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<br />Crown Jewel Project <br />June 25, 1992 <br />Page 9 <br />SUMMARY <br />n <br />U <br />Mr. East acknowledged during the course of our June 11, meeting that [he <br />success or failure of this scheme hinges on the ability of the deposition <br />process to achieve an unsaturated state in the slimes shortly after their <br />emplacement. Failure to do so could resul[ in a static embankment failure due <br />to a buildup of water pressure in the pore fluid or conceivably a <br />liquefaction, "flow type" failure in the event a large earthquake. <br />The DSS believes that the likelihood is low that an unsaturated state can be <br />achieved uniformly in the slimes within the zone critical to the integrity of <br />the impounding barrier. The placement scheme may be capable of achieving the <br />desired state in the slimes under ideal conditions. However, during the <br />adverse weather of the winter months, it is the opinion of the DSS that the <br />controlled discharge scheme can not achieve uniformly an unsaturated state <br />within distances crucial to the integrity of the primary dam. The DSS <br />acknowledges that Knigh[ Piesold Company's proposal includes an ambitious <br />program to attempt to confirm through field testing that unsaturated <br />conditions have indeed been achieved in the impoundment. However, as a <br />practical matter the volume of slimes that would be tested would still be <br />minuscule. Thus, predictions made upon such data would not provide the level <br />of assurance necessary for a projec[ of this nature. <br />Based on the preceding comments the DSS sees no compelling arguments for <br />accepting an upstream embankment constzuction scheme. Obviously it: affords <br />the owner the most cost-effective containment scheme. But it does so by <br />posing what the DSS believes to be an undue risk of failure. Cive7~ that there <br />are conventional embankment schemes that effectively make an embanlment <br />failure acceptably remote, it would be imprudent to accept the Knif;ht Piesold <br />proposal. <br />If you wish to discuss this matter further, please call our office at (206) <br />459-6726. <br />Sincerely, <br />~~ 5`-~~- <br />Melvin G. Schaefer, Ph.D, P.E. <br />Supervisor, Dam Safety Section <br />Water Resources Program <br />/ Jerald LaVassar, P.E. <br />Dam Safety Section <br />Water Resources Pr~~gram <br />JL:MCS:dkh <br />Enclosure <br />cc: Donald East, Knight Piesold <br />Anne Baldrige, Golder Associates <br />Craig Stiles, Battle Mountain Gold Co. <br />Robert Raforth, Ecology <br />Patricia Crumley, Ecology <br />