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Stantec <br /> L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2010 SITE STATUS, <br /> REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT <br /> Groundwater Monitoring and Sampling <br /> January 31, 2011 <br /> MS/MSD results associated with samples MW-24, MW-26, MW-29, MW-32, MW-35, MW-44, <br /> MW-51, and QCDUP-2 for the analyte MtBE were outside of the stated QC limits for percent <br /> recovery. This may indicate a possible bias for the reporting accuracy. The RPD values are <br /> within range indicating precision in reporting. The LCS percent recoveries were within QC limits <br /> indicating accuracy in reporting; therefore, the reported values are considered valid. <br /> 2.5 FOURTH QUARTER 2010 C-ZONE GROUNDWATER RESULTS <br /> 2.5.1 C-Zone Groundwater Gradient Data <br /> C-Zone groundwater elevations at the Site ranged from 8.58 ft below MSL in well MW-54 to <br /> 7.05 ft below MSL in well MW-65 (Table 3 and Figure 17). Groundwater flow direction during <br /> 4Q10 was to the northwest with an approximate hydraulic gradient of 0.005 ft/ft (Figure 17). <br /> Historical groundwater flow direction and gradient data are summarized in Table 8, and vertical <br /> gradients summarized in Table 9. The C-Zone groundwater elevation contour map for the <br /> October 18, 2010 monitoring event is included as Figure 17. <br /> 2.5.2 C-Zone Groundwater Quality Data <br /> During 4Q10, groundwater samples were collected from eight C-Zone wells between October <br /> 18 and 21, 2010 (Table 1). Groundwater analytical results are presented in Tables 4 through 7, <br /> and summarized below. TPHg, TPHd, TPHo, benzene, MtBE, and TBA isoconcentration <br /> contour maps are included as Figures 18 through 23, respectively. The certified laboratory <br /> analytical reports for the groundwater sampling event conducted for the L&M OU are included in <br /> Appendix C. <br /> 2.5.2.1 Separate Phase Hydrocarbons <br /> During 4Q10, measurable SPH or SPH-sheen was not observed in any C-Zone wells. <br /> I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual OSSRQRSRQMR Stockton_FINAL.doc 2.11 <br />