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<br />8 <br /> <br />determining if piping will occur. <br /> <br />2. I concur with their recommendation that pressure relief <br /> <br />wells could provide a safe exit gradient. The wells should bottom in <br /> <br />good Pierre Shale. <br /> <br />3. Since there is not a detailed description of the ~HO- and <br /> <br />three-dimensional models in the Memorandum, it is difficult to judge <br /> <br />the predictive capability of the models used. <br /> <br />4. I concur with the recommendation that a three-dimensional <br /> <br />model be used to determine the beneficial effects of the cutoff wall <br /> <br />operating simultaneously with pressure relief wells. <br /> <br />5. The permeability values in the lower alluvial sands and <br /> <br />gravels are quite high. These should be checked. If the values were <br /> <br />lower, the hydraulic gradient in ~'e buried channel would be higher, <br /> <br />resulting in greater uplift pressure. <br /> <br />A Memorandum by the U.S. Bureau of Reclamation on the subject <br /> <br />"Permeability Testing/Narrows Dam/Narrows Unit/Pick-Sloan Missouri <br /> <br />Basin Program" arrived on December 23, 1977. This is a preliminary <br /> <br />report giving conclusions based on an aquifer (pump out) test and ten <br /> <br />permeability (pump in) tests. The results of these investigations <br /> <br />provide a better data base for determining the probable behavior of <br /> <br />groundwater in the south bank of the river when the reservoir is <br /> <br />raised to its ultimate height. The results of these latest studies <br /> <br />correspond quite well with ~'e studies by the U.S. Geological Survey <br />