At a former industrial site, the manufacturing buildings were removed in the 1990s, and a trichloroethylene (TCE) plume was discovered under one of the newly redeveloped buildings. Because two aging air-sparge remediation systems were expensive to operate and maintain, were not reducing source mass, and were not addressing potential vapor intrusion concerns, the responsible party hired Barr to conduct a remedial investigation and evaluate options for reducing the contamination.
Barr performed a subsurface investigation of one of the source areas, which was located under an existing building. We delineated a treatment zone and provided the necessary data for designing a remedy that would address movement of the source mass from under the building. We performed high-resolution characterization using membrane-interface/hydraulic profiling tool (MiHPT) boring and confirmed the results with soil samples and chemical and hydraulic analyses. Monitoring wells were installed to assess baseline geochemical conditions and contaminant concentrations in the groundwater.
We designed a “biobarrier” remedy with a multi-mechanism approach to reduce contaminant movement. The design included injection of four amendments—an adsorption mechanism, an abiotic mechanism, and a dual-amendment biological mechanism—and verification of proper distribution of the amendments using soil borings and piezometers in the vicinity of the injection locations.
Results indicate the biobarrier performed as designed. Movement of TCE to the primary well downgradient of the biobarrier was reduced by up to 99.5 percent. Lessons learned from the biobarrier implementation were applied to a second source area at the site, which included extending the original biobarrier as well as applying the multi-mechanism remedy to the second source area. Performance monitoring is ongoing and indicates the source area remedy and extended biobarrier are reducing contaminant mass in and downgradient of the second source area.