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Y "• •---------- r it r n r i—cJVr� 1"F147t bL <br /> * I V 11vim r <br /> - 3"INVORNMRMFI <br /> AEON Ad <br /> AWWOM VA*WW 60Atrf <br /> 3 <br /> '"COR. <br /> ,w <br /> s <br /> . I <br /> rr� t <br /> «err 1 1� <br /> err"01'sY'�L `lt.ni III <br /> Internatfona!InwrPorated <br /> July 16,20M 2,1;;! 3? AM S 53 <br /> ! Project 77TO 43870 00 0105 <br /> Mr Nfichael Infuma <br /> San Joagum County Public Health Services <br /> Environmental health Division <br /> t = .304 East Webber Avenue,Third Floor <br /> Stockton,CA 95202 <br /> Re: Addendum to Work Plan for Additional Off-Site Assessment <br /> { Circle K Store#1205 <br /> -- 16470 Cambridge Street <br /> Lathrop,California <br /> Dear Mr Infuma <br /> f <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 /> 1 addendum to the work plan for off-site groundwater investigation in the vrcrruty of the <br /> subject site(Tigures 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 Worm Plan fvrAd& onal Off Site Assessment,installing <br /> > six groundwater monitoring wells to locations determined by the Gooprobe assessment <br /> This work plan includes a brief discussion of site background,scope of work,and <br /> schedule <br /> SITE DESCRIPTION AND BACKGROUND <br /> r <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 /> - Ia November 1997,Pacific Environmental Group(PW)performed oversight and <br /> -sampling during the removal of one 4,000-gallon and two 10,000-gallon underground <br /> storage caulks(UST's),product dispensers;amd associated product piping from the site <br /> during facility upgrade activities Approximately 1,241 tons of hydrocarbon impacted <br /> sod 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(TPIW at <br /> i 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(PBG,1998) <br /> In July 1998,one Geoprobe*boring was advanced to a depth of 40 feet below ground <br /> surface(bog)downgradrent(north)of the former UST excavation Laboratory analysis <br />