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. Atlantic Richfield Company Page 2 ARCO Station No 4932,Stockton Cahfonlia August 29 2002 2.0 SITE BACKGROUND 2.1 Site Setting The site is an operating AM/PM mini-mart and ARCO service station located at the intersection of Center Street and Harding Way in Stockton, California The site is located in a rmxed residential and commercial area of Stockton Facilities at the site currently include one 20,000-gallon gasoline UST, and one 22,000 gasoline UST, and associated product lines and dispensers 2.2 Summary of Previous Investigations The various environmental assessments completed at the site are summarized below A table summarizing well construction details is included as Table 1 A site plan showing well locations is included as Figure 2 Boring logs and well construction diagrams are presented as Appendix B Historical soil analytical data are presented as Appendix C Historical groundwater analytical data are presented as Appendix D Historical figures are included in Appendix E Referenced regulatory correspondence letters are included in Appendix F Between May 25 and June 9, 1999, Gettler Ryan Construction of Dublin, California removed • three 10,000-gallon double-walled fiberglass USTs and enlarged the excavation to accommodate the larger new USTs Approximately 631 tons of soil was over-excavated from the UST complex —Over-excavation of the UST complex was completed and samples _ were collected on June 9, 1999 Six samples collected from the excavation at approximately 19 feet bgs One sample contained TPHg and MtBE at concentrations of 102 mg/kg and 0 579 mg/kg, respectively No benzene or fuel oxygenates were detected in any other samples from the over-excavation During the facility upgrade, approximately 150 tons of soil was over-excavated from the product line and dispenser areas TPHg was reported in three of the six samples collected from beneath the former facilities at a maximum concentration of 5,430 mg/kg Benzene was reported in two samples at a maximum concentration of 10 6 mg/kg MtBE was reported in two samples at a maximum concentration of 55 5 mg/kg This work was summarized in SECOR's report titled Soil Sampling During USTs, Product Lane, and Dispenser Removal Activities dated December 10, 1999 In August 2000, four groundwater monitoring wells (MW-1, MW-2, MW-3, and MW-4) and one vapor extraction well (SVE-1) were installed at the site Groundwater samples collected from these wells were reported to contain TPHg, benzene, and MtBE MW-4 contained maximum concentrations of 166,000 ug/L, 10,500ug/L, and 708,000 ug/L, respectively Other detected constituents included TAME, 1,2 DCA, TBA and EtBE This work was summarized in SECOR's report titled Site Assessment Report dated November 6, 2000 1\ARCO\49321PAR\PAR doc