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1; <br /> 1.0 INTRODUMON 3 <br /> The following report presents the findings of a soil and goundwater investigation 1 <br /> performed b Pacific En ' <br /> Y vtronnlental Group, Inc. (PACIFIC) at UNOCAI, Bulk <br /> Plant 0788, located at 8203 East 11th Street in Tracy, California (Figure 1). Three <br /> ,groundwater monitoring wells designated U-4, U-5, and U-6, and three exploratory.soil <br /> borings designated U-A, U-B, and U-C,were installed on site on May 9,1991,to forth r <br /> l evaluate the extent of petroleum hydrocarbons in the soil an4 groundwater underlying <br /> the site. This report presents site background information, a regional geologic and 3 <br /> hydrogeologic overview, sample collection and analytical procedures, findings, and <br /> {! recommendations. <br /> to <br /> 1.1 Background <br /> The site referenced above is an operating bulk <br /> p plant with two 19,500-gallon and <br /> two 20,000-gallon above-ground hydrocarbon storage tanks located in the western <br /> portion of the property (Figure 2). The 19,500-gallon tanks contain diesel and super a . <br /> unleaded gasoline; and the 20,000--Da tanks contain regular leaded gasoline and <br /> unleaded gasoline. According to sire personnel, then: tanks were installed in 1918 to ! <br /> replace the tanks originally installed during construction of the facility. A water supply <br /> well, designated WSW-1 is Iocated near the eastern property boundary. <br /> oun - <br /> According to site personnel, a leak occurred hi the underground piping between:the. <br /> above-ground storage tanks, and. the loading`rack during 1975 and, 1976.: In 1976, <br /> hydrocarbons were noted during underground construction in the Southern Pacific <br /> iw right-of-way to the north of the site. <br /> A partially buried 5,000-gallon tanl-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 ?0. 1990. Soil <br /> +-a samples were collected from the eastern and western ends of the tank excavation during <br /> --- ------ --tank-removal-acrivities,-at-a--depth-of-8 feer-below;late - boratorv-analysis of these <br /> f ' samples indicated the presence of 17 parts per million <br /> (ppm) diesel, 12 ppm toluene, <br /> �. <br /> and 4.9 ppm ethylbenzene in the eastern end of the excavation. The transmission fluid <br /> i <br /> 3100101;REPOR `' <br /> 1 Septcmer 30. 1991 <br /> v ., <br />