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r <br /> �-_•' SECOR —1W.secorcom <br /> INTERNATIONAL 3017 Kilgore Road, <br /> Suite 100 <br /> S E C O .R INCORPORATED Rancho Cordova,CA 95670 <br /> 916-861-0400 TEL <br /> 916-861-0430 FAX <br /> July 27, 2004 <br /> Mr. Michael Infurna hi <br /> San Joaquin County Environmental Health Department ZM <br /> Unit IV— Site Mitigation ✓ ��� <br /> 304 East Weber Avenue U4 2 O <br /> Stockton, CA 95202 EPIR� O, 9 '?004 <br /> RE: Work Plan for Additional Site Assessment FRMIr�S q��FAcry <br /> 7-Eleven Store #14117 FS <br /> 2725 Country Club Boulevard <br /> Stockton, California 95204-3937 <br /> SECOR Project No.: 77EL.14117.04.0104 <br /> Dear Mr. Infurna: <br /> This work plan, prepared by SECOR International Incorporated (SECOR) on behalf of 7- <br /> Eleven Inc., proposes installing offsite monitoring wells and soil borings to delineate the <br /> vertical and lateral extent of methyl-tert-butyl ether (MtBE) and tert-butyl alcohol (TBA) in <br /> soil and groundwater offsite from 7-Eleven Store #14117. SECOR proposes installing two <br /> offsite groundwater monitor wells, advancing three offsite soil borings, and advancing three <br /> cone penetrometer (CPT) borings at the subject site (Figures 1 and 2). Due to the <br /> increasing concentrations of TBA in groundwater adjacent to the site, the San Joaquin <br /> County Environmental Health Department (SJCEHD) has requested SECOR submit a <br /> workplan for additional assessment of hydrocarbon contamination. <br /> In particular, this work plan will (1) evaluate the limits of hydrocarbon contamination in deep <br /> portions of soil and groundwater onsite and the hydrocarbons dissolved in groundwater <br /> downgradient of the site, and (2) delineate the lateral extent of shallow contamination in soil <br /> and groundwater north and southeast of the site. Data derived from the proposed borings <br /> and monitor wells will be used to define the boundaries of the hydrocarbon plume and <br /> direction of migration. The proposed monitor wells will also be incorporated into the <br /> regularly scheduled quarterly monitoring and sampling program. <br /> The site is an active 7-Eleven convenience store and gasoline station. The retail gasoline <br /> station consists of one dispenser island and two 10,000-gallon underground storage tanks <br /> (USTs) (Figure 2). <br /> �I <br /> BACKGROUND <br /> On July 17, 1998, three 10,000-gallon single-walled USTs were removed from the site. The <br /> UST excavation was extended to the east, and two new 10,000-gallon double-walled steel <br /> USTs were installed (Figure 2). The new tanks were installed in a tank pit located east of <br /> the original UST locations. One ten-inch diameter Schedule 40 PVC conductor casing was <br /> installed in the new UST pit between the new tanks for future installation of well MW-2. <br /> File:7-11/14117 WP for additional assessment(July 04).doc <br />