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Both wells MW-34 and MW-36 are located off site and down gradient of well MW-20. <br /> These wells delineate the plume's down-gradient extent. <br /> 3.5.3 CROSS-GRADIENT WELLS <br /> Wells MW-18, MW-32, and MW-33 are used to verify concentration trends cross <br /> gradient of the site. Well MW-18 is cross gradient and east of the well MW-1 (truck <br /> loading rack) source area. As shown on the graphs for well MW-18 (C-7 and C-8),TPHd <br /> and TPHg concentrations are stable to decreasing, and benzene is typically not <br /> detected (0.91 µg/l, during the third quarter 2011). MTBE is not a constituent of concern <br /> for this well. TBA concentrations are increasing, ranging from 11 to 56 µg/l, since 2001. <br /> Well MW-18 also contained DIPE, with stable to increasing concentrations trends. <br /> Well MW-32 is located off site, cross gradient (east-southeast) of the well <br /> MW-10 (Tank 14) source area and east of wells MW-29 and MW-30. It delineates the <br /> plume's cross-gradient extent east of the site. Occasionally TPHd is detected in this well, <br /> and during the third quarter 2011, it contained 160 µg/L. <br /> Well MW-33 is located cross gradient and west of the well MW-1 source area. As shown <br /> on the graph for well MW-33 (C-9), the TPHd, TPHg, and benzene concentrations are <br /> decreasing. MTBE and TBA are not constituents of concern in this well. <br /> 3.5.4 UP-GRADIENT WELLS <br /> Wells MW-9 and MW-19 are used to verify concentration trends up gradient of the site. <br /> With the exception of the periodic low-level TPHd detections in both wells and <br /> low-level MTBE detections in well MW-9, these wells do not contain petroleum <br /> constituents and are sampled annually. Well MW-9 contained 26 µg/l,MTBE, and well <br /> MW-19 contained 6.1 µg/l,benzene during the third quarter 2011. <br /> 3.5.5 DEEPER WATER-BEARING ZONE WELL <br /> Well DW-2 is used to verify concentration trends down gradient and within a deeper <br /> water-bearing zone. During the third quarter 2011, 460 µg/l,TPHd, 20 µg/l, TBA, and <br /> 4.7 µg/l, DIPE were detected. The laboratory noted that the TPHd was partly due to <br /> individual peak(s) in the quantitation range. <br /> 241725(32) 6 CONESTOGA-ROVERS&ASSOCIATES <br />