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Surface Water and Well Survey and CPT Investigation Report C A M B R I A BP Oil Site No 11193 Stockton, California ` December 16, 1999 Groundwater Analytical Results During the fourth quarter 1999 monitoring event, samples were collected from wells MW-3, MW-4, MW-5, MW-6, MW-7 and VW-1 (see Table 4) Well MW-2 was not sampled due to a bend in the well casing Well VW-1, which screens from 7 to 17 feet bgs, reported 340,000 µg11 of GRO, 650 µg11 of benzene and 440,000 µgn of MTBE Wells MW-3 and MW-5 reported GRO concentrations of 1,000 µg/l and 610 µg/1, respectively, and MTBE concentrations of 1,100 µg11 and 640 µg/l, respectively No BTEX constituents were reported in these wells Wells MW-4, MW-6 and MW-7 reported no GRO or BTEX constituents, a and less than 30 µg11 of MTBE CONCLUSIONS Soil beneath the site consists of shallow fill and clays underlain by silt and sand mixtures Groundwater was encountered at approximately 13 5 feet bgs during CPT sampling activities An active water-producing well, which screens from approximately 214 to 350 feet bgs, was identified approximately 315 feet west of the site MTBE concentrations of more than 30,000 ;Ag/1 were reported in groundwater samples collected from shallow groundwater near the tank vault and dispensers at the site More than 3,000 µg/l of MTBE was reported at 30-35 feet bgs near the tank vault RECOMMENDATIONS Well Replacement During tank replacement activities, well MW-1 was destroyed and well MW-2 was apparently damaged Well MW-2 will be destroyed by overdrilling with 10-inch diameter hollow-stem augers and the borehole will be converted to a 4-inch diameter well A second 4-inch diameter well will be installed adjacent to well MW-1 These wells will screen from 10 to 30 feet bgs Groundwater Monitoring Continuation of the existing groundwater monitoring program is recommended Samples will be analyzed for GRO by modified EPA Method 8015 and BTEX, MTBE and TAME by EPA Method 8260 s� 9