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<br />Woodward.CIyde Consultants <br /> <br />("'("'!r.{"l <br />'::",:JO <br /> <br />. <br /> <br />VII CONCLUSIONS <br /> <br />We have concluded that there are no indications of <br /> <br />geological structural features that present a risk to the <br /> <br />. <br /> <br />safety of the dam. The Pierre formation contains deposits of <br /> <br /> <br />gypsum which we believe should be inves)7i~ted from a leaching <br /> <br /> <br />standpoint. We believe landslides in th~rvoir to be a low <br /> <br /> <br />level risk. ,~~ <br /> <br /> <br />Our independent analyses, U~~g feasibility~grade data <br /> <br /> <br />available to us, indicate tha~~e downstream portion of the <br /> <br /> <br />maximum section of the dam, ~s~p6sed by the Bureau, is <br /> <br /> <br />reasonable from a safety standPoint;(nder steady-state <br /> <br /> <br />reservoir conditions. In our o~~some slumping of the <br /> <br /> <br />upstream section of th~-0c,cu~der rapid drawdown <br /> <br /> <br />conditions if the low perm~ik~~ low cohesion material <br /> <br /> <br />presently proposed is use~for~he Zone 2 construction. We <br /> <br /> <br />. believe the ups~~~ope S~~ld be redesigned for rapid <br /> <br /> <br />--- - -- -drawdown-con'd,i~v;:ug-~-;rr considef'aTion-fo-t::hetype-o-f----- -, ,- <br /> <br /> <br />materials th~can be developed from proposed or other <br /> <br /> <br />availab)7/60rrOW~~In our opinion, the risk of earthquake <br />induced 9~,tioons adversely affecting the stability of the <br />dam i~ <ow. J <br /> <br /> <br /> <br />~~ve a reasonably effective cutoff can be achieved <br /> <br /> <br />on the righ~butment by the proposed combination of backfilled <br /> <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />trench and slurry trench, prov ided: (a) the slurry trench is <br /> <br />. <br /> <br />carried into competent Pierre shale formation; (b) the trench <br /> <br />- 27 - <br /> <br />t <br /> <br />IA. <br />~ <br />