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> SC�COR www.secor.com <br /> INTERNATIONAL 3017 Kilgore Road,Suite 100 <br /> S E C O R INCORPORATED Rancho Cordova,CA 95670 <br /> 916-861-0400 TEL <br /> 916-861-0430 FAX <br /> RECCMWED <br /> S E P 16 2003 <br /> September 15, 2003 ENVIRONMENT HEALTH <br /> PEI;iUIiT/SERVICES <br /> Ms. Vicky McCartney <br /> San Joaquin County Environmental Health Division <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, California 95202-2078 <br /> Re: Revised Interim Remedial Action Plan and Work Plan for <br /> Ozone Sparge Well Installation and Additional Off-Site Assessment <br /> Tosco (Former BP) Service Station No. 11193 <br /> 3202 West Hammer Lane <br /> Stockton, California <br /> SECOR Project Nos.: 77CP.60193.00.00031 <br /> 77BP.50193.00.0447 <br /> Dear Ms. McCartney: <br /> This letter, prepared by SECOR International Incorporated (SECOR) on behalf of ConocoPhillips and <br /> BP, presents a summary of current interim remediation activities via groundwater batch extraction at <br /> the site, a proposal to replace the interim migration control program with the installation of an ozone <br /> sparging (OS) system, and a work plan for OS well installation and further off-site delineation of <br /> dissolved petroleum hydrocarbons and methyl tertiary butyl ether (MtBE) in the vicinity of <br /> downgradient well MW-6. The installation of a permanent OS system will facilitate the removal of <br /> petroleum hydrocarbons and MtBE and inhibit further migration of the dissolved plume beneath the <br /> site. A summary of the site background and previous investigations and remedial action, a synopsis <br /> of the current interim migration control program, the proposed revised interim remedial action plan <br /> (IRAP), proposed work plan for OS well installation and additional off-site assessment, and a <br /> schedule of implementing the aforementioned work activities is presented below. <br /> SITE BACKGROUND <br /> The site is situated in a mixed commercial/residential area on the southwest corner of West Hammer <br /> Lame and I4Iley Drive in Stockton, California (Figure 1).`The current station configuration consists of <br /> two 12,000-gallon double-walled gasoline underground storage tanks (USTs), two dispenser islands, <br /> associated product lines, and a station building (Figure 2). <br /> Historical files indicate that British Petroleum (BPKacquired the site from Mobil in May 1989. The <br /> gasoline service station operated under BP ownership until Tosco purchased the property in August <br /> 1994. Historical UST permit application information suggests that the site historically operated as a <br /> gasoline service station since at least 1978 (EMCON, 1994). <br /> PREVIOUS INVESTIGATIONS AND REMEDIAL ACTION <br /> In April 1987, KEI observed the removal of one 1,000-gallon waste oil UST on the southwestern <br /> portion of the site. One soil sample was collected from the base of the excavation at approximately <br /> 10 feet below ground surface (bgs). Laboratory analytical results reported gravimetric waste oil as <br /> petroleum oil at 55 parts per million (ppm, EMCON, 1994). <br /> l:1ConocoPhillips\Tosco Marketing1111931Reports\Revised IRAP&WP.doc <br />