SITE INFORMATION AND CORRESPONDENCE

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ii 1, 31 feet as recorded by the PHS/EHD inspector during-the well installations. Thee screen interval in MW-7 is unknown. Groundwater was measured at 14.46 feet in MW-5 and 13.85 feet in MW-6 July 12, 1996. With the recent winter rains the groundwater elevation is expected to rise. - " Current trends in groundwater based on MTBE indicate an increasing trend in MW-1 and MW-2 nearest the tank bed and in MW-6 downgradient and oft site. s MW-5 is beginning to show the presence of MTBE. The past three analytical samples of the upgradient well MW-3 resulted in the presence of MTBE. Benzene a levels are following the same trends as MTBE rising in MW 1,2 and 5. Your request to sample MW 3,4 and 7 annually'may result in missing the migration of MTBE in an upgradient direction. W 1 The sandy soil beneath this site is amenable to remedial technologies and plume . migration. Monitoring wells 1 and 2 are 5 feet over screen and hydrocarbon levels are still rising. The plume has not shown signs of attenuating since the leak began in 1989. The increasing trends of MTBE, now at 20,000 ppb and benzene now at 990 ppb, in MW-2 indicate that new product may be reaching ' groundwater. This data does not indicate that this is a stable or a declining plume. PHSIEHD recommends that rather than reduce sampling frequency in the upgradient wells you prepare a workplan that will describe a method to investigate and evaluate remedial alternatives for active remediation. This agency also requires the boring logs for MW:5,6 and 7 and recommends sampling of the vapor well by BP Oil. E: For additional information please call Steve Sasson , senior RENS, at (209) 468 3459. Donna Heran, RENS, Director Environmental Health Division 5 S en"Se n, ni" or REHS ; Margare Lagorio, REHS Site Mitigation Unit E' . Supervisor'i cc: Elizabeth Thayer, CVRWQCB } F} i f