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Memorandum 2 February 9, 2010 <br />EPP Review Denison Mines <br />Addendum to the Hydrologic Evaluation <br />DRMS Comments/questions: <br />1 - Should the number in the last column of the last row of Table 1 be 1.96E+01 rather than 9.78E+00? <br />2 - Please provide a figure depicting the 3-dimensional nodal discretization of the UNSAT-H model. <br />3- The text states that the initial head was specified to be 1E-07 cm at all nodes, but the input file shows <br />1E+07 cm. Please explain. <br />4. A decrease in percolation with increasing precipitation is counter-intuitive, because of the increasing head <br />that should occur in the pile with increasing precipitation. Please describe the physical processes that occur <br />in the waste rock to cause percolation through the waste rock to decrease as precipitation increases, as <br />depicted on Figure 1 of the "Addendum to the Environmental Geochemistry Investigation of Soil and Rock <br />Materials, Sunday Mines Group." <br />Addendum to the Hydrologic Evaluation <br />Pg. 2: "it is hypothesized that the mine pool will return to the naturally more reducing conditions present <br />within the aquifer before significant migration of the mine pool occurs" and Pg.3: "Once mining ceases, <br />mine portals and ventilations shafts will be sealed to prevent ingress of oxygenated air into the underground <br />mine tunnels." <br />Response: DRMS agrees with the hypothesis regarding ground water flow and re-equilibration of the mine <br />pool water, but this will depend upon the successful exclusion of oxygenated air from the underground <br />workings. Please provide detailed specifications of the proposed mine seals, and a post-mining monitoring <br />program to ensure success.