Gas Permeability and Diffusivity in Undisturbed Soil: SVE Implications

Abstract

Accurate prediction of air transport parameters in variably saturated soil is a prerequisite for realistic modeling of soil vapor extraction (SVE) systems for cleanup of contaminated soil sites. Improved models for estimating gas diffusivity and gas permeability in undisturbed sandy and loamy soils from soil total porosity, air-filled porosity, and soil-water retention properties were developed based on gas diffusivity and permeability data from the literature representing more than 3,500 undisturbed soil core samples. The new models gave significant improvements in prediction accuracy compared with existing gas diffusivity and permeability models. The new models provide good predictions of gas diffusivity and permeability from other soil parameters that are easier to measure. The models therefore seem promising for reducing expenses associated with measurements of field parameters during preliminary remedial investigations at contaminated sites. The new predictive models were used in a two-dimensional numerical transport code for simulating SVE in trichloroethylene contaminated soil to evaluate the impact of air-filled porosity on SVE efficiency. Results imply that stochastic variations in air-filled porosity cause increased contaminant removal rates in the early stages of the SVE process.