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Closure Report <br /> Former Mobil Bulk Plant 04-343, Tracy, California <br /> Aril 14, 1997 <br /> adsorbed-phase hydrocarbons present in the saturated zone are not readily dissolving into <br /> ground water. <br /> 5.0 SENSITIVE RECEPTORS <br /> A survey of possible sensitive receptors located at or near the site was conducted. The results of <br /> the survey are as follows: <br /> • The nearest downgradient surface water body is the Sugar Cut SIough located over 3,000 <br /> feet north of the site. <br /> • A well survey was conducted at the Department of Water Resources (DWR) in Sacramento, <br /> California by Alton Geoscience on February 3, 1997. One municipal well (02S05E22D01) <br /> was identified approximately 300 feet east of the site. This well is listed as a municipal <br /> supply well for the City of Tracy, and is reported to be 920 feet deep. The well is screened <br /> from 340 to 920 feet, with a sanitary seal depth of 200 feet. This well is not subject to <br /> impaction from the former Mobil site, and is currently not used by the city as a supply well. <br /> According to Mr. Steve Baily of the Tracy Department of Public Works (TT)PW), the <br /> �► �'` city's municipal water is supplied from deep water wells in and around Tracy, and from the <br /> Delta Mendota water supply. The nearest supply well is located 5,500 feet upgradient of <br /> the site in Lincoln Park. This well is approximately 950 feet deep and screened from <br />`i approximately 350 feet (TDPW, 1997). <br /> • The nearest school is Duncan-Russell Continuation High School, located approximately <br /> 3,000 feet east of the site. <br /> 6.0 RATIONALE FOR SITE CLOSURE <br />,. Alton Geoscience requests site closure based on the following: <br /> • The UST, ASTs, and associated piping have been removed from the site. <br /> LM <br /> • Excavation activities in 1990 were able to remove most of the hydrocarbon-impacted soil at the <br /> site. <br /> • Confirmation soil borings drilled in 1994 (SB-1 through SB-11) indicate that residual diesel- <br /> range hydrocarbons remain in soil below the site at 10.5 to 12.5 fbg (below static water level). <br /> The fine-grained, low permeability sediments that underlie the site are helping to bind any <br /> remaining soil hydrocarbons and inhibit hydrocarbon migration. The decrease in hydrocarbon <br /> 5 <br />