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2011 Semiannual Groundwater Monitoring and Evaluation Report <br /> Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation <br /> Former Marley Cooling Tower Site, Stockton,California January 2012 <br /> groundwater elevations ranged from -13.84 ft msl at TW-16 to -24.78 ft msl at EW-1. <br /> Groundwater in the 100-Foot Sand Zone across the source area moved south in response to a <br /> gradient of approximately 0.0009 ft/ft in July 2011 and south in response to a gradient of <br /> approximately 0.0008 ft/ft in October 2011, as calculated between wells TW-13 and MW-310. <br /> The average linear velocity of groundwater in the 100-Foot Sand Zone 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 1.16 ft/day in July 2011 and 1.13 ft/day in October 2011. <br /> 3.2.3 Intermediate Zone <br /> Potentiometric surface maps of Shallow Zone groundwater for the third and fourth quarters of <br /> 2011 are presented in Appendix A (Figures 2 and 4). In July 2011, groundwater elevations <br /> ranged from —14.85 ft msl at MW-441 to -52.47 ft msl at MW-321 (1-9), which is an active <br /> extraction well. In October 2011, groundwater elevations ranged from -19.88 ft msl at MW-441 <br /> to -49.32 ft msl at MW-321 (I-9), which is an active extraction well. Groundwater in the <br /> Intermediate Zone across the source area moved south to southwest in response to a gradient of <br /> approximately 0.003 ft/ft in July 2011 and 0.00 18 ft/ft in October 2011, as calculated between <br /> wells MW-211 and MW-322. The average linear velocity of groundwater in the Intermediate <br /> 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 I-7, I-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 /> The average linear velocity of groundwater in the Intermediate Zone across the source area was <br /> approximately 3.8 ft/day in July 2011 and 2.3 ft/day in October 2011. <br /> (a MWH <br /> 3-5 <br />