Use of Rebound Testing for Evaluation of Soil Vapor Extraction Performance at the Savannah River Site

Abstract In 1999, a pilot soil vapor extraction (SVE) system was installed at a waste area within the Department of Energy's Savannah River Site located near Aiken, South Carolina, to remediate trichloroethylene (TCE) contamination and to evaluate monitoring and operational strategies for SVE application in layered heterogeneous materials. The specific objectives of the results reported here were (1) to evaluate the use of rebound analysis of soil gas concentrations as the basis for operational strategies, and (2) establish the endpoint criteria for active remedial action. Three soil gas TCE concentration rebound tests were conducted over a period of 18 months to assess system performance and progress. For each rebound test, the system was shut down and allowed to equilibrate for two to four weeks. Soil gas TCE concentrations were measured several times during this equilibration period. Comparison of these rebound test results has been used for evaluating SVE system performance. A transient two‐dimensional diffusion model has been used to convert soil gas TCE rebound concentrations to estimates from distance to source, and the model predictions correspond with observed dense nonaqueous phase liquid at the site. Also, these rebound tests can provide sufficient information about contaminant distribution and SVE mass transfer limitations to select a reasonable and appropriate endpoint for active remedial operations.