ARCHIVED REPORTS SECOND SEMIANNUAL AND 2013 ANNUAL GROUNDWATER MONITORING REPORT

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3.ANNUAL REPORT FOR 2013 , As shown in Figure 3 of this report and Figure 3 in Appendix F, groundwater flow patterns ' were consistent for the March 12, 2013,and September 13, 2013, 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 NAPH was not detected in any of the groundwater monitoring wells in 2013. NAPH has not , been detected at the site since 2002. 3.1.3 BTEX and TPH , Except for an anomalous detection of benzene at well N-18,BTEX and TPH constituents were not detected in the shallow upgradient monitoring well (M-1) or shallow downgradient wells (M-8, N-19, and N-20) during the first and second semiannual sampling events in 2013,which is consistent with the historical monitoring results. BTEX and TPH constituents also were not detected in the deeper well (N-24) during the first and second , semiannual events in 2013. Benzene was detected at a low concentration(1.9 µg/L) in well N-18 during the first semiannual event in 2013. The detection of benzene is considered anomalous because BTEX constituents historically have not been detected in this well before 2010. These recent detection of benzene and other BTEX constituents since 2010 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 in the 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 (wells 0-1, M-10,and N-8) and for the wells with higher concentrations located in the former release ' (source) area (wells N-7 and N-15). All these wells historically had NAPH,which is no longer detectable. The long-term ' concentrations for former extraction well RW-1 have exhibited a decreasing trend since monitoring for this well began in 2005. The decreases in wells M-10 and 0-1 have occurred to such an extent that well 0-1 is almost no longer in the hydrocarbon plume and well M-10 ' is now almost outside the plume. Before the start of the bioremediation pilot test,no long-term BTEX and TPH concentration trends for extraction well N-17 and nearby monitoring well N-16 were apparent. This potentially was due to extraction at well N-17 pulling hydrocarbons downgradient from the areas of higher contamination near the source area,which sustained the hydrocarbon concentrations. Since the start of the bioremediation pilot test in February 2004,the concentrations in wells N-16 and N-17 have shown similar behavior. 3-2 WBG101513183707SCOMOLT 2SA13_REPORT_FINAL '