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i ii iiiiiiiiiiiuiii .~ <br /> <br /> STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />pF.~~( <br /> <br />Department o(Natural Resources O <br />.,~~: r <br /> ~~ ~ o <br />1313 Sherman St., Room 215 • <br />(~ . <br />Denver, CO 80:03 • <br />~ • <br />• <br />Phone: 13031 866-3567 ie~b <br />FA%:(3031832-8106 <br />Roy Romer <br /> Governor <br />MEMORANDUM <br />Glic hael e. Long <br />=' Division Dnecror <br />J _. <br />October 1, 1992 ' <br />TO: B. Humphri s,,,,L. Oehler, J. Pendleton, A. Sorenson <br />FROM: H. Posey ,~J <br />RE: Tailings am Design; Battle Mountain Gold; Crown Jewel <br />Project; Washington State. File with BMG; San Luis <br />Project; Permit No. M-88-112 <br />Battle Mountain Gold is currently attempting to permit ~t large vat <br />leach facility, the Crown Jewel Project, in the state of <br />Washington. Because BMG is a principal in both operations, and <br />because of similarities in processing methodologies between the <br />Crown Jewel and the San Luis Projects, the DMG ha:a received <br />periodic inquiries from individuals and agencies with an interest <br />in our perspective on both the company and the project. <br />Attached to this memo is a report from the Washington DeF~artment of <br />Ecology's Dam Safety Section (DSS) that rejects BMG': tailings <br />embankment design. The report outlines the DSS's logic for <br />rejecting that design, the key points of which are: <br />1. Dams constructed using the Upstream Construction design <br />have failed in several parts of the world once subjected <br />to earthquake stresses. Failure was due to liquefaction <br />of the tailings beneath that portion of the dam that was <br />built upon wet tailings. Notable locations of dam <br />failures include Japan and Chile. (Incidentally, Japan <br />and Chile are in the Pacific earthquake ring where <br />earthquakes occur very frequently.) <br />Successful employment of the Upstream Construction method <br />depends on dewatering the tailings lifts. ~ewatering <br />cannot occur either when the tailings are frozen or when <br />they are loaded in thick lifts. Dewatering verification <br />is operator dependant. <br />Variations in pore fluid content between tailings layers <br />could lead to static slope failure. In other words, it <br />would not necessarily take an earthquake to trigger slope <br />failure. <br />The reason this item may concern the DMG is that the Crown Jewel <br />tailings impoundment design is similar to the San Luis design. In <br />