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l� s if I SECOR www secor com ® INTERNATIONAL 3017 Kilgore Road,Suite 100 INCORPORATED Rancho Cordova,CA 95670 i 91 -861.0400 TEL 916-861-0430 FA% January 14, 2004 JA N 16 2004 Mr Harlan Knoll kW'rr,j,VMENT San Joaquin County Environmental Health Department PE"'41T HEATH 304 East Weber Avenue, Third Floor �SERVlCjS Stockton, California 95202-2708 RE Site Assessment Report Circle K Store No 08671 8606 Thornton Road Stockton, California SECOR Project No 77CP 68671 02 0006 Site Code No 2261 Dear Mr Knoll This letter, prepared by SECOR International Incorporated (SECOR) on behalf of ConocoPhillips, presents the findings of assessment activities conducted at the site referenced above (Figure 1) The objective of this work was to investigate the lateral and vertical extent of petroleum hydrocarbons and fuel oxygenates in soil and groundwater beneath and downgradient of the site The completed scope of work consisted of the installation of three deep groundwater monitoring . wells (MW-8 through MW-10) This work was performed as described in SECOR's Work Plan for Additional Assessment dated April 14, 2003, and In accordance with the work plan approval letter from the San Joaquin County Environmental Health Department (SJCEHD) dated June 24, 2003 (Attachment 1), which requested the installation of the third deep groundwater monitoring well (MW- 9) downgradient (east) of the source area The April 14, 2003 work plan called for the Installation of an off-site deep sentry well (SW-1), which ) was to be Installed within the City of Stockton right-of-way between the site and the domestic well (DW-3) identified near Mosher Slough, approximately 260 feet south of the site However, during pre-field assessment activities, it was determined by SECOR field staff that the proposed location of the sentry well was not sufficient for monitoring groundwater quality In the vicinity of DW-3 SECOR consulted with the City of Stockton, Public Works Department (CSPWD) to determine whether a potential alternative location, a gravel road area bounding Mosher Slough to the north, was considered the City of Stockton right-of-way, and requested to install the sentry well in this area However, the CSPWD indicated that this area is considered an unfinished intersection, and therefore rejected the alternative sentry well location Another location was proposed by the CSPWD north of the gravel road area, an area that is under the jurisdiction of San Joaquin County, however, it was t determined that this area is an inadequate location for monitoring groundwater quality in between the site and well DW-3 In a site meeting between Mr Harlan Knoll and SECOR staff during the commencement of drilling activities on November 18, 2003, Mr Knoll authorized the installation of a deep well on-site near well MW-5 to monitor groundwater quality within the deeper water-bearing zone in the southern portion of the site, in place of the previously proposed off-site sentry well A description of the site background and the results of the site assessment are presented below SITE BACKGROUND The site is currently an operating gasoline service station that contains two gasoline underground storage tanks (USTs), associated product lines, and dispensers a{9 Y 11ConocoPhill ips\Tosco Marketing186711Reports\Assessment Rpt doc