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4.2 Groundwater Contamination The groundwater samples collected from the HydroPunch Ih locations and the monitoring wells indicate that the groundwater at the site has been impacted by petroleum hydrocarbons High levels of TPH-g and BTEX were detected In MW-1, MW-8, HP-1, HP-4, and HP-5 TPH-g and BTEX were not detected in the other ' HydroPunch I10 samples and groundwater monitoring wells Historically, BTEX and TPH-g constituents have been detected in MW-1 The results of the third quarter ' 1993 groundwater sampling correlate with these historical results Sufficient data have been collected to allow delineation of the approximate contaminant plume boundaries (Figure b) The source of the contamination appears to be the gasoline UST removed 1n 1987 This was the only UST that was observed to have leaked The elevated levels of TPH-g and BTEX detected 1n HP-4 and MW-8, the sample ' locations closest to the former UST, correlate with this conclusion The contaminant plume has migrated approximately 50 feet to MW-1 Based on the analytical results ' from HP-2, HP-3, and MW-9, the plume has not progressed much further than MW-1 ' Lead was not detected 1n the water sample from MW-9, nor has it historically been detected in any of the monitoring wells onsite Although the UST identified as be the source of contamination contained leaded gasoline, lead has not been detected in the groundwater onsite The California and Federal Water Quality Goals are presented on Table 4 Levels for TPH-g have not been established The concentrations of BTEX at the site far exceed both the California and Federal Maximum Contaminant Levels (MCL) ' Based on these water quality goals, the groundwater at the Stockton Service Center may require remediation 1 931122 Bast Bay Municipal Utility Distnet 40429500 asa 11 Stockton Svc Ctr Sitc Assessment/Rcmedial Options