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<br />t <br /> <br />Woodward.Clyde Consultants <br /> <br />~ <br /> <br />lOGe <br /> <br /> <br />VII CONCLUSIONS <br /> <br /> <br />We have concluded that there are no indications of <br /> <br /> <br />geological structural features that present a risk to the <br /> <br /> <br />safety of the dam. The Pierre formation contains deposits of <br /> <br /> <br />gypsum which we believe should be investigated from a leaching <br /> <br /> <br />standpoint. We believe landslides in the reservoir to be a low <br /> <br /> <br />level risk. <br /> <br /> <br />Our independent analyses, using feasibility grade data <br /> <br /> <br />available to us, indicate that the downstream portion of the <br /> <br /> <br />maximum section of the darn, as proposed by the Bureau, is <br /> <br /> <br />reasonable from a safety standpoint under steady-state <br /> <br /> <br />reservoir conditions. In our opinion, some slumping of the <br /> <br /> <br />upstream section of the dam may occur under rapid drawdown <br /> <br /> <br />conditions if the low permeability and low cohesion material <br /> <br /> <br />presently proposed is used for the Zone 2 construction. We <br /> <br /> <br />believe the upstream slope should be redesigned for rapid <br /> <br /> <br />drawdown conditions giving full consideration to the type of <br /> <br /> <br />materials that can be developed from proposed or other <br /> <br /> <br />available borrow areas. In our opinion, the risk of earthquake <br />induced ground motions adversely affecting the stability of the <br />dam is low. <br />We believe a reasonably effective cutoff can be achieved <br />on the right abutment by the proposed combination of backfilled <br />trench and slurry trench, prov ided: (a) the slurry trench is <br />carried into competent pierre shale formation; (b) the trench <br /> <br />. <br /> <br />t <br /> <br />t <br /> <br />t <br /> <br />t <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />- 27 - <br /> <br />t <br /> <br />., <br />