Controlling transport processes during NAPL removal by soil venting

Soil venting is a widely used technique to remediate unsaturated soils contaminated with organic contaminants. A fundamental concern in the remedial design is to predict the performance of the venting system in terms of the contaminant vapor removal rates and the clean-up limits that can be achieved at a site. In this paper, a mass transport model to simulate the evaporation of nonaqueous phase contaminants from the unsaturated soil during venting is presented. In particular, the dependence of NAPL evaporation on the resistance due to diffusional transport within the liquid phase is discussed in detail. Various limiting mechanisms that control the contaminant removal from NAPL phase have been identified. Results from numerical simulations have indicated that interfacial concentration can be overpredicted by models employing complete mixing assumption when the mass transfer coefficients are high and the interface transfer rates are limited by the diffusional transport within the liquid layer. Venting scenarios were simulated using a multi-component numerical model in which diffusional resistance in the liquid layer was included. The predicted vapor concentrations in the outlet air have been found to be in good comparison with experimental data. Copyright (C) 1996 Elsevier Science Ltd