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Mr. Alec Schatz <br />April 13, 2006 <br />Page 3 <br />the Rising Sun ditch as it approaches Pit III. Based on the results with the Pit I runs, it seems <br />likely that rechazging water to the ditch vicinities could alleviate much of the drawdown effects. <br />However, the question arises as to whether the dewatering process for the respective pits will <br />generate enough water to handle the mitigation in all locations required. The results of the Pit I <br />analyses indicate that this may be a significant issue. <br />Of concern with the results of this modeling exercise is the fact that very high rates of <br />pumping are predicted to effectively dewater the pit areas. Predicted rates in excess of 35,000 <br />gpm could be difficult and potentially expensive to establish and sustain. <br />An alternative to the dewatering as simulated in the model would be to consider <br />installation of slurry walls around the pits. This would avoid the need for the ongoing high <br />dewatering pumping rates and would allow for far easier control of the wetland areas. In <br />addition, there would be essentially no impacts on the Colorado River if slurry walls were <br />installed and the initial dewatering were pumped directly back to the river. The costs of such <br />slurry wall lining would need to be weighed against the dewatering costs to determine if such a <br />plan were economically feasible. <br />Please let us know if you have any questions concerning these latest model simulations of <br />the contents of this letter. <br />Sincerely, <br />hppe .Martin, C.P.G. <br />Vice President <br />Martin and Wood Water Consultants, Inc. <br />