Demonstration of Surfactant-Enhanced Aquifer Remediation of Chlorinated Solvent DNAPL at Operable Unit 2, Hill AFB, Utah, Draft Final

During 1996 and 1997, five separate partitioning interwell tracer tests PITTs were conducted as part of two separate surfactant-enhanced aquifer remediation SEAR demonstrations targeting DNAPL primarily TCE at Operable Unit 2 OU2, Hill Air Force Base, Utah. These PITTs were used as a DNAPL characterization tool to accurately determine 1. the total aquifer volume swept 2. the total amount of DNAPL present in the swept aquifer volume and, 3. the average residual saturation present. PITTs were conducted before and after each SEAR demonstration to provide remediation performance assessments and were hydraulically controlled without using sheetpile walls. The successful implementation of field-scale PITTs required an engineering design strategy using conventional characterization activities, laboratory studies, and UTCHEM modeling. The volume sampled by each PITT was on the order of an average of 6500 cu ft 14,000 gallon pore volume. Tracer recoveries ranged from 79 to 92, indicating that, within experimental error, all of the injected tracers were recovered. The method of temporal moments was used to analyze each PITT, and the resulting DNAPL volume estimates were in close agreement with other measurements e.g. SEAR DNAPL recoveries and core data estimates. Thus, in sandy alluvium, PITTs are very accurate estimators of DNAPL volumes, and provide an excellent characterization and performance assessment tool for DNAPL remediation efforts. Based on the success of these PITTs, the USAF is currently conducting large-scale PITTs to characterize the entire DNAPL source zone at OU2.