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T Site Investigation Report BP Oil Site No 11191 Stockton, California . C A M B R I A March 29, 2002 Surface Water Bodies and Water Supply Wells Mosher Creek is located approximately '/2-mile north of the site A June 18, 2001 SJCPHS letter indicated that a recently installed City of Stockton water supply well (well 3-2) is located approximately 2,000 feet to the south of the site at 7400 West Lane Frontage Based on an August 21, 2001 telephone conversation with Mark Madison of the City of Stockton Department of Municipal Utilities (CSDMU), well 3-2 was drilled to a total depth of approximately 625 feet and is scheduled to begin water production in the spring or summer of 2002 Well 3-2 is sealed with cement grout from the surface to 144 feet bgs and with bentonite from 376 to 386 feet bgs In addition, information obtained from the CSDMU indicates that two water supply wells (Nos 20 and 21) and one test boring (No 13) were drilled to approximately 600 feet at locations approximately i/2-mile from the site Wells 20 and 21 are sealed with cement mortar from the surface to 70 and 60 feet bgs, respectively Previous Activities Eleven soil borings were advanced to depths of up to 80 feet below ground surface (bgs) during site investigations conducted at the site between 1992 and 1995 (see . Appendix B) In 1998, TOSCO replaced the underground storage tanks, dispensers, and associated piping Site Hydrogeology The site is underlain primarily by silt and sand to the total depth explored of 80 feet bgs Groundwater was not reported during the previous site investigations Hydrocarbon Distribution Soil analytical results for samples collected from the eleven soil borings indicated up to 0 15 milligrams per kilogram (mg/kg) of benzene and 0 37 mg/kg of (suspected) methyl tert butyl ether (MTBE) (see Appendix A) No hydrocarbons were reported in the deepest analyzed samples or at depth in adjacent borings(e g , borings B-4 and B-5) Based on these results, the extent of hydrocarbons in soil was considered defined Soil analytical results for samples collected beneath the underground storage tanks during 1998 replacement activities reported up to 0 0083 mg/kg benzene, 24 mg/kg MTBE, and 120 mg/kg tert-butyl alcohol (TBA) Analyzed soil samples collected beneath the dispensers and piping reported no benzene or TBA, and up to 0 52 mg/kg MTBE Additional oxygenates (i e , ethanol, di-isopropyl ether, ethyl tert-butyl ether and tert-amyl methyl ether) were not reported in the analyzed soil samples 2