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UST Closure Report Sharpe Defense Distribution Region West Lathrop,California Page 19 MTBE was detected in concentrations greater than 10 gg/kg (detection limit) in 22 of the 42 soil samples from the excavation stockpile that were analyzed. In these, MTBE ranged from 13 to 210 gg/kg. However, the concentrations of MTBE were greater than method detection limits in 82% (18 of the 22) samples collected from stockpiles SPA and SPB, but only 20% (4 of the 20) samples from the stockpile SPD. This could be the result of the mixing and some degree of aeration that the soil underwent while transferring the soil from stockpiles SPA and SPB to SPD. The 20 samples from stockpile SPD were initially analyzed for the oxygenates by EPA Method 8020. The 7 samples with concentrations of MTBE above the method detection limit were reanalyzed for oxygenates by EPA Method 8260. These showed that EPA Method 8020 yielded `false positive' results for MTBE in three samples (SPD-3, SPD-10 and SPD-12). The concentration of MTBE ranged from 13 to 80 gg/kg in the 18 samples from stockpiles SPA and SPB in which it was detected. The 22 samples from the stockpile contained an average of 34 gg/kg MTBE, assuming that those with concentrations below the detection limit contained 10 gg/kg MTBE (i.e. the detection limit). The concentration of MTBE ranged from 14 to 210 gg/kg in the 4 samples from stockpile SPD in which MTBE was detected. The other parameters analyzed in the sample with 210 gg/kg MTBE were all below detection limit except TPH-D (9.2 mg/kg) and very high total lead (200 mg/kg). However, total lead was not detected in the other two samples with relatively high concentrations of MTBE (24 gg/kg in SPD-4 and 27 gg/kg in SPD-8). Concentrations of the other five oxygenate parameters analyzed in the samples from stockpiles SPA and SPB (ethanol, tertiary-butanol, DIPE, ETBE and TAME) were all less than the detection limits. Only the samples from stockpile SPD with concentrations of MTBE above the method detection limit of EPA Method 8020 were analyzed for oxygenates by EPA Method 8260. The concentrations of these five oxygenates were all below the method detection limit. 5.4 Product and Vapor Return Pipe Line Soil Samples The concentrations of MTBE were somewhat above the method detection limit of 10 gg/kg in three of the 11 samples collected from the floor of the trenches excavated to remove product and vapor return piping (PL- series, Figure 6). Two of the samples were from the site of the small dispenser west of the truck fill stand (12 and 23 gg/kg MTBE in PL-1 and PL-2, respectively). The third was from the south end of the truck fill stand, the site of overhead dispensers for gasoline and diesel fuel (sample PL-10 with 16 gg/kg MTBE). The concentrations of the other five oxygenates were below method detection limits in all 11 samples. TPH-D was detected in concentrations above the method detection limits in 7 of the 11 samples from the trenches. Concentrations of TPH-D in those samples ranged from 3.9 to 68 mg/kg. Only three of the samples were collected from the site of fuel dispensers; the other 4 from areas ® of 90° bends in the direction of product pipes. And only two of the 7 samples with detectable TPH-D also contained concentrations of MTBE greater than the method detection limits: PL-2 from the western product dispenser (25 gg/kg) and PL-11 from just northwest of UST #21 N:\PROJECTS\3546\Reports\3546 UST Closure Report Draft.doc March 24,1999