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r <br /> SECOR <br /> r ' International Incorporated <br /> July 16, 2002 S3 <br /> Project 77TO 43870 00 0106 <br /> Mr Michael Infurna <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 East Webber Avenue, Third Floor Dv <br /> Stockton, CA 95202 <br /> Re: Addendum to Work Plan for Additional Off-Site Assessment <br /> Circle K Store#1205 <br /> 16470 Cambridge Street 7 <br /> Lathrop, California <br /> Dear Mr Infuma <br /> This letter, prepared by SECOR International Incorporated (SECOR) on behalf of Tosco <br /> Corporation (Tosco), a subsidiary of Phillips Petroleum Company, provides an <br /> addendum to the work plan for off-site groundwater investigation in the vicinity of the <br /> subject site (Figures 1 and 2) The purpose of the above work is to delineate the <br /> hydrocarbon impact of groundwater off-site This addendum to the workplan deals with <br /> phase three mentioned in the Work Plan for Additional Off-Site Assessment, installing <br /> six groundwater monitoring wells in locations determined by the Geoprobe assessment <br /> This work plan includes a brief discussion of site background, scope of work, and <br /> schedule <br /> SITE DESCRIPTION AND BACKGROUND <br /> The site is located on northeast corner of Cambridge Street and Louise Avenue in <br /> Lathrop, California, and is an operating Circle K Mini Mart and TOSCO service station <br /> In November 1997, Pacific Environmental Group (PEG) performed oversight and <br /> sampling during the removal of one 4,000-gallon and two 10,000-gallon underground <br /> storage tanks (UST's), product dispensers, and associated product piping from the site <br /> during facility upgrade activities Approximately 1,241 tons of hydrocarbon impacted <br /> soil was excavated from beneath the UST's and from the new tank pit excavation <br /> Additionally, approximately 17,000 gallons of hydrocarbon impacted groundwater was <br /> pumped from the new tank pit excavation Soil samples collected from the excavated <br /> former tank pit contained total petroleum hydrocarbons as gasoline (TPHg) at <br /> concentrations ranging from 130 ppm to 5,800 ppm Methyl tert-butyl ether (MtBE) <br /> was reported in the excavation soil samples at concentrations ranging from 0 19 ppm to <br /> 3 6 ppm (PEG, 1998) <br /> In July 1998, one Geoprobe e boring was advanced to a depth of 40 feet below ground <br /> surface (bgs) downgradient (north) of the former UST excavation Laboratory analysis <br /> 3017 Kilgore Road, Suite 100, Rancho Cordova, CA 95670 916 861 0400 916 861 0430 Fax www secor com <br />