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r samples were composited 2:1 before analysis. Groundwater did not enter the excavation, and water samples were not collected. The samples were analyzed by EPA methods 8015m, 8020, and 8260 for Total Petroleum Hydrocarbons as gasoline, benzene, toluene, ethylbenzene, and xylene (BTEX), and five gasoline oxygenates (methyl tertiary butyl ether [MTBE], tertiary butanol [TBA.], di- isopropyl ether [DIPE], ethyl tertiary butyl ether [ETBE], and tertiary amyl methyl ether [TAME]). The samples from tank 43 were also analyzed for Total Petroleum Hydrocarbons as diesel, and all stockpile samples were analyzed for total lead at the request of the di3posal facility. No gasoline or diesel was reported in any of the excavation samples, but gasoline concentrations ranging from 14 to 49 mg/kg (parts per million) were reported in the stockpile samples. Benzene was detected in all stockpile samples at concentrations ranging from 0.009 to 0.37 ppm and in the middle and southern samples from tank 1 at concentrations of 0.008 and 0.015 ppm. Toluene and xylene were detected in the northern sample from tank 1, and xylene was also detected in the middle sample, at concentrations ranging from 0.007 to 0.012 ppm. Toluene and xylene were also detected in the stockpile samples. MTBE and/or its derivative TBA were detected in all of the stockpile samples, at concentrations ranging from 66 to 1900 ppm, and in all but one of the tank samples at concentrations ranging from 6.0 to 45 ppm. The results imply that most of the contamination was removed with the excavated soil, but low concentrations of the relatively less volatile components remain. 4.0 PROPOSED ASSESSMENT 4.1 Vertical Extent of Contamination The vertical extent of contamination will be delineated by drilling one soil boring near the center of the former tank cavity (Figure 2). The boring will be drilled with a hollow-stem auger drilling rig. Beginning at 20 feet (four feet below the previously collected tank samples), soil samples will be collected at 5-foot intervals and screened for evidence of petroleum with a portable photo-ionization detector or organic vapor meter, and v4ll be preserved for laboratory analysis. The minimum anticipated depth of the boring is 4+) feet, but drilling will continue until two consecutive samples exhibit no contamination. The estimated depth to groundwater is 55 feet, and if groundwater is reached before two consecutive uncontaminated soil samples have been collected, a well will be constructed in the boring. The well will use 2-inch-diameter PVC casing, following the design shown in Figure 3. After the well has stabilized, it will be purged of at least 5 well volumes of water, and a sample will be collected. Soil and water samples will be analyzed for gasoline, BTEX, and MTBE by EPA nicthods 8015, 602, and 8020. If MTBE is detected in any samples, the sample with the lowest concentration will be re-analyzed by method 8240B or 8260 to confirm the presence of MTBE.