soil column tracer breakthrough and field-scale tracer releases in the Melton Branch Subsurface Transport Facility within the Oak Ridge Reservation, Tennessee. The soil column simulation indicates that both inter-region mass exchange and intra-region convection-dispersion contribute to small-scale solute transport in approximately the same order of magnitude. The field-scale study suggests that advective mass exchange has minor effect on subsurface hydrographs, and that large diffusive mass exchange may retain tracers near the source area. Comparison of modeling results and field data suggests that subsurface bedding planes on the field site may be the cause of large-scale heterogeneity and preferential mass transport.
Date: September 1, 1994
Creator: Gwo, J. P.; Jardine, P. M.; Wilson, G. V. & Yeh, G.-T.
Partner: UNT Libraries Government Documents Department

Modeling subsurface contaminant reactions and transport at the watershed scale

Description: The objectives of this research are: (1) to numerically examine the multiscale effects of physical and chemical mass transfer processes on watershed scale, variably saturated subsurface contaminant transport, and (2) to conduct numerical simulations on watershed scale reactive solute transport and evaluate their implications to uncertainty characterization and cost benefit analysis. Concurrent physical and chemical nonequilibrium caused by inter aggregate gradients of pressure head and solute concentration and intra-aggregate geochemical and microbiological processes, respectively, may arise at various scales and flowpaths. To this date, experimental investigations of these complex processes at watershed scale remain a challenge and numerical studies are often needed for guidance of water resources management and decision making. This research integrates the knowledge bases developed during previous experimental and numerical investigations at a proposed waste disposal site at the Oak Ridge National Laboratory to study the concurrent effects of physical and chemical nonequilibrium. Comparison of numerical results with field data indicates that: (1) multiregion, preferential flow and solute transport exist under partially saturated condition and can be confirmed theoretically, and that (2) mass transfer between pore regions is an important process influencing contaminant movement in the subsurface. Simulations of watershed scale, multi species reactive solute transport suggest that dominance of geochemistry and hydrodynamics may occur simultaneously at different locales and influence the movement of one species relative to another. Execution times on the simulations of the reactive solute transport model also indicate that the model is ready to assist the selection of important parameters for site characterization.
Date: December 1997
Creator: Gwo, J. P.; Jardine, P. M.; D`Azevedo, E. F. & Wilson, G. V.
Partner: UNT Libraries Government Documents Department

HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media

Description: The computer program HYDROBIOGEOCHEM is a coupled model of HYDROlogic transport and BIOGEOCHEMical kinetic and/or equilibrium reactions in saturated/unsaturated media. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed biogeochemical reactions. The transport equations are solved for all aqueous chemical components and kinetically controlled aqueous species. HYDROBIOGEOCHEM is designed for generic application to reactive transport problems affected by both microbiological and geochemical reactions in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical and microbial reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical and microbial concentrations as a function of time and space, and the chemical speciation at user-specified nodes.
Date: July 1, 1998
Creator: Yeh, G.T.; Salvage, K.M.; Gwo, J.P.; Zachara, J.M. & Szecsody, J.E.
Partner: UNT Libraries Government Documents Department