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Stantec <br /> L & M OPERABLE UNIT-THIRD QUARTER 2011 SITE STATUS, REMEDIAL SUMMARY, <br /> AND GROUNDWATER MONITORING REPORT <br /> Soil Vapor Sampling <br /> October 28, 2011 <br /> 4.2.2 APSV Soil Vapor Concentrations <br /> Soil vapor sampling data collected during 3Q11 sampling event is provided in Table 25 and <br /> shown on Figure 35. TPHg was detected in samples collected from APSV-9 and APSV-10 at <br /> concentrations of 20.0 and 102.7 parts per million by volume (ppmV), respectively. Methane <br /> was detected in samples collected from APSV-9 and APSV-10 at concentrations of 62,000 and <br /> 83,000 ppmV, respectively. No additional requested analytes were detected at or above the <br /> MRL in the APSV wells during 3Q11. <br /> 4.2.2.1 APSV Trends <br /> During 3Q11, TPHg concentrations increased in samples collected from APSV-10, and <br /> decreased in samples collected from APSV-9 in comparison to 2Q11 sampling event. During <br /> 3Q11, methane concentrations increased in samples collected from APSV-9 and APSV-10 in <br /> comparison to 2Q11. Concentrations are shown in Table 25 <br /> Except for wells APSV-9 and APSV-10, there were no detections of the requested analytes at or <br /> above the detection limits in the samples collected from the APSV wells during 3Q11. This is <br /> consistent with the previous quarter (2Q11) data (Table 25, Figure 36 through 38). <br /> 4.2.3 UPSV Soil Vapor Concentrations <br /> Soil vapor sampling data collected during 3Q11 sampling event is provided in Table 25 and <br /> shown on Figure 35. TPHg was detected in samples collected from UPSV-2, UPSV-3, and <br /> UPSV-5 at concentrations of 3.7, 17.1, and 1,638 ppmV, respectively. Methane was detected in <br /> samples collected from UPSV-3 at a concentration of 150,000 ppmV, respectively. No <br /> additional requested analytes were detected at or above the detection limits in the samples <br /> collected from the UPSV wells during 3Q11. There have been no fuel oxygenates detected in <br /> UPSV wells since their installation. <br /> 4.2.3.1 UPSV Trends <br /> During 3Q11, TPHg concentrations increased in samples collected from UPSV-3 in comparison <br /> to 2Q11 sampling event. TPHg concentrations were indeterminable for samples collected from <br /> UPSV-2 and UPSV-5 since both wells were not sampled during 2Q11. During 3Q11, methane <br /> concentrations increased in samples collected from UPSV-3 in comparison to 2Q11 sampling <br /> event. There were no detections of the requested analytes at or above the detection limits in <br /> the remaining samples collected from all UPSV wells. For fourteen consecutive quarters (1Q08 <br /> through 3Q11), wells UPSV-1 and UPSV-6 have had no detections of the requested analytes at <br /> or above the detection limits. As shown in Table 25, TPHg has historically decreased in wells <br /> UPSV-1 and UPSV-6 since base line sampling in July 2005 and since start-up of the on-site <br /> remediation system on May 31, 2007. Additionally, benzene, ethylbenzene, and total xylenes <br /> have decreased to below detection limits which are complimentary to the decreasing trend of <br /> I:\Tidewater\TW Stockton(P2A)\QMRs\2011\3Q11\3011 QSSR QRSR QMR Stockton_FINAL.doc 4.2 <br />