ARCHIVED REPORTS_SECOND SEMIANNUAL AND 2011 ANNUAL GROUNDWATER MONITORING REPORT

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r 3.ANNUAL REPORT FOR 2011 3.1.1 Groundwater Elevations and Flow As shown in the hydrograph in Appendix D,groundwater elevations increased during the first semiannual 2011 event(March 2,2011) during the winter rainy period and then J decreased during the second semiannual 2011 event(September 1,2011) after the summer dry period. The correlation between higher groundwater elevations during the winter and J lower groundwater elevations after the summer is consistent with the historical data collected since monitoring began in 1992. _ As shown in Figure 3 of this report and Figure 3 in Appendix F, groundwater flow patterns 1 were consistent for the March 2,2011,and September 1,2011 data. These groundwater flow patterns are also consistent with flow patterns from historical monitoring events before and after the active remediation systems (GWETS and SVETS)were shut down in February 2004 for the 3-year bioremediation pilot study.Groundwater flow is described in Section 2 above. 3.1.2 NAPH J NAPH was not detected in any of the groundwater monitoring wells in 2011.NAPH has not been detected at the site since 2002. 3.1.3 BTEX and TPH _ BTEX and TPH constituents were not detected in the shallow upgradient monitoring well J (M-1)or shallow downgradient wells (M-8,N-19, and N-20) during the first and second semiannual sampling events in 2011,which is consistent with the historical monitoring - I results. BTEX was not detected in well M-10 during the first and second semiannual sampling events in 2011,which is consistent with the historical decrease in concentrations in this well. BTEX and TPH constituents also were not detected in the deeper well (N-24) during the first semiannual event in 2011, except for anomalous low concentrations of TPHd (0.53 mg/L) and benzene (2.7 gg/L) detected during the second semiannual event in 2011. BTEX and TPH were detected at low concentrations in well N-18 during the first and second semiannual events in 2011.Well N-18 was resampled following the first and second — semiannual events,and BTEX and TPH were detected at similar low concentrations during resampling.The detections in these samples are considered anomalous because TPH and J BTEX constituents have not historically been detected in this well. These detections may be attributed to offsite sources, which include farm buildings in the immediate vicinity of this well. Well N-18 is being monitored to further evaluate the concentrations. BTEX and TPH constituents continue to be detected in the remaining monitoring wells, which are located in the former release area (wells N-7 and N-15),on the plume fringe (wells 0-1,N-8,and N-16),and former extraction wells (RW-1 and N-17).As shown in the time-series concentration charts in Appendix D, since the start of the bioremediation pilot test, the long-term BTEX and TPH concentration trends have continued to decrease significantly for the wells with lower concentrations located on the plume fringe (0-1,M-10, and N-8) and the wells with higher concentrations located in the former release (source) area (wells N-7 and N-15). f All these wells historically had NAPH,which is no longer detectable. The long-term J concentrations for former extraction well RW-1 have exhibited a decreasing trend since i 3.2 ESI 02411163306SCO/LW3521.DOCR/112970003