Soil vapor extraction performance in layered vadose zone materials

A pilot soil vapor extraction (SVE) system was installed at a small landfill within the Savannah River Site to address trichloroethylene ( TCE) contamination present in the vadose zone. The SVE system has been operating since September 1999 and numerous tests have been performed on the system. A model was developed to simulate SVE at this site, incorporating the effects of contaminant behavior in a layered subsurface as well as the effects of contaminant diffusion into and out of soil aggregates. The objectives of this study were to: (i) compare the fi eld data from the site with predictions from this mechanistic model; and ( ii) establish the case for closure based on fi eld observations and model predictions. A dense non-aqueous-phase liquid TCE source was discovered at the site during the course of operation. Location of this source compares well with the predicted residual source from the application of the diffusion components of the SVE model to soil gas TCE concentration rebound observations. Collectively, the fi eld observations and the model predictions strongly support the observations that a substantial portion of the source contamination at the site has been removed by the SVE system and that the criteria for site closure have been met.