The Site is located in South San Francisco, California, and is currently used for rental car fleet parking and fueling. Impact to soil from gasoline and diesel fuel was detected during a UST removal and replacement in 2003. Investigations were conducted to characterize the magnitude and extent of petroleum hydrocarbon impact to soil at the Site which indicated that total petroleum hydrocarbons (TPH) as gasoline and diesel, and the fuel components benzene, toluene, ethylbenzene, xylenes (BTEX) and methyl-tert-butyl ether (MTBE), were present in soil at concentrations exceeding the Environmental Screening Levels (ESLs). Most of the impact was primarily limited to an approximate 15 foot diameter zone around the fuel dispensers. Tetra Tech selected use of an in situ chemical oxidation compound (ISCO) as the most feasible remedy for impacted soil at the Site. ISCO was injected into subsurface soil at the Site in three applications between July 2007 and March 2008. Baseline soil sampling was conducted prior to ISCO injection, and confirmation soil sampling was conducted following each ISCO injection event. Post injection BTEX and MTBE concentrations declined below the respective ESL values. In 2009, two sub-slab soil gas samples were collected from the fill material beneath the adjacent building. The soil gas samples were analyzed for TPH as gasoline and diesel, benzene, and MTBE. Analytical results indicate that TPH as gasoline and diesel were not detected at concentrations at or above the laboratory reporting limits. Benzene and MTBE were detected in sub-slab soil gas samples, but at concentrations below the respective soil gas ESL values. The Site has received preliminary closure.
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