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UST Closure Report Sharpe Defense Distribution Region West Lathrop,California Page 18 however, contained concentrations of the other parameters that were less than the method detection limits. TPH-D was detected in concentrations above the method detection level (1 mg/kg) in only three of the 19 samples collected from the excavation floor. The highest concentrations of 200 mg/kg was in the sample (1E) from the eastern end of UST #21, which contained diesel fuel. This sample also contained the highest concentration of TPH-G (61 mg/kg). Total lead was detected at relatively low concentrations that ranged generally from 4 to 11 mg/kg in 12 of the 19 soil samples collected from the UST excavation floor. One sample, T-4W, contained 22 mg/kg lead. Lead had concentrations less than the method detection limit in the remaining 7 samples. 5.2 UST Excavation Floor Groundwater Sample The groundwater sample collected from the base of the UST excavation, GW-1-P, contained very high concentrations of MTBE (450 µg/L) and trace to minor concentrations of TPH-G (0.2 mg/L), TPH-D (0.05 mg/L), benzene (7.1 µg/L), ethylbenzene (1.2 µg/L) and xylenes (49 gg/L). 5.3 UST Excavation Stockpiles Samples TPH-D was detected in concentrations greater than the method detection level of 1.0 mg/kg in 38 of the 46 samples collected from the soil removed from the UST excavation and stockpiled. They include four composites of 16 samples from stockpiles SPA and SPB, 22 samples collected later from stockpiles SPA and SPB, and the 20 samples collected from the composite stockpile SPD. The concentration of TPH-D ranged from 2.4 to 88 mg/kg in the samples from stockpile SPA and SPB, but generally 6 to 30 mg/kg. All the samples from stockpile SPD contained concentrations of TPH-D greater than the method detection limit. They ranged from 5 to 71 mg/kg, but generally 6 to 16 mg/kg TPH-D. The average concentration of TPH-D in all 46 samples analyzed was 14 mg/kg, assuming that samples with TPH-D concentrations less than the method detection limit contained 1 mg/kg TPH-D. It is interesting to note that the average concentration of TPH-D in the samples from stockpiles SPA and SPB is nearly the same as that in the samples from the composite stockpile SPD (14 mg/kg and 13 mg/kg, respectively). It is also interesting that the concentration of TPH-D was greater than the method detection limit in only three of the 19 soil samples collected from the floor of the UST excavation. TPH-G was detected in only one of the 46 stockpile samples analyzed: 5.4 mg/kg TPH-G in sample SPB-7. This sample was also only one of two stockpile samples containing detectable to ® high concentrations of ethylbenzene (300 µg/kg in SPB-7 and 6.7 gg/kg in SPA-4). Sample SPB-7 also contained high concentrations of toluene (180 µg/kg) and xylenes (2600 µg/kg). The concentration of MTBE, however, was less than the method detection limit in sample SPB-7. N:\PROJECTS\3546\Reports\3546 UST Closure Report Draft.doc March 24,1999