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{ INTRODUCTION f The following re resents the findings of a soil and groundwater investigation g P ort P sperformed by Pacific Environmental Group, Inc. (PACIFIC) at UNOCAL Bulk Plant l No.0788 located at 8203 East 11th Street in Tracy, Califo-is (Photos 1 &2 and Figure 1). Three groundwater monitoring wells were installed on October 24 and 25, R R 1990, to.evaluate the extent of petroleum hydrocarbons in the soil and groundwater in 4 the vicinity of a subsurface 5,000-gallon transmission fluid tank recently removed from i e the site. This report presents site background information, a .regional geologic and hydrologic overview, sample collection and analytical procedures, findings, and 1 recommendations- 1 Background 4 The above referenced site is an operating bulk plant with two 19,500-gallon and r 'carbon storage tanks located in the western two 20,000-gallon above ground hydro !'moi portion of th,; property (Figure 2). The 19,500-gallon tanks contain diesel and super Yom✓ unleaded gasi'.ine, and the 20,000-gallon tanks contain regular leaded gasoline and unleaded gasoli=ne. According to site personnel, these tanks were installed in 1918 to ! replace the tanks originally installed during construction of the facility. A partially buried 5,000-gallon tank was removed from the southwestern portion of the site on December 13, 1989. The primary use of this tank was for transmission fluid storage,but it has also been used to contain heating oil in the past.: Details of the exca- vation of this tank are described in a PACIFIC letter to UNOCAL dated March 20, 1990. Soil samples were collected from the eastern and western ends of the tank exca- vation at a depth of 8 feet below ground surface during tank removal activities. Cervi- fled laboratory analysis of these samples indicated the presence of 17 parts per million (ppm)diesel, 12 ppm toluene,and 4.9 ppm ethylbenzene in the eastern end of the exca= vation.,The transmission fluid tank resided on an underground concrete pad,which.was not removed during excavation. Groundwater was observed in the excavation at a depth of 6 feet below surface during the December 1989 tank removal activity: i t i I 1 February 13,1991 3100101/REPORT . x 1 r