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Phase I Update and Pre-Gas Station Phase 11 Report Proposed Safeway Store#1769 Gas Station Stockton, Califomia December 12, 2000 200 feet east of the 7-11 station. Based on file information reviewed by ATC at the SJCEMD, groundwater has been impacted by petroleum hydrocarbons at both sites. According to a second quarter June 1999 groundwater monitoring report prepared for the Exxon site and reviewed by ATC, several gasoline USTs were removed from the site in 1991. Both soil and groundwater contamination was discovered during the UST removals. Groundwater monitoring wells were subsequently installed and sampled and groundwater was found to contain gasoline, benzene, toluene, ethyl benzene, xylenes (BTEX) and MTBE. As of the 1999 quarterly report, gasoline and BTEX compounds had not been recently detected in groundwater; however, MTBE was detected at a concentration of 60 parts per billion (ppb). The groundwater flow direction at this site was reported to be consistently east-northeast. According to Mr. Mike Infurna of the SJCEMD, groundwater remediation is on going at this site. According to a November 1998 site assessment report prepared for the 7-11 site and reviewed by ATC, gasoline USTs were removed from the site in July 1998 and replaced with double-walled USTs. According to Mr. Infurna of the SJCEMD, it was evident that a catastrophic gasoline release had occurred at this site, as a substantial amount of free product was present in the UST pit after removal. Soil and groundwater confirmation sampling conducted during the UST removals detected benzene at concentrations of 7,200 ppb in soil and 9,740 ppb in groundwater. Gasoline was also detected in groundwater at a concentration of 1,930,000 ppb (free product). ATC's file review did not indicate whether the samples were analyzed for MTBE. According to Mr. Infurna, four monitoring wells have since been installed at the 7-11 site. MTBE was detected at concentrations up to 2,000 pg/L in groundwater during third quarter 2000 well sampling at the 7-11, according to Mr. Infurna. MTBE was detected at a concentration of 200 pg/L in well MW-3 at the 7-11 site, which is located closest to the Safeway proposed gas station pad. The site investigation is on going as the extent of contamination has yet to be defined, according to Mr. Infurna. The groundwater flow direction at the 7-11 site was east-northeast, according to information reviewed by ATC. However, Mr. Infurna indicated that third quarter 2000 water level data from the 7-11 monitoring wells show that groundwater is flowing due west, which consistent with the west-southwest regional gradient expected in this area. As the groundwater table is expected to be relatively flat, this variability in groundwater flow direction may be due in part to pumping influences from several known nearby domestic wells and tidal influences from the nearby Sacramento River located south and west of the site. PAPROJECr&,We"y%L284M)ddo 103\1789_EA_Update.doc 5 e