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3 <br /> Supplementary Site Assessment Report <br /> 1 Former Mobil Bulk Plant 04-343 <br /> April 26, 1996 <br /> 1.0 INTRODUCTION <br /> ' This report presents the findings of a site investigation performed at former Mobil Bulk Plant 04- <br /> 343, located at 500 East Grantline Road, in Tracy, California (Figure 1). The work was <br /> performed in accordance with the San Joaquin County Public Health Services, Environmental <br /> ' Health Division(PHS/EHD)requirements(Site Code: 1968)and the Alton Geoscience work plan <br /> dated November 14, 1994. The workplan was submitted to the PHSIEHD for review and <br /> approval to proceed was received from the PHSIEHD on January 10, 1995. <br /> The objective of this investigation was to further characterize residual soil contamination to the <br /> west of the site, which may remain after the 1990 remedial excavation(Alton Geoscience, 1990), <br /> ' and collect field data to assess the potential for enhanced biodegradation of hydrocarbon-affected <br /> soil and groundwater. <br /> ' 2.0 SITE DESCRIPTION <br /> Site Status: The site is currently a fenced-in vacant lot (Figure 2). The site was <br /> formerly a bulk fuel distribution facility operated by Mobil Oil <br /> Corporation. Plant operations were discontinued in 1988. All structures <br /> were removed from the property including one underground gasoline <br /> ' storage tank and four aboveground diesel fuel storage tanks. The site is <br /> bound by vacant lots to the east and south. Doane Products Company is <br /> ' located to the west, across the Southern Pacific Railroad (SPRR) and <br /> Leprino Foods is to the north, across East Grandine Road (Figure 2). <br /> The site is located about 3,500 feet south of Highway 205 at an elevation <br /> ' of approximately 30 feet above mean sea level (NGVD-1929). <br /> Topography in the vicinity of the site is relatively flat, sloping slightly to <br /> ' the north. <br /> Regional Geology <br /> and Hydrogeology: The site lies in the Central Valley of California. Geologically, the valley <br /> is a large asymmetric trough that is bounded by pre-Tertiary granitic, <br /> metamorphic, and marine sedimentary rocks. The trough has been filled <br /> ' with as much as 30,000 feet of sediment in the San Joaquin Valley to the <br /> south and as much as 60,000 feet of sediment in the Sacramento Valley to <br /> the north. These sediments range in age from Jurassic to Holocene and <br /> include both marine and continental sedimentary deposits (USGS 1986). <br /> i <br /> 1 <br />