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. ~ J' ! <br />'• I / I I 1 <br />~T 4TE OF \V 4~HINGT0N <br />DEPARTMENT OF ECOLOGY <br />C lad iron PV- J f • C5: mora. lt.vshineton ~Ni0a-N: f f • /:Cbl 1'~-hIXXI <br />June 25, 1992 <br />Mr. A. Walter Wfse JUN Z 6 <br />Battle Mountain Gold Company <br />42nd Floor <br />333 Clay Street <br />Houston, Texas 77002 - <br />PROJECT: Crown Jewel Project <br />FILE NO.: OK60-625 <br />Dear Mr. Wise: <br />~ J' .L <br />This letter states the position of the Dam Safety Section (DSS) on Knight <br />Pi~sold and Company's proposal to employ an "upstream embankment construction" <br />scheme for the upper half of the 280 feet high primary dam, <br />To summarize, the DSS can not accept the proposal to employ this method of <br />construction for the embankment. Furthermore, it would be our preference to <br />allow only impounding barriers that are constructed in thin lifts and <br />systematically compacted to a dense unyielding state as in the tom entional <br />downstream construction approach. However, the DSS will consider a <br />"centerline embankment construction" scheme, if it can be demonstr~.ted that <br />the embankment will remain stable under static and dynamic loading. The <br />remainder of this letter summarizes the proposed scheme and the rationale for <br />rejecting the upstream dam construction proposal. <br />Most of the following comments were presented and discussed with Mr. Stiles of <br />the owner's staff, and the engineering consultants Messrs. East anti Lansdown <br />and Ms. Baldrige in a meeting at the DSS offices on June 11, 1992. <br />DESCRIPTION OF UPSTREAM CONSTRUCTION PROPOSAL <br />Embanl~ent Scheme - A valley will be dammed at either end to store the process <br />waste. Figure 1 presents a cross-sectional view of the larger of the two <br />dams, the 280 feet high primary dam, The lower half of the primar~~ embankment <br />and the entire 80 feet high, secondary embankment are to be constructed as <br />conventional zoned engineered fills, The remainder of the primary embankment <br />would be constructed in stages over the impounded slimes. Thus, tl~e <br />engineered fill section of the primary embankment along_with the adjacent zone <br />of deposited slimes would form a composite retaining structure. T~> facilitate <br />drainage of the slimes, an underdrain system would be extend along the <br />upstream face of the embankment and along the underside and upstream edge of <br />each of the upstream embankment stages. The underdrain discharge ~~ill be <br />collected and reused to make up process water. To minimize the in ..°iltration <br />of seepage into the embankment, a geomembrane would underlie the urtdetdrains <br />on the engineered fill section of the primary dam and the entire face of the <br />°~' a <br />