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4 ¢ <br /> o. <br /> k 4 yURS <br /> [RECOVED <br /> MAR 2 3 2004 <br /> March 18, 2004 <br /> ENVIRONMENT HEALTH <br /> PERMIT/SERVICES <br /> Mr. Harlin Knoll 02093 <br /> San Joaquin County Environmental Health Department 06.0 <br /> 304 E Weber Street,Third Floor <br /> Stockton, CA 95202 <br /> RE: Trend Analysis of Contaminant Concentrations Over Time <br /> ARCO Service Station No.2093 <br /> 3425 Tracy Boulevard,Tracy,California <br /> Dear Mr. Knoll: I <br /> E <br /> URS Corporation Americas (URS), on behalf of Atlantic Richfield Company (ARCO - a BP affiliated <br /> i company), has prepared this letter to document [he trend of contaminant concentrations over time at <br /> ARCO Station No. 2093 located at 3425 Tracy Boulevard, Tracy, California. The San Joaquin County <br /> Environmental Health Department (SJCEHD) requested the trend analysis of contaminant <br /> concentrations over time in an electronic mail correspondence dated February 13, 2004(Attachment A). <br /> Background Information <br /> Currently, the site is operated as an ARCO gasoline station with an AM/PM mini-mart. The site is <br /> bounded by commercial property to.the west and north, Tracy Boulevard to the east, and West Clover <br /> Road to the South. The majority of the site is paved. <br /> r Site structures include double-walled fiberglass gasoline underground storage tanks (USTs), two pump <br /> islands, and the AM/PM mini-mart. During previous site work, 12 groundwater monitoring wells <br /> (ATR-1 through ATR-12), 7 soil vapor extraction wells (VES-1 through VES-7), 3 air sparging (AS) <br /> i wells (S-1 through S-3), 1 groundwater monitoring/AS well (SMWA), and one groundwater extraction <br /> well (TEX-1) have been installed at the site. TEX-1 was properly destroyed by URS on January 26, <br /> 2004. Currently, the site is on a quarterly groundwater monitoring schedule. Air sparging is ongoing at <br /> the site. Well locations are shown on Figure 1. <br /> Well Contaminant Trends <br /> Based on discussions with SJCEHD, graphs showing the contaminant trends were generated for all <br /> wells that historically contained contamination. The wells included in the trend analysis are ATR-I <br /> through ATR-8. Wells ATR-9 through ATR-12 and TEX-1 never identified detectable concentrations <br /> of contaminants and were therefore not evaluated. In addition, well SMW-1 is an'air sparging well that <br /> has not been sampled since September 1998; therefore, SMW-1 is also not included in the trend <br /> analyses. The trend analysis of wells ATR-1 through ATR-8 is discussed below. <br /> URS Corporation <br /> Crown Corporate Center <br /> 2870 Gateway Oaks Drive, Suite 300 <br /> Sacramento,CA 95833 <br /> Tel: 916.679.2000 <br /> i Fax:916.679.2900 <br />