Finite difference approach for mathematical simulation of soil vapor extraction from unsaturated zone

This paper describes the development of a mathematical model to simulate soil vapor extraction for the removal of gasoline-range hydrocarbons from the unsaturated zone. The model solves a set of partial differential equations for two-dimensional gas flow and advective-dispersive vapor transport in variably saturated porous media with a finite difference approach. The soil vapor extraction process involves volatilization, gas advection, gas diffusion, liquid diffusion, residual saturation, vapor-liquid equilibrium, and mass transfer. The variable mass transfer coefficient is governed by the diffusion process. Changes in the air permeability of the porous media are calculated as the residual liquids are volatilized. The model is intended for field-scale application to aid in design, development, and operation of high-efficiency soil vapor extraction systems.