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F > Supplemental Investigation Work Plan C A M B R I A BP Oil Site No. 11193 Stockton, California February 25, 2000 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 ung/kg of MTBE for the tank excavation stockpile, 48 mg/kg 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 1.4 kilograms per liter (kg/1), 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(see Appendix A). In addition, approximately 15,000 gallons of water were extracted during installation of the new j underground storage tanks. A water sample collected from the tank excavation on December 17, 1998 reported 17,000 lig/l of TPHg, 1,500 µg/l of benzene, 120,000 µg/l of MTBE and 210 µg/l.of t-amyl methyl ether(TAME). No ethanol,t-butanol, di-isopropyl ether or ethyl t- I butyl ether 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 (see Appendix A). 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 sample's. 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 k reported in the analyzed soil samples from borings CB-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, C13-3 and CB-4 reported more than 10,000 µg11 of GRO and MTBE and more than 25 µg/l of benzene and TAME. In addition, the water sample from this depth in boring CB-4 also reported 8.0 µg/l toluene, 160 µg/l of ethylbenzene and 110 µg/l of xylenes. 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. No benzene,toluene, ethylbenzene or xylenes (BTEX) were reported in these samples. Grab water samples from borings CB-2 CB-5 and CB-6 reported less than 150µg/l of GRO and MTBE, and no BTEX or TAME. 3