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i, <br /> The soil sample collected at 25 feet bgs from SB-10, northeast of the UST excavation, contained <br /> the highest concentration of MTBE (0.25 mg/kg). MTBE was detected in 13 of the 38 soil <br /> samples analyzed and TBA was detected in six of the 38 samples. Only the soil sample <br /> t <br /> collected at 15 feet bgs from SB-10 contained detectable concentrations of methanol (0.42 <br /> mg/kg) and ethanol (0.063 mg/kg). The oxygenate compounds, DIPE, ETBE, and TAME were <br /> not detected in any of the 38 soil samples analyzed. <br /> t , <br /> Vertically, the extent of impacted soil beneath the site was defined in six of the 11 soil borings. <br /> In the other five soil borings, MTBE was detected in the deepest samples, at a maximum depth <br /> of 35 feet bgs. TBA was detected in two of the deepest samples (S135-25 and SB10-25) and <br /> toluene and xylenes were detected in one of the deepest soil samples (SB6-35). <br /> Laterally, the majority of the petroleum hydrocarbon mass in soil is concentrated at <br /> Fapproximately 25 feet bgs. An isoconcentration map of TPH-as-gasoline in soil at 25 feet is <br /> -- shown on Figure 3. The concentrations of MTBE detected in the deeper soil samples (25 to 35 <br /> feet bgs) are present in the northeastern and northern portions of the site. <br /> 3.2.2 Groundwater Sample Results <br /> The groundwater samples from all 11 of the soil borings contained a detectable concentration of <br /> at least one of the compounds analyzed. Only the groundwater sample collected from the on- <br /> F site domestic well was free of detectable concentrations of TPH-as-gasoline, BTEX and <br /> oxygenate compounds. <br /> F <br /> TPH-as-gasoline was detected in groundwater from eight of the 11 soil borings. The highest <br /> concentration of TPH-as-gasoline was detected in SB-6, north of the dispensers, at a <br /> concentration of 62,000 micrograms per liter (µg/1). The distribution of TPH-as-gasoline in <br /> groundwater is depicted in Figure 4. The isoconcentration map shows that the lateral extent of <br /> TPH-as-gasoline in groundwater appears to be defined on the south side of the site and <br /> undefined on the north side of the site. ' <br /> The highest concentrations of BTEX compounds in groundwater were also detected in SB-6. In <br /> SB-6, benzene was detected at 230 µg11, toluene at 8,100 µg1l, ethylbenzene at 3,000 µg11, and <br /> fill xylenes at 21,000 µg/l. <br /> MTBE was detected in the groundwater samples from ten of the 11 soil borings. The maximum <br /> concentration of MTBE was detected at SB-10, northeast of the UST excavation, at 9,600 µg11. <br /> r 13 <br />