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SC&D Boyett Petroleum October 23, 1998 <br /> 419 South Main Street, Manteca, California Page 4 <br /> Underground Storage Tank Preliminary Investigation -ROF <br /> • Groundwater contamination in the form of MTBE is present at concentrations <br /> of 6,700 to 47,000 ug/L. <br /> Wim' finds the results of this scope of work disturbing in light of the fact that considerable <br /> MTBE contamination was found only at a depth of sixteen (16) feet and below. The <br /> entire column of soil was "ND" except those areas where the soils were saturated with <br /> groundwater. This fact leads VdW to believe that the MTBE contamination problem is <br /> waterborne, and is from an off site source. <br /> During the previous upgrade activities in 1996, the excavation extended to a maximum <br /> depth of 2.5 feet and soil samples were taken at twenty-four (24) inches b.g.l. (Figure 4). <br /> The soil samples showed concentrations of MTBE between 340 and 740 ug/Kg (Table 4). <br /> Below this depth, virgin soil is encountered and it would stand to reason that if the source <br /> of the MTBE contamination was on site, it would be found in soil samples from the <br /> surface to sixteen (16) feet b.g.l. This is not the case. MTBE is not present in the soil <br /> samples from four (4) to at least eleven (11) feet b.g.l. MTBE is only found in the soil <br /> samples at sixteen feet, which is in the capillary fringe. <br /> Also, the concentrations of MTBE, as shown by the laboratory results in 1996, are <br /> relatively low compared to those now found in the soil only at sixteen (16) feet and the <br /> groundwater at eighteen (18) feet. This fact further strengthens VHF's conclusion that the <br /> sources of this problem may be from an offsite location. <br /> The original sampling of the stockpile occurred on November 21, 1996. The laboratory <br /> analysis for this sampling event showed levels of MTBE at 1,100 ug/Kg, Toluene between <br /> 5.7 and 11.0 ug/Kg, Ethyl Benzene between 4.6 and 7.6 ug/Kg, Xylene between 35 and <br /> 59 ug/Kg, and Gasoline between 2.7 and 4.4 mg/Kg. The laboratory analyses that were <br /> performed on the October 5, 1998 sampling event on the stockpile indicated that all <br /> analytes tested, Gasoline, BTX&E, and MTBE, were"ND". Therefore, the stockpiled <br /> soils will be disposed off site and used as fill material. <br /> 1 <br /> 1 <br />