Influence of spatial variability of soil properties on mass removal for a soil vapor extraction system

Abstract

A multiphase flow and transport model is modified and applied to study the influence of spatial variability of soil properties on predictions of contaminant mass removal for a soil vapor extraction system (SVES). Spatial distributions of mean particle size (d_m), soil porosity (ϕ), permeability (k) and interphase mass transfer rate between air and organic liquid phases (K_go) for nonuniform soil composed of fine‐ to coarse‐grain sands are considered in the model. For these parameters, <p and d_m are generated based on a geostatistical model and k and K_go are determined according to theoretical or empirical correlations expressed in terms of d_m and/or <p. Results show that uncertainty in spatial distribution of any of these parameters can exert a significant influence on the predicted removal percentage, even for cases with low variability in d_m . In particular, to rigorously predict SVES contaminant removal efficiency, one must assess in‐situ K_go value or the relationships of K_go to other factors. The present simulations show that uncertainty in spatial variation of these parameters can result in a wide variety of organic liquid saturation distributions during SVES operation, even if the predicted removal percentages are similar for different cases. For long‐term soil remediation by SVE, in order to promote SVES mass removal efficiency, intermediate stages of the operation must include reassessment of in‐situ contaminant mass distribution. This new information can be used to relocate extraction wells, if necessary, to promote SVES mass removal efficiency.

Key words:

• soil vapor extraction system
• nonequilbrium interphase mass transfer
• geostatistical model
• a multiphase flow and transport model

Notes

Corresponding author. (Tel: [phone] ext. 5218; Fax: [phone]; Email: [email protected])