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SUPPLEMENTAL SITE INVESTIGATION <br /> Former Mobil Oil Bulk Plant 04-343 <br /> i 500 East Grantline Road <br /> f Tracy, California <br /> i <br /> May 19, 1992 <br /> 1,0 INTRODUCTION AND BACKGROUND <br /> Alton Geoscience was retained by Mobil Oil Corporation to conduct a further supplemental <br /> site investigation at former Mobil Oil Bulk Plant 04-343, located at 500 East Grantline Road, <br /> Tracy, California. The site vicinity map is shown in Figure 1. <br /> This investigation was conducted to assess the nature and extent of hydrocarbons in the <br /> subsurface soil and ground water, particularly in the downgradient direction, thus addressing <br /> the concerns of the San Joaquin County Public Health Services (SJCPHS), as expressed in <br /> their letters of February 10 and April 17, 1992. Specific issues raised in the letter dated <br /> April 17, 1992, are addressed in Appendix A. <br /> 1.1 Site Description <br /> The site is presently a fenced, vacant lot. Adjacent properties are either vacant or <br /> commercial and industrial developments, as shown in Figure 2. The site is bounded by <br /> vacant lots to the east and south. Doane Product Company is located to the west, across the <br /> Southern Pacific Railroad. Residential property is located to the northwest, across the <br /> Southern Pacific Railroad and East Grantline Road. Leprino Foods is to the north, across <br /> East Grantline Road. <br /> The site is at an elevation of approximately 33 feet above mean sea level (msl), (NGVD- <br /> 1929), as shown in Figure 1. The average depth to ground water is approximately 11 feet <br /> below grade (fbg) or 21 feet msl. <br /> 1.2 Project Back round <br /> In August 1988, Mobil Oil Corporation abandoned the former bulk plant. All structures <br /> were removed from the property including one underground gasoline storage tank and four <br /> aboveground diesel fuel storage tanks, shown in Figure 2. Following removal of the <br /> underground tank, analysis of soil and ground water samples detected the presence of total <br /> petroleum hydrocarbons (TPH); and benzene, toluene, ethylbenzene, and total xylenes <br /> (BTEX). <br /> �� _ 1 <br />