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Surface Water and Well Survey and CPT Investigation Report CAM B R I A BP Oil Site No 11193 Stockton, California December 16, 1999 In December 1998, TOSCO replaced the underground storage tanks and associated piping at the site The tank vault was overexcavated to 16 feet bgs and areas adjacent to several dispensers were excavated to depths of up to 10 feet bgs (see Figure 2) Soil samples collected from the bottom of the tank excavation reported less than 31 mg/kg of TPHg, less than 0 3 mg/kg of benzene, and 11 to 80 mglkg of MTBE (see Appendix A) Following overexcavation of the southeastern dispenser area, soil sample D3-2-10 5 reported 29,600 mg/kg of TPHg, 227 mg/kg of benzene, and less than 125 mg/kg of MTBE (see Figure 2) Soil samples collected from beneath the remaining piping and dispenser areas reported less than 20 mg/kg of TPHg, less than 0 12 of benzene, and less than 5 1 mg/kg of MTBE During tank and piping replacement activities, approximately 500 cubic yards of soil was removed from the tank vault, 100 cubic yards were initially removed from the piping trench, and 90 cubic yards were overexcavated from the piping trench Composite samples reported no TPHg and an average of 58 mg/kg of MTBE for the tank excavation stockpile, 48 mglkg of TPHg and no MTBE for the piping stockpile, and 279 mg/kg of TPHg and no MTBE for the piping • overexcavation stockpile (see Appendix A) Based on these concentrations and the stockpile volumes, a typical soil bulk density of 14 kg/l, and specific gravities of 0 80 for gasoline and 0 74 for MTBE, an estimated 69 pounds of TPHg and 67 pounds of MTBE were removed during tank removal replacement In addition, approximately 15,000 gallons of water were extracted during installation of the new underground storage tanks A water sample collected from the tank excavation on December 17, 1998 reported 17,000 µg/1 of TPHg, 1,500 µg/1 of benzene, 120,000 µg/l of MTBE and 210 µg11 of t-amyl methyl ether (TAME) No ethanol, t-butanol (TBA), di-isopropyl ether (DIPE) or ethyl t-butyl ether (ETBE) were detected in the analyzed samples Based on these concentrations and the extraction volumes, and the specific gravities described above, an estimated 2 1 pounds of TPHg and 15 pounds of MTBE were removed during dewatering activities (see Appendix A) 3