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EXPERIMENTAL EVALUATION OF TWO SHARP FRONT MODELS FOR VADOSE ZONE NON-AQUEOUS PHASE LIQUID TRANSPORT
Citation:
Illangasekare, T., D. Znidarcic, G. Walser, AND J W. Weaver*. EXPERIMENTAL EVALUATION OF TWO SHARP FRONT MODELS FOR VADOSE ZONE NON-AQUEOUS PHASE LIQUID TRANSPORT. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-94/197 (NTIS 95-178232), 1994.
Impact/Purpose:
Information.
Description:
Recent research efforts on the transport of immiscible organic wastes in subsurface the development of numerical models of various levels of sophistication. Systems have focused on the site characterization data needed to obtain. However, in real field applications, the model parameters are either difficult to obtain or are not easily available. As an alternative, a number of simple sharp front models which require relatively less data have been developed. Less rigorous data requirements and simplicity of use allows these types of models to be used as screening tools in risk assessment and remediation design. Laboratory experiments have been conducted to test two such models developed by the authors. Fundamental transport parameters for the media were determined using a flow-pump system. One-dimensional spill simulations of a non-aqueous phase liquid were conducted in vertical soil columns. Ponding depth and front location were traced visually. Dual-source gamma system was tested and then used to obtain saturation profiles of the water and oil phases. he profiles indicate the existence of a sharp front at the leading edge of the infiltrating oil phase. At the trailing end of the infiltrating oil, a gradual decline in saturation was observed. One of the models which is similar in concept to the Green-Ampt type infiltration models, assumes sharp leading and trailing fronts. It deviates from the experimental results for long modeling times. The second model based on kinematic wave formulation and the method of characteristics approximates the gradual decline in saturation behind the front and simulates the spill behavior well. Based on these experimental evaluations, the suitability and limitations of these simple models are determined. Simulated rainfall experiments have been conducted to observe extent of mobilization of the organic phase through water application. Water pushes the organic phase as a slug in front of the water phase (piston displacement). However, the water mobilizes nearly none of the organic phase below a phase content of 0.1. Two-dimensional experiments were conducted in a tank to test the applicability of the one-dimensional models to a two-dimensional situation. The saturation profiles were again determined using the dual-gamma system.