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SECOR www secor com <br /> Q� <br /> INTERNATIONAL 3017 Kilgore Road Suite 100 a <br /> S E C ® R INCORPORATED Rancho Cordova CA 95670 4' <br /> 916-861-0400 TEL <br /> 916-861-0430 FAX <br /> �DL--n WDD <br /> S F P 0 9 2004 <br /> September 7, 2004 ENVIRWVIVIENT HEALTH <br /> Mr Michael Infurna PERMIT/SERVICES <br /> San Joaquin County Environmental Health Department <br /> 304 East Webber Avenue, Third Floor <br /> Stockton, CA 95202 k <br /> Re Results of Geoprobe Assessment <br /> Circle K Store No 01205 <br /> 16470 Cambridge Street, Lathrop, California <br /> Dear Mr Infurna <br /> This letter, prepared by SECOR International Incorporated (SECOR) on behalf of ConocoPhillips, <br /> presents the findings of assessment activities at the site referenced above (Figure 1) The objective <br /> of this work was to delineate the lateral extent of petroleum hydrocarbons in groundwater <br /> downgradient of the site and to determine proper locations of monitoring wells The scope of work <br /> consisted of the advancement of five geoprobe borings (GP-10 through GP-14) This work was = <br /> performed as described in SECOR's Addendum to Work Plan For Additional Off-Site Assessment, <br /> dated October 13, 2003, and was approved by San Joaquin County Environmental Health <br /> . Department (SJCEHD) in their letter dated January 6, 2004 (Attachment A) <br /> SITE DESCRIPTION AND BACKGROUND <br /> The site is located on northeast corner of Cambridge Street and Louise Avenue in Lathrop, California, <br /> and is an operating Circle K Mini Mart and 76 service station <br /> In November 1997, Pacific Environmental Group (PEG) performed oversight and sampling during the <br /> removal of one 4,000-gallon and two 10,000-gallon underground storage tanks (UST's), product <br /> dispensers, and associated product piping from the site during facility upgrade activities <br /> Approximately 1,241 tons of hydrocarbon-impacted soil was excavated from beneath the UST's and <br /> from the new tank pit excavation Additionally, approximately 17,000 gallons of hydrocarbon- <br /> impacted groundwater was pumped from the new tank pit excavation Soil samples collected from <br /> the excavated 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) was reported in <br /> the excavation soil samples at concentrations ranging from 0 19 ppm to 3 6 ppm (PEG, 1998) <br /> In July 1998, one Geoprobe ®boring was advanced to a depth of 40 feet below ground surface (bgs) <br /> downgradient (north) of the former UST excavation Laboratory analysis of soil samples collected k <br /> from GP-1 at 10 feet bgs reported maximum concentrations of TPHg and MtBE at 1,900 ppm and <br /> 0 31 ppm, respectively Laboratory analysis of grab groundwater samples collected from GP-1 <br /> contained concentrations of TPHg and MtBE of 52,000 ppb and 61 ppb, respectively (PEG, 1999) <br /> From August through September 1998, IT Corporation (IT) drilled and installed four groundwater <br /> monitoring wells (MW-1 through MW-4) to approximate depths of 26 to 28 feet bgs During the <br /> installation of well MW-4, the drill auger broke through a City of Lathrop water main releasing <br /> approximately 600,000 to 1,000,000 gallons of water Laboratory analysis of soil boring samples <br /> reported maximum concentrations of 6,800 ppm TPHG in MW-3-16' and 7 2 ppm MtBE in MW-2-11' <br />