A VERTICAL EQUILIBRIUM-MODEL FOR ASSESSING NONAQUEOUS PHASE LIQUID CONTAMINATION AND REMEDIATION OF GROUNDWATER SYSTEMS

A numerical model has been developed to provide areal analyses of the three-dimensional spreading of immiscible liquids in groundwater syste ms. The model is intended for specific use in prediction of hydrocarbo n spreading from subsurface leaks and spills and in design and perform ance evaluation of remedial schemes. The mathematical formulation is b ased on vertical integration of the three-dimensional two-phase flow e quations and incorporation of the concept of gravity-capillary vertica l equilibrium (GCVE) in which a vertical balance of gravitational and capillary forces is assumed. History-dependent pseudo functions of cap illary pressure and relative permeabilities are introduced for the pre sent GCVE model. A direct numerical procedure for evaluating the pseud o functions is derived and verified using an example given in the petr oleum literature. An overview of numerical techniques for solving the nonlinear governing equations is presented. Special schemes for handli ng production wells are derived. Simulation examples are provided to v erify, validate, and demonstrate utility of the model. Numerical resul ts obtained from the GCVE model are compared with analytical and rigor ous multiphase three-dimensional numerical solutions. The model is fur ther validated using data from a laboratory investigation on waterfloo d, five-spot well performance. The results of these comparisons show t he validity of the GCVE modeling assumptions and accuracy and robustne ss of the proposed formulations and computational schemes. The numeric al study also indicates that the present model is highly efficient and suitable for field simulations on personal computers or workstations.