ARCHIVED REPORTS_SECOND SEMIANNUAL AND 2011 ANNUAL GROUNDWATER MONITORING REPORT

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L 3.ANNUAL REPORT FOR 2011 • SFPP compared the HydraSleeve sample results to the conventional standard purge sampling data for the second semiannual 2011 sampling event and to long-term concentration data available since 1992. This comparison is discussed in Section 3.4.2. • If the HydraSleeve results are comparable,SFPP would propose to use only HydraSleeve sampling going forward,upon final approval by the RWQCB. 3.4.1 HydraSleeve Results As described in Section 2,HydraSleeve samples were collected from seven monitoring wells 1r (half of the normal number sampled) during the second semiannual sampling event on September 1, 2011.Seven monitoring wells were chosen that capture the range of conditions at the Site (low-to-high concentrations,coarse versus fine-grained lithology, shallow versus deep),and include the following monitoring wells:N-7,N-8,N-15,N-16, N-19,N-24 and RW-1. Analytical results comparing the HydraSleeve sample data to the standard purge Lsample data are presented in Table 4. On a per-analyte basis,HydraSleeve concentration is plotted versus standard purge concentration in Figure 6,for wells that had detectable BTEX and TPH concentration values for both sampling methods. Nondetected values were not plotted on the graphs;if one well had a detect via HydraSleeve and a nondetect via standard purge, the concentrations were excluded from the graph.The concentrations were plotted on a logarithmic axis,and linear regression"R2" values for each BTEX and TPH constituent are provided.The linear regression values by analyte across all the wells are high,ranging from 0.8015 (for TPHg) to j 0.9986 (for toluene),which indicate a strong fit between the data for the two types of sampling methods for concentrations that were detected,on a sitewide basis (Figure 6). Figure 7 presents a similar plot of the hydrocarbon concentrations by well and illustrates a statistical"good fit" between the two methods for the wells (with detectable BTEX and TPH concentrations) that were sampled for both methods at the site. L BTEX and TPH constituent concentrations from the two methods (HydraSleeve and standard purge) are the most consistent amongst monitoring wells located on the plume fringe (N-8),downgradient of the plume (N-19),and in deeper well N-24. Downgradient monitoring well N-19 had all non-detect concentration for BTEX and TPH constituents for the two sampling methods; deeper well N-24 had all non-detect values for the two sampling >w methods,except for anomalous concentrations of TPHd (0.53 mg/L) and benzene (2.7 gg/L) found in the standard purge sampling results.BTEX and TPH constituent data from the two sampling methods from wells located within the former release area(N-7 and N-8) and at 1r former extraction well RW-1,is within the same order of magnitude,and is thus moderately i consistent among the two methods. In addition,hydrocarbon concentrations from the ` HydraSleeve data fall within long term concentration trends for monitoring data available since 1992 on a site wide basis (Appendix D). The HydraSleeve concentrations are plotted along with the historical data in Appendix D (for wells with detects). (+� 3.4.2 Conclusions and Recommendations BTEX and TPH constituent data collected by two sampling methodologies,standard purge sampling and HydraSleeve, displayed comparable results and a statistical "good fit' among the seven wells that were sampled at the site,on a sitewide basis. SFPP and CH2M HILL propose to use only HydraSleeve sampling going forward, upon approval by the RWQCB. 4 ES1024111833088COILW3521.000X/112970003 3-5 Lr