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<br />[: (1",0 <br />U..;/."O <br /> <br />/3 <br /> <br />11 <br /> <br />top of the unweathered Pierre Shale would provide excellent informacion <br /> <br />regarding the depth of cutoff needed. <br /> <br />S. The pertl'le~i1ity of the sands and gravels in the lower <br /> <br />portion of the buried c.l-tannel see.'lLS unusually high. The sediments <br /> <br />~ediately above chese sands and gravels are apparently less permeable <br /> <br />but have not been tested directly for per.meability. These pe:meabilities <br /> <br />a=e some of the most critical factors in establishing both the safety <br /> <br />and the feasibility of the proposed daI!\. <br /> <br />6. Seismicity is quite low in the region of the dam site but <br /> <br />some dat3 should be provided to establish the degree of intensity that <br /> <br />may be anticipated. <br /> <br />CONCLUSImrs <br /> <br />1. Informacion available at presen~ is sufficient to establish <br /> <br />a preliminary design for the Narr~~s Dam. However, it should be noted <br /> <br />that the feasibility and safety of the dam are to a great extent <br /> <br />dependent on the &bility to control ~e passage of water around the <br /> <br />right abutment and to regulate the uplift pressures in this general <br /> <br />area. <br /> <br />2. 'l"ne cutoff tre...,ch under the embankment and the slurry <br /> <br />cutoff trend'1 will be effective only if t.'1.ey bottoI!:1 in unweathered <br /> <br />shale. <br /> <br />3. Pressure relief wells could provide a safe exit gradient for <br /> <br />groundwater. These wells should bottom in unweathered shale. <br /> <br />" <br />~- <br />