The studies of Non-Aqueous Phase Liquid contaminants in groundwater are conducted in three stages: 1). Researches on the behavior of groundwater in saturated-unsaturated soils; 2) Researches on the transport mechanism of water-NAPL two-phase fluid contaminants in groundwater; 3) Researches on the migration mechanism of water-NAPL-gas (mainly gaseous NAPL) three-phase flow contaminants into subsurface including vadose zone. In this paper, the analysis is mainly concentrated on the second stage: the development of a comprehensive numerical method for simulating transport of two-phase flow in porous media and its corresponding finite element method source-code program. The fundamental theory and numerical discretization formulations are elaborated. The numerical difficulty brought about by the distinct non-linearity of the temporal evolution of saturation-dependent variables is overcome by the mixed-form formulation. Finally, two computational examples are given for verifying the correctness and demonstrating the preliminary applicability. In addition, the function of two-phase immiscible flow, especially in FLAC is used to simulate the same examples and the results are compared to further verify the correctness of the numerical development.

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