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2013 Semiannual Groundwater Monitoring and Evaluation Report <br /> Full-Scale In Situ Hexavalent Chromium Reduction Treatment Implementation <br /> Former Marley Cooling Tower Site,Stockton,California August 2013 <br /> • The hydraulic gradient calculated between wells MW-210 and MW-9 <br /> The average linear velocity of groundwater in the Shallow Zone across the source area was <br /> approximately 0.0 15 ft/day in January 2013 and 0.022 ft/day in April 2013. <br /> 3.2.2 100-Foot Sand Zone <br /> In January 2013, groundwater elevations ranged from -21.67 ft msl at MW-310 to -21.99 ft msl <br /> at TW-15 and TW-16. In April 2013, groundwater elevations ranged from -22.24 ft msl at MW- <br /> 310 to -22.48 ft msl at TW-15. Groundwater in the 100-Foot Sand Zone across the source area <br /> moved south in response to a gradient of approximately 0.00007 ft/ft in January 2013 and 0.0001 <br /> ft/ft in April 2013 as calculated between wells TW-13 and MW-310. The average linear velocity <br /> 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-l3 and MW-310 <br /> The average linear velocity of groundwater in the 100-Foot Sand Zone across the source area <br /> was approximately 0.009 ft/day in January 2013 and 0.14 ft/day in April 2013. <br /> 3.2.3 Intermediate Zone <br /> Potentiometric surface maps of Intermediate Zone groundwater for the first and second quarters <br /> of 2013 are presented in Appendix A (Figures 2, 3, 5 and 6). In January 2013, groundwater <br /> elevations ranged from —21.85 ft msl at MW-450D to -61.14 ft msl at I-11. In April 2013, <br /> groundwater elevations ranged from -21.76 ft msl at MW-441 to -61.60 ft msl at I-11. Note that <br /> the 1-11 measurement represents the pumping water level within the well, and that the water <br /> level in the aquifer adjacent to the well will be higher because of well losses. Groundwater in <br /> the Intermediate Zone across the source area moved south to southwest in response to a gradient <br /> of approximately 0.0003 ft/ft in January 2013 and 0.00036 ft/ft in April 2013, as calculated <br /> between wells MW-211 and MW-322. Note that the first quarter 2013 groundwater elevations at <br /> Q) MW <br /> 3-5 <br />