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2012 Annual Groundwater Monitoring and Evaluation Report <br /> Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation <br /> Former Marley Cooling Tower Site, Stockton,California February 2013 <br /> moved south in response to a gradient of approximately 0.0004 ft/ft in July 2012 and south in <br /> response to a gradient of approximately 0.0003 ft/ft in October 2012, as calculated between wells <br /> TW-13 and MW-310. The average linear velocity of groundwater in the 100-Foot Sand Zone <br /> was estimated using: <br /> • A hydraulic conductivity of 269.1 ft/day, which was averaged from hydraulic <br /> conductivities estimated from aquifer tests conducted at wells MW-310, MW-410, <br /> MW-411, and S-3 (H+A, 1989a and 1989b) <br /> • An effective porosity of 20 percent (H+A, 1990) <br /> • The hydraulic gradient calculated between wells TW-13 and MW-310 <br /> The average linear velocity of groundwater in the 100-Foot Sand Zone across the source area <br /> was approximately 0.57 ft/day in July 2012 and 0.38 ft/day in October 2012. <br /> 3.2.3 Intermediate Zone <br /> Potentiometric surface maps of Intermediate Zone groundwater for the first and second quarters <br /> of 2012 are presented in Appendix A (Figures 2, 3, 6 and 7). In July 2012, groundwater <br /> elevations ranged from—21.06 ft msl at MW-211 to -23.38 ft msl at MW-325. In October 2012, <br /> groundwater elevations ranged from -22.21 ft msl at EW-3 to -62.42 ft msl at MW-213 (I-7). <br /> Note that the MW-213 (1-7) measurement represents the pumping water level within the well, <br /> and that the water level in the aquifer adjacent to the well will be higher because of well losses. <br /> Groundwater in the Intermediate Zone across the source area moved south to southwest in <br /> response to a gradient of approximately 0.0007 ft/ft in July 2012 and 0.0003 ft/ft in October <br /> 2012, as calculated between wells MW-211 and MW-322. The average linear velocity of <br /> groundwater in the Intermediate Zone was estimated using: <br /> • A hydraulic conductivity of 85.3 ft/day, which was averaged from hydraulic <br /> conductivities estimated from aquifer tests conducted at wells 1-7, 1-8, MW-211, <br /> MW-320, and MW-212 (H+A, 1989a and 1989b) <br /> • An effective porosity of 7 percent (H+A, 1990) <br /> • The hydraulic gradient calculated between wells MW-211 and MW-322 <br /> (D MWH., <br /> 3-5 <br />