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r) 1 Supplemental Investigation Report BP Oil Site No 11193 C A M B R I A Stockton, California • October 13, 2000 During tank and piping replacement activities, approximately 500 cubic yards of soil were 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 Based on these concentrations and the stockpile volumes, a typical soil bulk density of 17 kilograms per liter(kg/l), and specific gravities of 0 80 for gasoline and 0 74 for MTBE, an estimated 84 pounds of TPHg and 82 pounds of MTBE were removed during tank replacement In addition, approximately 15,000 gallons of water were extracted during installation of the new underground storage tanks by TOSCO A water sample collected from the tank excavation on December 17, 1998 reported 17,000 µ.g/1 of TPHg, 1,500 ptg/l of benzene, 120,000µg/l of MTBE and 210 gg/1 of t-amyl methyl ether(TAME) No ethanol, t-butanol (TBA), dilsopropyl ether(DIPE) or ethyl t-butyl ether(ETBE) were reported 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 • In October 1999, BP collected soil and groundwater samples from six cone penetration test (CPT) borings (CB-1 through CB-6) (see Figure 2) Except for 14 mg/kg in sample CB-1-13, 27 mg/kg in sample CB-3-13 5 and 0 74 mg/kg in sample CB-4-13 5,no gasoline range organics (GRO or TPHg) were reported in the analyzed soil samples MTBE was reported at concentrations of 0 010 to 28 mg/kg in analyzed soil samples from borings CB-1, CB-2, CB-3 and CB-4 No MTBE was reported in the analyzed soil samples from borings C13-5 and CB-6 Except for 0 058 mg/kg in sample CB-3-13 5, no TAME was reported in the analyzed soil samples Grab groundwater samples from depths of 16-17 feet bgs in borings CB-1, CB-3 and CB-4 reported more than 10,000 µg/1 of GRO and MTBE and more than 25 µg/1 of benzene and TAME Where reported in grab samples from depths of 29-30 or 34-35 feet bgs in borings CB-1, CB-3 and CB-4, GRO, MTBE and TAME concentrations were at least an order of magnitude lower than in the shallower samples Grab water samples from bonngs C13-2, CB-5 and CB-6 reported less than 150µg/l of GRO and MTBE, and no benzene or TAME Currently, TOSCO is conducting interim groundwater extraction as described in their April 19, 2000 Interim Migration Control Plan Approximately 5,000 gallons of groundwater are being removed • from wells MW-1R and/or MW-2R on a weekly bans using a vacuum truck We understand that TOSCO will report findings of this interim action under separate cover 3