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SECOR <br /> . International Incorporated <br /> August 16, 2000 <br /> Project 077 42070 3 10 <br /> Mr Mike Infurna <br /> San Joaquin County Environmental Health Department <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, CA 95202 + <br /> Re Work Plan for Additional Site Assessment <br /> ARCO Station #6020 <br /> 1711 E Yosemite Avenue <br /> Manteca, California <br /> Dear Mr Infurna <br /> This letter, prepared by SECOR International Incorporated (SECOR) on behalf of Atlantic <br /> Richfield Company (ARCO), presents a work plan for the installation of four groundwater <br /> monitoring wells at the subject site (Figures i and 2) The purpose of the proposed work <br /> is to define the lateral and vertical extent of petroleum hydrocarbons in soil and <br /> groundwater beneath the site This work plan has been prepared in response to San <br /> Joaquin County Environmental Health Department (SJCEHD) letter, dated April 19, 1999 <br /> (Attachment A) This work plan includes a brief discussion of site background, proposed <br /> scope of work, and schedule <br /> SITE BACKGROUND <br /> The site is an operating ARCO service station located on the north side of Yosemite <br /> Avenue east of Highway 99 in Manteca, California ARCO previously installed <br /> groundwater monitoring wells to investigate a previous release of petroleum hydrocarbons <br /> at the site Based upon four years of groundwater monitoring data indicating low to <br /> nondetectable levels of petroleum hydrocarbons in groundwater, ARCO requested site <br /> closure In 1996, ARCO was granted closure from the SJCEHD and all groundwater <br /> monitoring wells were subsequently destroyed <br /> Excalation and removal of three gasoline underground storage tanks (USTs) and <br /> associated product lines and dispensers were performed on April 21, 1999 Sampling <br /> activities associated with removal of the USTs and product lines at the site revealed the <br /> presence of petroleum hydrocarbon impacted soil and groundwater in the vicinity of the <br /> USTs TPHg and MtBE were reported at the maximum concentrations of 1,430 mg/kg <br /> and 20 8 mg/kg in soil samples collected after over-excavation was performed <br /> Additionally, three groundwater "grab" samples collected from the within the UST cavity <br /> were reported to contain MtBE at concentrations ranging from 180 micrograms per liter <br /> (µg/L) to 310 (µg/L) UST removal soil and groundwater analytical data and the sample <br /> location map is included as Attachment B <br /> 3017 Kilgore Road, Suite 100, Rarac ho Coidoua, CA 95670 916 861 o400 916 861 0430 Fcax www Secor com <br />