Biological and Geochemical Groundwater Treatment Using Recirculation for Distribution to Prevent Excavation

APTIM Authors/Contributors

Background/Objectives

At the former Naval Air Station Moffett Field California Traffic Island Area past dry-cleaning operations and the discharging of chemicals into a compromised sanitary sewer line led to elevated levels of tetrachloroethene (PCE) in the subsurface. Groundwater investigations at this site have determined that DNAPL levels of chlorinated ethenes may be present on the south side of the Traffic Circle, and in 2020 PCE was detected at 140,000 µg/L. Previous treatability studies evaluated the effectiveness of anaerobic and abiotic technologies to reduce contamination. In 2015 a combined biotic and abiotic approach using a solid phase iron was implemented. Reductions in chlorinated ethenes were observed where amendments were in place. However, during the implementation, high pressure injections were conducted in which surfacing and distribution issues were observed. Also, the tight spacing required for this type of injection was difficult in areas where multiple utilities were present. To reduce the contaminant levels in the groundwater at the Traffic Island Area excavations of the vadose zone and soils in the shallow groundwater have been considered. However, due to the challenges created by utilities, depth of impact, concentrations of COC present, and the need to limit the impact to traffic, a recirculation application of enhanced anaerobic bioremediation / in situ chemical reduction using dissolved ferrous iron as the source removal action was conducted in lieu of shallow soil excavation.

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