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10969 Trade Center Drive <br /> Rancho Cordova , California 95670 <br /> CONESTOGA-ROVERS Telephone: (916) 889-8900 Fax: (916) 889-8999 <br /> & ASSOCIATES http 11www.crawarld.corn <br /> May 4, 2009 Reference No. 632277 <br /> Mr. Harlin Knoll <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, California 95202 <br /> Re: Soil Vapor Survey Work Plan <br /> Former Chevron Service Station #9-8632 <br /> 575 West Grant Line Road <br /> Tracy, California <br /> Dear Mr. Knoll: <br /> Conestoga-Rovers & Associates (CRA) is submitting this Soil Vapor Survey Work Plan on behalf of <br /> Chevron Environmental Management Company (Chevron) for the site referenced above. The work plan <br /> was prepared in response to the San Joaquin County Environmental Health Department (SJCEEID) letter <br /> dated March 26, 2009 (Attachment A), requesting a soil gas survey be conducted to evaluate soil vapor to <br /> determine if vapor intrusion risks exist at the site. <br /> To complete the requested assessment, CRA proposes to advance a total of four hand-augered soil <br /> borings at the south side and central portion of the site, and adjacent to the sales building. The soil <br /> borings will be completed as soil vapor wells and will be used to evaluate the vapor intrusion to indoor <br /> air pathway. The site background and CRA's proposed scope of work are described below. <br /> SITE BACKGROUND <br /> Site Description: The site is a former Chevron service station located on the northeast corner of Tracy <br /> Boulevard and Grant Line Road in a mixed commercial and residential area of Tracy, California <br /> (Figure 1). Former station facilities included a station building and service bay, three 10,000-gallon, <br /> single-walled fiberglass underground storage tanks (USTs) containing unleaded gasoline, one <br /> 1;000-gallon UST containing used-oil, one oil/water separator (sump), and two semi-hydraulic hoists <br /> (Figure 2). The fiberglass USTs were installed in 1984 when an unknown number of steel USTs and <br /> associated product lines installed in 1964, were replaced. The station was demolished in 1994, and the <br /> site is currently a used car lot. The nearest surface water bodies to the site are industrial waste ponds <br /> located approximately 1 .3 miles to the northeast (crossgradient) . <br /> Site Geology and Hydrogeology: Soil encountered beneath the site consists primarily of silty clay and <br /> discontinuous lenses of silt or clayey silt containing occasional, varying amounts of fine-grained sand. In <br /> general, soil encountered below approximately 6 to 10 feet below grade (fbg) are much stiffer than <br /> shallower soils. Soil borings advanced on the eastern boundary of the site exhibited greater amounts of <br /> silt, while borings on the western boundary contained mostly clay. <br /> Equal <br /> Employment Opportunity <br /> Employer <br /> Worldwide Engineering, Environmental, Construction, and IT Services <br />