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1.0 INTRODUCTION <br /> �- The following report presents the findings of a soil and groundwater investigation <br /> performed by Pacific Environmental Group, Inc. (PACIFIC) at UNOCAL Bulk <br /> Plant 0788, located at 8203 East 11th Street in Tracy, California (Figure 1). Four <br /> groundwater monitoring wells designated U-7, U-8, U-9, and U-10 were installed on <br /> March 10 through March 12, 1992, to further evaluate the extent of petroleum <br /> hydrocarbons in the soil and groundwater underlying the site. Groundwater Monitoring <br /> Wells U-7 and U-8 were installed on-site, and Wells U-9 and U-10 were installed on <br /> private property immediately west of the site (Figure 2). This report presents site <br /> background information, a regional geologic and hydrogeologic overview, the scope of <br /> work, procedures for the work performed, a discussion of the findings, and <br /> recommendations. <br /> 1.1 Background <br /> The site is an operating bulk plant with two 19,500-gallon and two 20,000-gallon above- <br /> ground hydrocarbon storage tanks located in the western portion of the property <br /> (Figure 2). The 19,500-gallon tanks contain diesel and super unleaded gasoline, and the <br /> 20,000-gallon tanks contain regular leaded gasoline and unleaded gasoline. According <br /> to site personnel, these tanks were installed in 1918 to replace the above-ground tanks <br /> originally installed during construction of the facility. A water-supply well, designated <br /> WSW-1, is located near the eastern property boundary and is used for non-potable <br /> sanitation purposes. <br /> According to site personnel, a release occurred from the underground piping between <br /> the above-ground storage tanks and the loading rack sometime during 1976 and was <br /> subsequently repaired. In 1976, separate-phase hydrocarbons were noted during <br /> underground construction in the Southern Pacific right-of-way to the north of the site. <br /> A partially buried 5,000-gallon tank was removed from the southwestern portion of the <br /> site on December 13, 1989. The tank was primarily used for transmission fluid storage, <br /> but it had also been used to contain heating oil in the past. Details of the excavation of <br /> this tank are described in a PACIFIC letter to UNOCAL dated March 20, 1990. Soil <br /> samples were collected from the eastern and western ends of the tank excavation during <br /> 3100103/REPORT3 1 June 11, 1992 <br />