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Stantec <br /> L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2012 SITE STATUS, <br /> REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT <br /> Soil Vapor Sampling <br /> February 1, 2013 <br /> 4.2.2 APSV Soil Vapor Concentrations <br /> Soil vapor sampling data collected during 4Q12 sampling event is provided in Table 22 and <br /> shown on Figure 35. TPHg was detected in samples collected from APSV-9 and APSV-10 at <br /> concentrations of 44.0 and 139.4 parts per million by volume (ppmV), respectively. Methane <br /> was detected in samples collected from APSV-9 and APSV-10 at concentrations of 110,000 and <br /> 130,000 ppmV, respectively. No additional requested analytes were detected at or above the <br /> MRL in the APSV wells during 4Q12. <br /> 4.2.2.1 APSV Trends <br /> During 4Q12, TPHg concentrations increased in samples collected from APSV-9 and decreased <br /> in samples collected from APSV-10 in comparison to 3Q12 sampling event. During 4Q12, <br /> methane concentrations increased in samples collected from APSV-9 and APSV-10 in <br /> comparison to 3Q12 sampling event. All other sampled vapor points have been below the MRL <br /> for all requested analytes since fourth quarter 2010. Concentrations are shown in Table 22. <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 4Q12. This is <br /> consistent with the previous quarter (3Q12) data (Table 22, Figure 36 through 38). <br /> 4.2.3 UPSV Soil Vapor Concentrations <br /> Soil vapor sampling data collected during 4Q12 sampling event is provided in Table 22 and <br /> shown on Figure 35. TPHg and methane were detected in samples collected from UPSV-5 at <br /> concentration of 2,054 and 22,000 ppmV, respectively. No additional requested analytes were <br /> detected at or above the detection limits in the samples collected from the UPSV wells during <br /> 4Q12. There have been no fuel oxygenates detected in UPSV wells since their installation. <br /> 4.2.3.1 UPSV Trends <br /> During 4Q12, TPHg and methane concentrations increased in samples collected from UPSV-5 <br /> in comparison to 3Q12 sampling event. There were no detections of the requested analytes at <br /> or above the detection limits in the remaining samples collected from all UPSV wells. For 20 <br /> consecutive quarters (1Q08 through 4Q12), wells UPSV-1 and UPSV-6 have had no detections <br /> of the requested analytes at or above the detection limits. As shown in Table 22, TPHg has <br /> historically decreased in wells UPSV-1 and UPSV-6 since base line sampling in July 2005 and <br /> since start-up of the on-site remediation system on May 31, 2007. Additionally, benzene, <br /> ethylbenzene, and total xylenes have decreased to below detection limits which are <br /> complimentary to the decreasing trend of TPHg observed in well UPSV-6 (Figure 39). There <br /> have been no other apparent trends associated with reported concentrations in the UPSV wells. <br /> I:\Tidewater\TW Stockton(P2A)\QMRs\2012\4Q12-Ann ual\4Q12 and Annual QSSR QRSR QMR Stockton_FINAL.doc 4.2 <br />