Modeling transient organic vapor transport in porous media with the dusty gas model

Abstract

The dusty gas model constitutive relationships were incorporated into a numerical model for three-phase, multicomponent flow and transport in porous media. The dusty gas model properly accounts for interactions between all gas-phase species in multicomponent gas mixtures. The model also included Knudsen diffusion, which becomes important in very fine grained soils. The dusty gas model results were compared to predictions based on Fick's law. For the cases studied, Fick's law overpredicted flux rates of organic compounds, the effect becoming more pronounced as the permeability of the soil and the Knudsen coefficient were reduced. Increasing moisture content also appeared to increase the difference between predictions based on the dusty gas model and those based on Fick's law. Hypothetical field-scale simulations were performed to show the impact of multicomponent effects and Knudsen diffusion in a sandy soil and in a clay soil. Results showed that remediation times were significantly underpredicted if Fick's law was used for gas-phase diffusion.