Three-Dimensional Modeling of Contaminants Transport in Subsurface Environment: From the Land Surface Through the Unsaturated Zone and Fully Saturated Aquifers

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9317009 Yeh The importance of field heterogeneities in groundwater pollution problems has been widely recognized during the last decade. Many field and theoretical studies have been conducted to enhance our understanding of their impacts and to improve our predictive ability of contaminant migration in the field. Conditional simulation is generally accepted as the most logical approach that can improve our prediction of contaminant transport in the field. Many studies are, however, adopt simplified and unrealistic scenarios such as one or two-dimensional steady-state flow. Studies have never been conducted where contaminants move multi- dimensionally through the unsaturated zone to the water table and propagate through the aquifer. One of the limiting factors is computational difficulty and the enormous amount of CPU time required for multi-dimensional numerical simulation. This problem is most severe in the case of flow and transport in the unsaturated zone due to the nonlinearity of the governing flow equation. Stochastic conditional simulations are even more formidable. An approach recently developed by the investigator reduces the CPU time for simulating transport of solutes in two-dimensional unsaturated heterogeneous soils by two or three orders of magnitude. This technical breakthrough allows conditional simulation of solute transport in heterogeneous porous media under unsaturated conditions. The robustness of the approach compels us to try it on three-dimensional transport of contaminants from heterogeneous unsaturated vadose zones to fully saturated aquifers. The overall objectives of the study are to develop a computationally feasible algorithm for simulation of contaminant transport in three-dimensional heterogeneous porous media under variably saturated conditions and to investigate the potential of our proposed conditional concept for designing sampling procedures that improves our prediction of contaminant migration in subsurface envir onment. In other words, we would like to assess the degree of sampling is necessary to predict migration of contaminants in the subsurface environment.