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SAN dOAGM OOUNIr <br /> atnnRONtrt;�rKNw.tM <br /> �OtE��RM11� _ <br /> ❑ AWO d <br /> 0 AW0V"VM*M1M`ft1Ift <br /> R r. a�NMtN <br /> Dees <br /> Avvrovai.taMnds onyx•M.c Nlllilt <br /> twoon and does not nNr 1 or M/AM • <br /> deviation from requirements of--M.,.. <br /> International Incorporated <br /> July 16,2002 �' J',1:. '..`, `- 53 <br /> Project 77TO.43870.00.0106 <br /> Mr.Michael Infuma <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> -304 East Webber Avenue,Third Floor <br /> Stockton,CA 95202 <br /> Re: Addendum to Work Plan for Additional Offsite Assessment <br /> Circle K Store#1205 <br /> 16470 Cambridge Street <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 comer of Cambridge Street and Louise Avenue in <br /> -:- - - Lathrop,California,and is an operating Circle K Mini Mart and TOSCO service station..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®boring was advanced to a depth of 40 feet below ground <br /> surface(bgs)downgradient(north)of the former UST excavation. Laboratory analysis <br />