A catastrophic release of approximately 2,323 gallons of unleaded gasoline occurred from a 6,000-gallon unleaded gasoline underground storage tank (UST). Interim remedial actions consisted of removal of UST and minimal contaminated soils, installation of a temporary light non-aqueous phase liquid (LNAPL) groundwater recovery system, vapor mitigation system for onsite indoor air, and carbon treatment for onsite supply well. Remedial actions included the removal of the entire UST system and excavation of all petroleum-impacted soils prior to installation of a new UST system. Site characterization activities consisted of the installation, development, and sampling of thirty-one (31) shallow monitoring wells to characterize the extent of offsite contamination.
An empirical fate and transport was prepared and approved by the Pennsylvania Department of Environmental Protection (DEP). Site-specific aquifer biodegradation electron acceptor values and aquifer test results were evaluated to determine; (1) the current size and location of the contaminant plume, (2) the historical size location of the contaminant plume including identifying the source area, (3) the future location of the contaminant plume and determination if steady-state conditions exist. Both primary and secondary lines of evidence were evaluated to demonstrate that biodegradation was occurring, and the natural attenuation rate was being artificially enhanced.
Monitored natural attenuation was the chosen groundwater remedial solution. Within 8 years, the contaminant concentrations were below the Statewide health standards.
A Site Characterization Report, Remedial Action Plan, and Remedial Action Completion Report were prepared and submitted to the DEP. The attainment of the residential, used aquifer, Statewide health standard was demonstrated in soil and groundwater. Liability relief was granted by the DEP.
