Evaluation of soil vapor extraction performance for trichloroethylene (TCE) remediation in layered heterogeneous soils

Soil vapor extraction (SVE) is a commonly-used in situ method for the remediation of volatile organic contamination in the vadose zone. In SVE, wells are screened in the subsurface according to subsurface geological features and contaminant distribution. Vacuum is applied to the configuration to draw the contaminant vapors to the surface for treatment and release. Development of accurate models to simulate the SVE process in the subsurface is essential to understanding its capabilities and predicting reasonable and achievable endpoints for its applications. Many modeling studies assume local equilibrium and linear partitioning in a homogenous subsurface. These assumptions do not account for the slow desorption and rebound that are observed during SVE in the field. More recently, researchers have begun to incorporate diffusion of contaminants from spherical soil aggregates into the overall SVE models to describe this behavior.; A pilot scale SVE system was installed at a small waste site in the Savannah River Site, to study the remediation of trichloroethylene (TCE) contamination in layered heterogeneous soils. The objectives of the work presented here were to develop a contaminant mass transfer model to simulate the SVE process in layered soils, using the conditions at this waste site as the basis for model development, and to use those predictions to evaluate the SVE system installed at this waste site.; The SVE model suggests that the inclusion of the aggregate component does not impact mass removal predictions in the presence of a non-aqueous phase liquid (NAPL) or high concentration vapor source; its effects are pronounced in the diffusion-only (rebound) stages. Subsurface soil gas TCE concentration rebound tests were conducted to assess system progress and performance during the course of operation. Application of the diffusion components of the overall model to this data resulted in predictions of the location a NAPL source that compared well to the location of an actual NAPL source that was discovered during the course of operation. The field data from the site coupled with the modeling results suggest strongly that four years of SVE operation at the waste site have removed the available TCE in the subsurface.