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Supplemental Investigation Work Plan F BP Oil Site No. 11193 C A M B R I A Stockton, California February 25, 2000 Previous Work: During a voluntary site assessment in support of the sale of the facility in 1992,BP installed four onsite groundwater monitoring wells (MW-1 to MW-4) (see Figure 2). No total petroleum hydrocarbons as gasoline (TPHg) were reported in the analyzed soil samples from these i borings. Except for 0.087 milligrams per kilogram (mg/kg)in well MW-1 at 20 feet below ground surface (bgs), and 0.12 mg/kg in well MW-2 at 21.3 feet bgs, no benzene was reported in the , analyzed soil samples. Groundwater samples collected in December 1992 reported up to 2,200 micrograms per liter (µg/l) of TPHg and 120 µg/1 of benzene. Based on the results of this investigation, a release was reported. fn March 1994, BP installed one onsite monitoring well (MW-5) and two offsite monitoring wells (MW-6 and MW-7) (see Figure 2). No TPHg was reported in the analyzed soil samples from these borings. Except for 0.13 mg/kg in well MW-5 at 16 feet bgs, no benzene was reported in the analyzed soil samples. Ihl November 1994,,TOSCO installed one vapor extraction well (VW-1), and sampled soil and groundwater from two hydropunch borin s (THP-1 and THP-2) and soil beneath two dispensers F (TD-2 and TD-3) (see Figure 2). 2,100 mg/kg and 1,400 mg/kg of TPHg were reported in samples 1 TD-2 and TD-3, respectively. No TPHg was reported in the analyzed soil samples from the hydropunch borings. Except for 0.03 nig/kg in boring THP-2 at 15 feet bgs, no benzene was reported in the analyzed soil samples from beneath dispensers or the hydropunch borings. Grab m water saples from borings THP-1 and THP-2 reported 65 Lig/l and 6,900 µg11 of TPHg, respectively, and 7.3 µg/l and 1,900 µg/l of benzene, respectively. MTBE analysis was not requested for this investigation. 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 mg/kg of MTBE. 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 mg/kg of benzene, and less than 5.1 mg/kg of MTBE. 2