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 Validation issues with report number 73872: Matrix Spike and MSD results associated with samples MW -9 and MW -20 for the analyte MtBE ether were outside of the stated QC 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 QC limits indicating accuracy in reporting. Therefore, the reported values are considered valid. 2.4 THIRD QUARTER 2010 B -ZONE GROUNDWATER RESULTS 2.4.1 B -Zone Groundwater Gradient B -Zone groundwater elevations at the Site ranged from 7.19 ft below MSL in well MW -35 to 2.04 ft above MSL in well MW -44 (Table 3 and Figure 10). Groundwater flow during the third quarter 2010 in deeper zone (B -zone) was noticed in four separate sections of the site (northeast, southeast, central, and west). The highest B -Zone groundwater elevation (2.04 ft above MSL) was reported in well MW -44, located in the southwest portion of the site east of Mormon Slough. Along the northeastern portion of the Site, groundwater flow direction was to the southeast with an approximate hydraulic gradient of 0.02 ft/ft. In the southeastern portion of the Site, groundwater flow direction was to the east-southeast with an approximate hydraulic gradient of 0.005 ft/ft. In the central part of the site, groundwater flow direction was to the northeast with an approximate hydraulic gradient of 0.01 ft/ft. In the western portion of the Site, groundwater flow direction was to the north-northwest with an approximate hydraulic gradient of 0.01 ft/ft (Figure 10). The overall historic trend of the B -Zone gradient is to the east-northeast. Historical groundwater flow direction and gradient data are summarized in Table 8, and vertical gradients summarized in Table 9. The B -Zone groundwater elevation contour map for the July 19, 2010 monitoring event is included as Figure 10. 2.4.2 B -Zone Groundwater Quality Data During the third quarter 2010, groundwater samples were collected from 15 deep zone wells 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 11 through 16, respectively. The certified laboratory analytical reports for the groundwater sampling event conducted for the L&M OU are included in Appendix C. I:\Tidewater\TW Stockton (Parcel 2A-0415)\Reports\QMR\2010\3010\3010QSSRORSROMR Stockton_FINAL.doc 2.8