ARCHIVED REPORTS_3RD QUARTER 2010 SITE STATUS REMEDIAL SUMMARY AND GROUNDWATER MONITORING REPORT

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Stantec ' L & M OPERABLE UNIT-THIRD QUARTER 2010 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Groundwater Monitoring and Sampling October 27, 2010 Because RPD was not run in the LCS for these analytes, precision could not be confirmed. ' However, since neither analyte was detected in site samples, during this event and historically, the reported values are not considered to be affected. tValidation issues with report number 73872: Matrix Spike and MSD results associated with sample MW-16 for the analyte MtBE were outside of the stated OC limits. This may indicate a possible bias for the reporting accuracy. ' The RPD values are within range indicating precision in reporting. The LCS recoveries were within OC limits indicating accuracy in reporting. Therefore, the reported values are considered valid. t2.5 THIRD QUARTER 2010 C-ZONE GROUNDWATER RESULTS ' 2.5.1 C-Zone Groundwater Gradient Data C-Zone groundwater elevations at the Site ranged from 7.21 ft below MSL in well MW-64 to ' 6.47 ft below MSL in well MW-65 (Table 3 and Figure 17). Groundwater flow direction during the third quarter 2010 was observed in two sections of the site (northeast and central). Along the northeastern portion of the site, groundwater flow direction was to the northeast with an approximate hydraulic gradient of 0.002 fUft. In the central part of the site, groundwater flow direction was to the northwest with an approximate hydraulic gradient of 0.002 ft/ft (Figure 17). Historical groundwater flow direction and gradient data are summarized in Table 8, and vertical ' gradients summarized in Table 9. The C-Zone groundwater elevation contour map for the July 19, 2010 monitoring event is included as Figure 17. ' 2.5.2 C-Zone Groundwater Quality Data During the third quarter 2010, groundwater samples were collected from eight C-Zone wells t between July 19 and 22, 2010 (Table 1). Groundwater analytical results are presented in Tables 4 through 7, and summarized below. TPHg, TPHd, TPHo, benzene, MtBE, and TBA isoconcentration contour maps are included as Figures 18 through 23, respectively. The ' certified laboratory analytical reports for the groundwater sampling event conducted for the L&M OU are included in Appendix C. ' 2.5.2.1 Separate Phase Hydrocarbons During the third quarter 2010, measurable SPH or SPH-sheen was not observed in any C-Zone ' wells. 2.5.2.2 Petroleum Hydrocarbons and Fuel Oxygenates TPHg, TPHd, TPHo, and Fuel Oxygenates with concentrations at or above the MRLs are summarized below. ' 19Tida teATW Stockton(Pan:e12A-NlS)\Reports\QMR1 010\3010\3010QSSRQRSRQMR Stackton_FINAL.doc 2.12