ARCHIVED REPORTS SECOND SEMIANNUAL AND 2013 ANNUAL GROUNDWATER MONITORING REPORT

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3. Annual Report for 2013 This section presents the 2013 annual report and includes a summary of groundwater monitoring results, an evaluation of the effectiveness of the current remediation system, and an evaluation of potential data gaps and deficiencies/redundancies in the MRP. 3.1 Groundwater Monitoring Results Two semiannual groundwater monitoring events were performed for the 2013 monitoring period (October 2012 through September 2013) in accordance with MRP No. R5-2007-0831. The results from the first semiannual 2013 event were documented in a semiannual monitoring report submitted to the RWQCB on April 30, 2013 (CH2M HILL, 2013). The tables and figures that provide the tabular and graphical summaries of these data are presented in Appendix F. Results from the second semiannual 2013 event are documented in Section 2 of this report. • Table 2-Groundwater Depths and Elevations • Table 3 -Hydrocarbon Concentrations and Field Parameter Results • Figure 3- Groundwater Elevation Contour Map • Figure 4-Dissolved-Phase TPHg Concentration Map • Figure 5 -Dissolved-Phase Benzene Concentration Map These current data are also presented in Appendix C as part of the tabulation of the eight most recent quarters of collected data: • Table C.1 -Historical Groundwater Elevation Data • Table C.2-Historical Groundwater Concentration Data Appendix D provides a graphical summary (time-series charts) of the water level data and select chemical monitoring data since quarterly monitoring was implemented in 1992. A hydrograph is provided for all monitoring wells. Time-series concentration charts are provided for wells that have consistently detectable BTEX and TPH concentrations (wells ' 0-1,M-10,N-7,N-8, N-15, N-16,N-17,RW-1). Appendix E provides time-series concentration charts for these wells with the time scale expanded to 2050 to help assess potential long-term concentration trends. 3.1.1 Groundwater Elevations and Flow Average annual rainfall typically is approximately 13.6 inches per year as recorded by the City of Stockton rain gauge. Historically, during normal rainfall years, the water table increases during the spring semiannual event following the winter rainy period and then decreases during the fall semiannual event following the dry summer months,as shown in the hydrograph in Appendix D. The correlation between higher groundwater elevations during the winter and lower groundwater elevations after the summer has been observed since monitoring began in 1992. ' WBG101513183707SCOIHOLT_2SA13_REPORT FINAL 3-1