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Stantec <br /> L & M OPERABLE UNIT- FOURTH QUARTER AND ANNUAL 2012 SITE STATUS, <br /> REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT <br /> Groundwater Monitoring and Sampling <br /> February 1, 2013 <br /> central portion of the site, groundwater flow direction was to the northeast with an approximate <br /> hydraulic gradient of 0.007 ft/ft. In the western part of the site, groundwater flow direction was <br /> to the north-northwest with an approximate hydraulic gradient of 0.009 ft/ft (Figure 10). The <br /> highest B-Zone groundwater elevation (1.28 ft above MSL) was reported in well MW-44, located <br /> in the southwest portion of the Site, east of Mormon Slough. The overall historic trend of the <br /> B-Zone gradient is to the east-northeast. Historical groundwater flow direction and gradient <br /> data are summarized in Table 5, and vertical gradients summarized in Table 6. The B-Zone <br /> groundwater elevation contour map for the October 15, 2012 monitoring event is included as <br /> Figure 10. <br /> 2.4.2 B-Zone Groundwater Quality Data <br /> During 4Q12, groundwater samples were collected from six deep zone wells between October <br /> 15 and 17, 2012 (Table 1). Groundwater analytical results are presented in Table 4, and <br /> summarized below. TPHg, TPHd, TPHo, benzene, MtBE, and TBA isoconcentration contour <br /> maps are included as Figures 11 through 16, respectively. The certified laboratory analytical <br /> reports for the groundwater sampling event conducted for the L&M OU are included in <br /> Appendix E. <br /> 2.4.2.1 Separate Phase Hydrocarbons <br /> During 4Q12, measurable SPH or SPH-sheen was observed in eight wells. SPH thicknesses <br /> for B-Zone wells are summarized below; "Sheen" indicates a SPH thickness of less than 0.1 <br /> inch. <br /> Well Identification SPH Thickness <br /> (feet) <br /> MW-17 Sheen <br /> MW-43 0.35 <br /> MW-46 Sheen <br /> MW-47 Sheen <br /> MW-48 Sheen <br /> MW-49 0.50 <br /> MW-50 30.70 <br /> MW-52 Sheen <br /> 2.4.2.2 Petroleum Hydrocarbons and Fuel Oxygenates <br /> TPHg, TPHd, TPHo, and Fuel Oxygenates with concentrations at or above the MRLs are <br /> summarized below. <br /> I:\Tidewater\TW Stockton(P2A)\QMRs\2012\4Q12-Ann ual\4Q12 and Annual QSSR QRSR QMR Stockton_FINAL.doc 2.6 <br />