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I. ''_ Aga sure I III I II I II I II IIII III <br />_ a ,. • a <br />~ F • 999 - <br />Yn <br />0 <br />.. 1 leer ~ <br />STATE OF WASHINGTON <br />DEPARTMENT OF ECOLOGY <br />Mail 5(op PV-77 • Olympia, Washhgton 98504711 • (1Q5) 459~i000 <br />November 6, 1992 <br />Mr. A. Walter Wise F <br />Battle Mountain Gold Company ~ " ~~~' RECEAU EQ <br />42nd Floor ,199 <br />333 Clay Street ~~C+ 1 ~0~ 16 1992. <br />Houston, Texas 77002 p1\I bl ., , <br />PROJECT: Crown Jewel Project 1~1~NEPALS ~ ~~-' ga'ttlc . _ JU~ <br />Ecsibn~ <br />FILE NO.: OK60-625 <br />Dear Mr. Wise: <br />This letter outlines the position of the Dam Safety Section (DSS; on the use <br />of the centerline and upstream embankment construction schemes proposed by <br />Knight Pidsold. The DSS position is as follows. <br />As stated in previous correspondence, the DSS can approve a centerline <br />embankment scheme for the upper portion of the main dam. <br />The DSS could also approve a centerline scheme for the upper Fortion of the <br />embankment that includes an upstream construction scheme optic n, provided <br />certain conditions are met. Specifically, the Knight Pi~sold method of <br />upstream construction could be substituted for the portion of the <br />embankment placed by the centerline method. The Knight PiAsold method of <br />upstream construction is a variant on traditional upstream methods and <br />reportedly addresses many of the static and seismic stability concerns of <br />this emplacement method. Our approval of the modified upstream <br />construction option would be contingent upon demonstrating that appropriate <br />performance criteria have been achieved. <br />BACKGROUND <br />In June 1992, representatives of Knight Pi€sold met with the DSS to discuss <br />their preliminary plans for two embankments that will impound process slimes. <br />The proposed scheme involved constructing the upper stages of the larger of <br />the two embankments over the dewatered slimes. Specifically, in this upstream <br />phase of construction, the discharge area immediately upstream of the <br />embankment would be divided into a series of subbasins. The discharge of <br />slimes would be cycled or rotated among these subbasins so as to deposit a <br />thin lift of slimes in each subbasin. Further discharge to a given subbasin <br />would be delayed to allow a specified degree of water loss to occur. <br />During the meeting, the DSS raised a number of concerns regarding the ability <br />of the process to satisfactorily dewater the slimes during the wet season. <br />Failure to maintain the slimes in an unsaturated state would pose concerns for <br />the static and seismic stability of the main embankment. The DSS followed up <br />that meeting with a June 25, 1992, letter that rejected the Knight Pi€sold <br />~" o'S <br />