Surfactant Enhanced DNAPL Source Zone Remediation: Results of a Field Demonstration and Implications for Bioavailability

This presentation provides an overview of the design and performance evaluation of a surfactant enhanced remediation pilot-scale demonstration conducted in the summer of 2000 at a former dry cleaning facility in Oscoda, Michigan. The Bachman Road Site is underlain by an unconfined aquifer, composed of relatively homogeneous glacial outwash sands. This formation is confined below by a thick clay layer. A narrow tetrachloroethylene (PCE) plume emanates from the suspected source area, discharging into Lake Huron, approximately 700 feet down gradient. Prior to the test, there was little evidence of microbial plume attenuation at the site and concentrations of PCE were known to exceed 10 mg/L in portions of the soluble plume. Subsequent drive point and core sampling confirmed even higher PCE concentrations beneath the former dry cleaning building, consistent with the presence of residual PCE. The actual distribution and volume of entrapped PCE, however, was unknown.

A surfactant injection and recovery scheme was designed and implemented to effectively flush the identified source area beneath the building. The selected nonionic surfactant, Tween 80, was chosen for its biodegradability and potential to enhance the aqueous solubility of PCE by two to three orders of magnitude. Single and multiphase transport models were employed to aid in remedial design and predict system performance. Prior to surfactant injection, conservative and partitioning tracer tests were conducted to confirm sweep and estimate source zone mass. Measurements conducted during the test confirmed excellent surfactant and PCE mass recovery. The capabilities and limitations of this source zone remediation technology are highlighted, emphasizing the potential implications for contaminant mass flux reduction and contaminant plume attenuation. Results of subsequent source zone monitoring at the site are also presented that provide evidence of stimulation of microbial activity and chlorinated solvent transformation within the swept zone.