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SECOR www secor com <br /> INTERNATIONAL 3017 Kilgore Road,Suite 100 <br /> S E C ® R INCORPORATED Rancho Cordova CA 95670 <br /> 916 661 0400 FAx g <br /> s 916 e61 0430 Fax <br /> April 14, 2003 <br /> X14 <br /> APR 15 2403 <br /> Mr Harlan Knoll ENVIRONMENT HEALTH <br /> San Joaquin County Public Health Services PERMIT/SERVICES <br /> 304 East Weber Avenue <br /> Stockton, California <br /> RE Work Plan for Additional Assessment <br /> Tosco Station #8671 <br /> 8606 Thornton Road <br /> Stockton, California <br /> SECOR Project No 77CP 68671 00 0001 <br /> Dear Mr Knoll <br /> _This letter, prepared by SECOR International Incorporated (SECOR) on behalf of ConocoPhlllips, <br /> presents a work plan for additional site assessment at the subject site (Figures 1 and 2) The <br /> proposed assessment involves the drilling and installation of two groundwater monitoring wells, one <br /> sentry well south of the site, and one well onsite This work plan has been prepared In response to <br /> the Environmental Health Department-San Joaquin County letter dated March 13, 2003 (Attachment <br /> A) The purpose of the proposed work is to install a sentry well between the site and the San <br /> . Joaquin County Colonial Heights Municipal Well #3, which is located 260 feet south of the site and to <br /> delineate the vertical extent of MtBE in the groundwater in the source area This work plan includes <br /> a brief discussion of site background, proposed scope of work, and schedule <br /> SITE BACKGROUND <br /> The site is located at 8606 Thornton Road, Stockton, California The site is currently an operating <br /> gasoline service station that contains two gasoline LISTS, associated product lines, and dispensers <br /> In May 1998, product lines and dispensers were upgraded to meet 1998 EPA standards Analytical <br /> results from pea gravel samples collected from above the USTs and soil samples collected from the <br /> former product line and dispenser excavations indicated the presence of petroleum hydrocarbons in <br /> soil beneath the site The results of this work are documented in SECOR's report titled Removal and <br /> Replacement of Product Lines and Dispensers, dated July 22, 1998 During product line and { <br /> dispenser upgrade activities, approximately 21 tons of petroleum-Impacted soil were over-excavated <br /> from the site and disposed of at Forward Landfill <br /> On January 27 and 28, 1999, four groundwater monitoring wells (MW-1 through MW-4) were <br /> Installed onsite by SECOR The results of this work are documented in SECOR's report titled Well <br /> Installation Report, dated March 16, 1999 Since their installation, the four wells have been <br /> monitored and sampled quarterly <br /> On December 12th through 14th, 2001, one deep soil boring (SB-1) was drilled to an approximate <br /> depth of 63 feet below ground surface (bgs) and three additional groundwater monitoring wells (MW- <br /> 5, MW-6, and MW-7) were installed onsite by SECOR The results of this work are documented in <br /> SECOR's report titled Site Assessment Report, dated June 21, 2002 <br /> SECOR performed a sensitive receptor survey to identify the location of permitted water supply wells <br /> within a 2,000-foot radius of the site The sensitive receptor survey consisted of reviewing the <br /> e <br /> %ConocoPhillipsMsco Marketing186711WorkplansMPLAN sentry well install doc <br />