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Stantec <br /> L & M OPERABLE UNIT-THIRD QUARTER 2011 SITE STATUS, REMEDIAL SUMMARY, <br /> AND GROUNDWATER MONITORING REPORT <br /> Groundwater Monitoring and Sampling <br /> October 28, 2011 <br /> 2.3.2.7 General Laboratory Notes <br /> The following validation issues are consistent with the shallow zone quality assurance and <br /> quality control. Each set of issues corresponds directly with the denoted report (Appendix D). <br /> Validation issues with report number 78182: <br /> Groundwater samples collected from well 2AMW-12 was analyzed by EPA Method 8260B using <br /> bottles that contained headspace bubbles greater than '/4 inch in diameter. <br /> Validation issues with report number 78189: <br /> The MRL for 1,1,2-trichloroethane and chloroethane were raised in samples collected from well <br /> MW-18 due to the presence of an interfering compound. <br /> The MRL for chloromethane was raised in samples collected from well MW-18 due to the <br /> presence of an interfering compound. <br /> Groundwater samples collected from wells QCTB and QCEB-2-RG were analyzed by EPA <br /> Method 8260B using bottles that contained headspace bubbles greater than '/4 inch in diameter. <br /> Validation issues with report number 78203: <br /> The MRL for 1,1,2-trichloroethane was raised in samples collected from well MW-9 due to the <br /> presence of an interfering compound. <br /> Groundwater samples collected from wells MW-9 and QCTB-3 were analyzed by EPA Method <br /> 8260B using bottles that contained headspace bubbles greater than % inch in diameter. <br /> 2.4 THIRD QUARTER 2011 B-ZONE GROUNDWATER RESULTS <br /> 2.4.1 B-Zone Groundwater Gradient <br /> B-Zone groundwater elevations at the Site ranged from 5.53 ft below MSL in well MW-50 to <br /> 3.07 ft above MSL in well MW-44 (Table 3 and Figure 10). Groundwater gradient during 3Q11 <br /> in the B-Zone was calculated to the northeast with an approximate hydraulic gradient of <br /> 0.009 ft/ft (Figure 10). The highest B-Zone groundwater elevation (3.07 ft above MSL) was <br /> reported in well MW-44, located in the southwest portion of the site east of Mormon Slough. <br /> The overall historic trend of the B-Zone gradient is to the east-northeast. Historical groundwater <br /> flow direction and gradient data are summarized in Table 8, and vertical gradients summarized <br /> in Table 9. The B-Zone groundwater elevation contour map for the July 18, 2011 monitoring <br /> event is included as Figure 10. <br /> I:\Tidewater\TW Stockton(P2A)\QMRs\2011\3Q11\3011 QSSR QRSR QMR Stockton_FINAL.doc 2.7 <br />