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Emcon <br /> 1433 North Market Boulevard • Sacramento,California 95834-1943• (916)928-3300 • Fax(916)928-3341 <br /> June 14, 1995 <br /> Project 0805-152.03 <br /> Mr.Kyle Christie <br /> ARCO Products Company <br /> 2155 South Bascom, Suite 202 <br /> Campbell,California 95008 <br /> Re: Workplan to Conduct an Additional Subsurface Investigation for ARCO Service <br /> Station No. 6100 at 25775 South Patterson Pass Road, Tracy, California <br /> Dear Mr. Christie: <br /> At the request of ARCO Products Company (ARCO), EMCON has prepared this <br /> workplan to conduct an additional subsurface investigation at the subject site (see <br /> Figure 1). The purpose of this investigation is to delineate the lateral extent of residual <br /> hydrocarbons previously detected in soil beneath the subject site. During previous <br /> investigations, the lateral extent of gasoline hydrocarbons in soil was delineated except for <br /> an area southeast of the site (see Figure 2). The proposed investigation will include drilling <br /> four soil borings south of Patterson Pass Road and installing vapor extraction wells, if <br /> needed, to be used for future soil remediation. <br /> PREVIOUS WORK <br /> In June 1990, at the request of ARCO, RESNA Industries (RESNA [formerly Applied <br /> GeoSystems]) observed drilling of five soil borings (B-1 through B-5) at the site (Applied <br /> GeoSystems, July 16, 1990, Report No. 30041-1). Gasoline hydrocarbons were detected <br /> in soil samples collected from the borings. <br /> Roux Associates (Roux) conducted an investigation from November 1990 to February <br /> 1991 in conjunction with the removal of five underground storage tanks and associated <br /> product delivery lines (Roux, May 29, 1991, Report No. AR06776W). The presence of <br /> hydrocarbons in soil within the tank cavity necessitated the excavation of the cavity to <br /> depths ranging from 15 to 25 feet below ground surface (bgs). Soil samples collected from <br /> the limits of the overexcavated tank cavity contained concentrations of total petroleum <br /> hydrocarbons as gasoline (TPHG) up to 7,400 parts per million. Four new tanks were <br /> installed in the new tank cavity. <br /> In October and November 1991 and June 1992, RESNA observed drilling of 20 soil <br /> borings (B-6 through B-25) and construction of 15 vapor extraction wells. Residual <br /> gasoline hydrocarbons were detected in soil beneath the dispenser islands, between the <br /> underground gasoline storage tanks and the dispenser islands, along the north and west <br /> SAC1N:\P10\0805\08051520.3AL-94\dm:1 <br />