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In addition, four discrete soil samples were collected for analysis from the waste soil stockpiles. Three of the four soil stockpile samples contained detectable concentrations of TPH-as-gasoline, toluene, ethylbenzene, and xylenes. MTBE was only detected in one of the four soil stockpile samples. 1.2.2 Preliminary Investigation and Evaluation The objectives of the preliminary investigation were to further define the extent of impacted soil and to determine if groundwater had been impacted beneath the site. To achieve these objectives, soil and groundwater-grab samples were collected for laboratory analysis from three on-site Geoprobe soil borings (Figure 2). w Soils observed in the three borings consisted of a massive clay and silt sequence overlying a discontinuous silty fine sand interval of undetermined thickness. During drilling, groundwater was ` first encountered at depths ranging from 14.2 to 15.0 feet below ground surface (bgs). Ground surface is approximately 12 feet below street grade. Groundwater did not appear to be confined and recharge was moderately strong. Results of the investigation indicated that soil and groundwater beneath the site had been impacted by gasoline hydrocarbons. In soil, the sample collected at 15 feet from B-2, near the south end of former UST contained the highest concentrations: 400 milligrams per kilogram (mg/kg) of TPH-as-gasoline, 0.3 mg/kg of benzene, 5.9 mg/kg of toluene, 11 mg/kg of ethylbenzene, 43 mg/kg of xylenes, 0.065 mg/kg of MTBE, and 9.5 mg/kg of total lead. In groundwater, the sample collected from B-2 contained the highest concentrations: 36,000 �. micrograms per liter (µg/l) of TPH-as-gasoline, 1,700 gg/I of benzene, 4,600 4g/I of toluene, 1,400 µg/I of ethylbenzene, 5,900 µg/I of xylenes, and 25 µg/I of MTBE. The soil sample analytical +— results are summarized in Table 1, and the groundwater analytical results are included in Table 2. Based on the distribution of gasoline hydrocarbons in soil and groundwater, the primary source of 4. the impacts appears to be the former gasoline UST. The bulk of the hydrocarbon mass is concentrated in soil and groundwater beneath the south end of former UST. Vertically, the extent of impacted soil is mostly delineated but not completely defined at the total drilling depth of 20 feet bgs. Laterally, the extent of impacted soil is defined to the south by B-1 and mostly delineated to the north by B-3. The extent of impacted groundwater at the groundwater table is only defined to �. the north by B-3. Concentrations of gasoline hydrocarbons in groundwater appear to.decline significantly to the south at B-1. 5 w