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Closure Report <br /> Former Mobil Bulk Plant 04-343, Tracy, California <br /> April 14, 1997 <br /> 1.0 INTRODUCTION <br /> This report presents a formal, site closure request for former Mobil Bulk Plant 04-343, located at 500 <br /> East Grantline Road in Tracy, California(Figure 1). The objectives of this report are to: <br /> �.- • Formally present the groundwater monitoring and sampling results from the first quarter of <br /> 1997; <br /> ''" • Summarize the findings and conclusions of previous source removal, site assessment, and <br /> remedial activities conducted at the site; and, <br /> `' • Provide sufficient risk management information to support site closure with no further action. <br /> Ir <br /> 2.0 STTE DESCRIPTION <br /> L. Site Status: The site is currently a fenced vacant lot (Figure 2). The site was formerly a <br /> bulk fuel distribution facility operated by Mobil Oil Corporation. Plant <br /> operations were discontinued in 1988. All structures were removed from the <br /> ,. property in 1988, including one 1,000-gallon underground gasoline storage <br /> tank (UST), four 10,000-gallon aboveground diesel fuel storage tanks (ASTs), <br /> and the associated piping. The site is bound by vacant lots to the east and <br /> �. south. Doane Products Company is located to the west, across the Southern <br /> Pacific Railroad (SPRR) and Leprino Foods is to the north, across East <br /> Grantline Road (Figure 2). <br /> The site is located about 3,500 feet south of Highway 205 at an elevation of <br /> approximately 30 feet above mean sea level (NGVD-1929). Topography in <br /> 'r the vicinity of the site is relatively flat, sloping slightly to the north. <br /> Regional Geology <br /> and Hydrogeology: The site lies in the Central Valley of California. Geologically, the valley is a <br /> large asymmetric trough that is bounded by pre-Tertiary granitic, metamorphic, <br /> and marine sedimentary rocks. The trough has been filled with as much as <br /> 30,000 feet of sediment in the San Joaquin Valley to the south and as much as <br /> 60,000 feet of sediment in the Sacramento Valley to the north. These <br /> sediments range in age from Jurassic to Holocene and include both marine and <br /> continental sedimentary deposits(USGS, 1986). <br /> This site investigation has included only the uppermost Tertiary and Quaternary <br /> age deposits. Lithologically these deposits are heterogeneous mixtures of <br /> poorly sorted clay, silt, sand, and gravel, and in places some beds of ciaystone, <br /> 1 <br />