ARCHIVED REPORTS SECOND SEMIANNUAL AND 2013 ANNUAL GROUNDWATER MONITORING REPORT

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3.ANNUAL REPORT FOR 2013 Overall,the concentrations of BTEX and TPH constituents began to increase after extraction stopped from well N-17 in February 2004. This likely occurred because clean, downgradient groundwater was no longer being pulled into the capture zone (and into wells N-16 and N-17) to dilute the BTEX and TPH constituents that were being pulled downgradient from the source area. Since the initial concentration increases after the extraction was shut down, ' a new equilibrium appears to have been established where the naturally occurring processes are resulting in decreasing concentrations for the BTEX and TPH constituents. 3.2 Effectiveness of the Current Remediation System The current remediation system consists of MNA and the phytoremediation system, as summarized in Section 1. The combination of these two strategies is effective,resulting in a sitewide decline in TPH and BTEX concentrations in groundwater and a stable-to-shrinking extent of these constituents in groundwater. As discussed with the RWQCB during meetings on July 12,2007, and September 21, 2007,and reflected in the current MRP issued by the RWQCB, the steady reduction in hydrocarbon mass,as well as reductions in BTEX ' and TPH concentrations,at the Site are the result of fate-and-transport processes occurring naturally in the subsurface. These naturally occurring processes are documented in the Final Site Characterization Report(CH2M HILL,2002) and in the 3-Year Evaluation of the Bioremediation Pilot Study(CH2M HILL,2007a). The steady reduction in hydrocarbon mass is shown in the time-series concentration charts in Appendix D and Appendix E. i 3.3 Identification of Data Gaps and Potential Deficiencies/ Redundancies No data gaps or deficiencies have been identified. Routine groundwater monitoring at the Site was implemented in March 1992. To date, the groundwater monitoring program has been performed for approximately 21 years and has provided important time-series information with respect to groundwater elevations and gradients, NAPH thicknesses, and chemical concentrations in groundwater and surface water. Seasonal patterns in groundwater elevation fluctuations,as well as seasonal and long-term trends in BTEX and TPH concentrations,have been identified, as documented in the Final Site Characterization Report (CH2M HILL, 2002) and in subsequent routine groundwater monitoring reports. Robust data have been collected to demonstrate that the naturally occurring processes are sufficient to result in a continued declining trend of these hydrocarbon constituents without the active remediation systems, as documented in the 3-Year Evaluation of the Bioremediation Pilot Study(CH2M HILL,2007a). No redundancies have been identified regarding the wells that are sampled and analytes that are analyzed in the laboratory. Current MRP No. R5-2007-0831 was developed to be streamlined to monitor current Site conditions with MNA and phytoremediation as remedies. This MRP eliminated most of the parameters added in the previous MRP to monitor the bioremediation pilot test,eliminated unnecessary monitoring wells and parameters,allowed for the destruction of unnecessary monitoring wells, and allowed for the destruction of the soil vapor extraction well system. ' WBG101513183707SCO/HOLT_2SA13_REPORT_FINAL 3-3