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L & M OPERABLE UNIT- FIRST QUARTER 2012 SITE STATUS, REMEDIAL SUMMARY, <br />AND GROUNDWATER MONITORING REPORT <br />Groundwater Monitoring and Sampling <br />April 30, 2012 <br />I:\Tidewater\TW Stockton (P2A)\QMRs\2012\1Q12\1Q12 QSSR QRSR QMR Stockton_FINAL.doc 2.16 <br />2.6 FIRST QUARTER 2012 D-ZONE GROUNDWATER RESULTS <br />2.6.1 D-Zone Groundwater Gradient Data <br />D-Zone groundwater elevations at the Site ranged from 5.95 ft below MSL in well MW-71 to <br />5.68 ft below MSL in wells MW-68 and MW-69 (Table 3 and Figure 24). Groundwater gradient <br />during 1Q12 in the D-Zone was calculated to the east-northeast with an approximate hydraulic <br />gradient of 0.0004 ft/ft (Figure 24). The highest D-Zone groundwater elevation (5.95 ft below <br />MSL) was reported in well MW-71, located in the northeast corner of the UOU. Historical <br />groundwater flow direction and gradient data are summarized in Table 8, and vertical gradients <br />summarized in Table 9. The D-Zone groundwater elevation contour map for the January 17, <br />2012 monitoring event is included as Figure 24. <br />2.6.2 D-Zone Groundwater Quality Data <br />During 1Q12, groundwater samples were collected from eight D-Zone wells between January <br />17 and 20, 2012 (Table 1). Groundwater analytical results are presented in Tables 4 through 7, <br />and summarized below. TPHg, TPHd, TPHo, benzene, MtBE, and TBA isoconcentration <br />contour maps are included as Figures 25 through 30, respectively. The certified laboratory <br />analytical reports for the groundwater sampling event conducted for the L&M OU are included in <br />Appendix D. <br />2.6.2.1 Separate Phase Hydrocarbons <br />During 1Q12, measurable SPH or SPH-sheen was not observed in any D-Zone wells. <br />2.6.2.2 Petroleum Hydrocarbons and Fuel Oxygenates <br />TPHg, TPHd, TPHo, and Fuel Oxygenates with concentrations at or above the MRLs are <br />summarized below.