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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 /> 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 C). <br /> Validation issues with report number 75022: <br /> Matrix Spike (MS) and Matrix Spike Duplicate (MSD) results associated with samples <br /> QCEB-1-RG and QCTB-1 for the analytes MtBE and TBA were outside of the stated QC limits <br /> for percent recovery. This may indicate a possible bias for the reporting accuracy. The relative <br /> percent difference (RPD) values for MtBE and TBA are within range indicating precision in <br /> reporting. The laboratory control sample (LCS) percent recoveries were within QC limits, for the <br /> analytes MtBE and TBA, indicating accuracy in reporting; therefore, the reported values are <br /> considered valid. <br /> MS/MSD results associated with samples MW-23, MW-25, MW-30, MW-33, MW-34, and <br /> MW-45 for the analyte MtBE were outside of the stated QC limits for percent recovery. This <br /> may indicate a possible bias for the reporting accuracy. The RPD values are within range <br /> indicating precision in reporting. The LCS percent recoveries were within QC limits indicating <br /> accuracy in reporting; therefore, the reported values are considered valid. <br /> 2.4 FOURTH QUARTER 2010 B-ZONE GROUNDWATER RESULTS <br /> 2.4.1 B-Zone Groundwater Gradient <br /> B-Zone groundwater elevations at the Site ranged from 7.59 ft below MSL in well MW-35 to <br /> 0.88 ft above MSL in well MW-44 (Table 3 and Figure 10). Groundwater flow during 4Q10 in <br /> deeper zone (B-zone) was noticed in four separate sections of the site (northeast, southeast, <br /> central, and west). The highest B-Zone groundwater elevation (0.88 ft above MSL) was <br /> reported in well MW-44, located in the southwest portion of the site east of Mormon Slough. <br /> Along the northeastern portion of the Site, groundwater flow direction was to the southeast with <br /> an approximate hydraulic gradient of 0.02 ft/ft. In the southeastern portion of the Site, <br /> groundwater flow direction was to the east-southeast with an approximate hydraulic gradient of <br /> 0.004 ft/ft. In the central part of the site, groundwater flow direction was to the northeast with an <br /> approximate hydraulic gradient of 0.006 ft/ft. In the western portion of the Site, groundwater <br /> flow direction was to the north-northwest with an approximate hydraulic gradient of 0.009 ft/ft <br /> (Figure 10). The overall historic trend of the B-Zone gradient is to the east-northeast. Historical <br /> groundwater flow direction and gradient data are summarized in Table 8, and vertical gradients <br /> summarized in Table 9. The B-Zone groundwater elevation contour map for the October 18, <br /> 2010 monitoring event is included as Figure 10. <br /> I:\Tidewater\TW Stockton(Parcel 2A-0415)\Reports\QMR\2010\4010-Annual\4Q10 and Annual OSSRQRSRQMR Stockton_FINAL.doc 2.7 <br />