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i3rovin anu Caldwi li September 23. 1991 Mr. Chuck Carmel Post Off-ice Box 5811 017-4986-2111 San Mateo, California 94402 Sub_gect: July 1991 (quarterly Report for ARCO Stall 2093. 3125 Tracy [3aulevard. Tracy, California: Pilot Program Site 1416 Dear Mr. Carmel: This report presents quarterly water levels and anal-vdcal results of groundwater sampling per-formed at ARCO Products Company (ARCO) Station 2093, located at 3425 Tracy Boulevard in Tracy, California on July 10. 1991. There are seven an-site webs (ATR-1 through ATR-7) and three off-site wells (AT:Z-9.ATR-10,and ATR-12) (Figure 1). All on-site and off-site wells were measured and sampled except ATR-7 which was inaccessible. The lid on ATR-7 is rusted shut and is being replaced. Wells ATR-10 and ATR-12 were sampled July 12, 1991. There are no monitoring wells corresponding to the identifiers ATR-8 or ATR-11. Field and Analytical Methods Brown and Caldwell personnel measured depth-to-water levels, supervised purging of each well, and collected groundwater samples at the site. Refer to Exhibit A for detailed field methods description. A summary of the groundwater measurements is presented in Table 1. All groundwater samples were analyzed for benzene,ethylbenzene,toluene,and xylenes(BETX) by U.S. Environmental Protection Agency (EPA) Method 602 and for total petroleum ltvdrocarbons as gasoline 1TPH-G) by U,S. EPA Method GC F1D/5030. Results ['Ile general groundwater flow direction beneath the station is to the northeast under a hydraulic *radient of approximately 0.002 (Figure 1). Table 2 presents the hydraulic -,radient data from previous monitoring periods. Analytical results of grountiwaler samples are summarized in Table 3, along with previGUS results. -file complete laboratory report for the July 10, 1991 sampling is presented in Exhibit B. Figure 2 presents the TPH and BETX concentrations for the July 1991 sampling event. Figure 3 presents a benzene contour map.