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t <br /> International incorporated <br /> October 29, 2001 OCT 3 0 2001 <br /> Project 077.43808.416 ENVIRON �l 6tpQI 4 <br /> Ms. Carole Oz pERMITISERVICES <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> P.O. Box 2009 <br /> Stockton, CA 95201 <br /> Re: Work Plan for 5-Day Dual Phase Extraction Event <br /> Tosco (former BP) Service Station#11193 <br /> 3202 West Hammer Lane <br /> Stockton, California <br /> Dear Ms. Oz: <br /> This letter, prepared by SECOR International Incorporated (SECOR) on behalf of Tosco <br /> Corporation (Tosco), a subsidiary of Phillips Petroleum Company,presents a work plan <br /> for performing a 5-day dual phase extraction (DPE)remediation event at the subject site <br /> (Figure 1 —Cambria). Tosco is proposing to initiate short-term DPE at the site using a <br /> mobile extraction and treatment system supplied by SECOR. The SECOR DPE system <br /> is designed to extract soil vapor and groundwater simultaneously from the subsurface. <br /> The purpose of this event is to reduce the concentrations of hydrocarbons in groundwater <br /> beneath the site. <br /> This work plan includes a brief discussion of site background and previous <br /> investigations, proposed scope of work, and schedule. <br /> SITE BACKGROUND AND PREVIOUS INVESTIGATIONS <br /> The site is located at 3202 West Hammer Lane in Stockton, California, and is an <br /> operating 76 service station. The site currently contains three gasoline USTs, associated <br /> product lines, and dispenser. <br /> In April 1987,KEI observed the removal of one 1,000-gallon waste oil tank on the <br /> southwestern portion of the site. One soil sample was collected from the base of the <br /> excavation at approximately 10 feet below ground surface (bgs). Laboratory analytical <br /> results detected gravimetric waste oil as petroleum oil at 55 parts per million (ppm) <br /> (EMCON, 1994). <br /> Between December 3,4 and 10, 1992, RESNA performed a preliminary site assessment <br /> for British Petroleum (BP) by drilling four exploratory soil borings (B-1 through B-4) to <br /> total depths of 31.5 to 36.5 feet bgs and converting them to Groundwater Monitoring <br /> Wells MW-1 through MW-4. Wells MW-1 and MW-2 were installed on the southeast <br /> and northwest corners, respectively, of the underground storage tanks (USTs), Well <br /> MW-3 was installed on the west end of the northern dispenser island and Well MW-4 <br /> was installed between the former waste oil tank and the new waste oil tank. Laboratory <br /> analytical results for soil detected maximum concentrations of benzene at 0.1200 ppm <br /> 3017 Kilgore Road,.Suite 100,Rancho Cordova, CA 95670 916.861.0400 916.861.0430 Fax www.secor.com <br />