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{ S E C 0 R G 4 QUARTERLY SUMMARY REPORT FOURTH QUARTER 2004 76 (Former BP) Service Station #11192 1403 West Country Club Boulevard, Stockton, California City/County ID # Stockton County San Joaquin r PREVIOUS ASSESSMENT The site is located at 1403 West Country Club Boulevard in Stockton, California and is an operating 76 service station The operating facility consists of two gasoline underground storage tanks (USTs), one waste oil UST (operated by others), associated product lines, and four dispenser islands Based on Information supplied by BP and Tosco, the previous USTs (three 10,000- gallon and four 2,000-gallon USTs) were installed in 1976, and were removed in 1991 During tank removal activities, well MW-2 was destroyed Also in 1991, the three 10,000-gallon gasoline USTs were installed, which are currently in use at the site A soil gas survey was performed in 1989 A well survey was performed in 1989 that indicated the presence of a water supply well located 1,100 feet northwest from the site, and a • private well located 900 feet from the site Seven groundwater monitoring wells and two vapor extraction wells were installed at the site between 1990 and 1991 A hydropunch study and a soil vapor extraction test was conducted in 1992 Four soil borings were advanced in 1994 Eight weekly groundwater extraction events occurred between November 16, 2000 and January 2, 2001 During these events, approximately 2,400 to 3,800 gallons of groundwater were removed during each event from well MW-3 by Onyx Industrial Services (Onyx) of Benicia, California In addition, approximately 600 gallons of groundwater were removed from well MW-7 on November 16, 2000 The groundwater was extracted directly from the wells into a vacuum truck and transported to the Tosco Refinery in Rodeo, California, for disposal Approximately 27,200 gallons of groundwater were removed from the site during the eight weekly extraction events Groundwater samples were collected from well MW-3 prior to and following each of the eight extraction events A water sample was also collected from the purged groundwater during each of the eight events, prior to removal of the water from the site The estimated mass of methyl tertiary butyl ether (MtBE) removed with the extracted groundwater was calculated using the average MtBE concentration from the pre-purging and post-purging grab groundwater samples for each purging event Based on these average concentrations, an estimated total of 26 63 pounds of MtBE were removed from the site during the eight purging events between November 16, 2000 and January 2, 2001 The weekly purging was discontinued after the eight week period approved by the San Joaquin County Environmental Health Division (SJCEHD) I IConocoPhilhps\Retail Sites1111921QSSR120041402004 QSSR doc 4