Soil and groundwater at the former Feley Farms Site (Michigan, USA) was impacted by gasoline constituents that originated from former USTs. The leaking tanks were removed in 1995; based on the reported petroleum-contaminated water seeping into the excavation hole along the surface of the bedrock during the tank removal process, groundwater monitoring was recommended.
The results of the 1996-97 monitoring effort showed that groundwater had been impacted at the source of the gasoline tank leak, which was located between the farmhouse and the farm water well. Benzene levels and those of other gasoline-associated pollutants substantially exceeded Michigan standards. Due to the danger of the gasoline leaking into the farm water supply, USDA contracted with The Paz Group for additional services to delineate, monitor and remediate the contaminants. Accordingly, a soil vapor extraction system operated for 96 months followed by a groundwater pump-and-treat system (November 2000). A drop in remedial performance of the pumping system was encountered hence, in October, 2006 EHC-O was used to remove residual benzene and other constituents from an average concentration of 50 ug/L (ppb) to below their regulatory limits (MCLs of 5 ppb). EHC-O was the preferred source of slow-release oxygen due to its ability to supply oxygen plus inorganic nutrients and buffering capacity in a more cost effective manner. Within 6 months of EHC-O treatment, benzene concentrations were reduced by 99%, below the State of Michigan standards. Post-treatment monitoring showed no re-bound > 1 year post EHC-O application, with all monitored constituents being below the analytical detection limits. This timely and cost-effective remedial action facilitated a clean closure and freedom for future property transfer. The EHC-O product cost was < US$0.20/ft3 (US$18/m3).