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GBOMATRIX The site formerly contained two 12,000-gallon underground storage tanks (USTs), identified on ' a PHS/EHD inspection report as Tank#1 and Tank#4, both of which stored unleaded gasoline The tanks were removed on February 16, 1988 by Stockton Service Station Equip- ment Co , Inc (SSSE) Approximately 180 cubic yards of soil were excavated with the tanks to a depth of about 11 feet below ground surface (bgs) Presently, the area over the former tanks ' and excavation is covered with concrete and surrounded by industrial activities associated with the production, storage, and transport of liquid ammonia A survey of domestic, municipal, agricultural, industrial, and other supply wells within a 2,000-foot radius of the site was ' conducted No municipal or drinking water supply wells were identified within the 2,000-foot radius ' 1.2 HISTORY OF SITE WORK ' During removal of the USTs in 1988, discolored gray soil and strong petroleum product odors were detected at the southern ends of both tanks Minor petroleum product odor was detected ' at the north end of Tank#1, while no odor was detected at the north end of Tank#4 Four soil samples were collected by `California Water Labs' (CWL) near the ends of the USTs from a depth of approximately 13 feet bgs No groundwater was encountered during excavation or sampling Four additional soil samples were collected by CWL on March 15, 1988 These samples were collected from the same locations as during the tank pulls, but from a depth of 16 feet bgs A review of the PHS/EHD inspection report indicates that the inspector found "gray soil observed on all samples with petroleum-like odor " The report also notes that no groundwater was encountered to a depth of 16 feet bgs Soil samples collected from beneath the tanks were submitted to CWL for analysis All soil Isamples were analyzed for total petroleum hydrocarbons as gasoline (TPH-g) and total petroleum hydrocarbons as diesel (TPH-d) by EPA method 8020 Selected samples were ' analyzed for ethylene dibromide (EDB) by EPA method 8010, and total lead Analytical results indicated low levels of petroleum hydrocarbon compounds (PHCs) detected in the initial soil samples, primarily in the samples collected at the south ends of the tanks where petroleum product odor was detected However, PHC concentrations in the follow up samples collected approximately 5 feet below the initial samples, were significantly attenuated relative to the initial concentrations in the initial samples No EDB was detected in any of the samples Lead was detected at 6 to 12 4 milligrams per kilogram (mg/kg) in the initial samples from the north Iends of both tanks, but was not detected in the follow up samples at 16 feet bgs I IPROJECI`6437 000/6437 Wk PIn Site 3 doe 2