Multiphase Flow Model for NAPL Infiltration in Both the Unsaturated and Saturated Zones

Abstract

Soil pollution by organic matter is traditionally modeled through macroscale multiphase flow models, which rely on extensions of Darcy’s law and empirical relationships. The transfers between phases can be expressed by the phase equilibrium or by a kinetic model. In this study, initially, a two-phase model (air-water) is constructed to model water drainage from a two-dimensional (2D) geometry. Results from this are compared with experimental results from literature. In addition, a three-phase flow model was created and applied for the simulation of the infiltration of nonaqueous phase liquid (NAPL) through the unsaturated, capillary, and saturated zones. Again, simulation results are compared with experimental results both from tests performed in this study and from literature. These are 2D NAPL infiltration experiments in sand packs, in which toluene and Soltrol, respectively, are infiltrated in both the unsaturated and saturated zones. Comparisons were made based on visual observation of the outline of the progressing NAPL front and the water saturation data. A two-phase model for the drainage step through a 2D cell was first used to deduce the initial conditions of the soil. Subsequently, a three-phase model was created that can predict the water saturation and NAPL pressure within the 2D cell and reproduce the pollutant infiltration through the unsaturated, capillary, and saturated zones. Results show the effect of the capillary nature of soil on the vertical and lateral plume spread.