2006-10-30_REVISION - M1988112 - Laserfiche WebLink

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As part of the revised plan, the South Diversion Channel will remain in place and continue to direct stormwater azound the reclaimed tailings surface. As a result, the only surface water inputs to the Tailings Disposal Area will be direct precipitation, runoff from the southern section of the reclaimed Mill Area, and runoff from the hill slope area to the north. This will result in a smaller spillway being needed to pass the design flow (associated with the 100-year, 24-hour storm) than was required under the original reclamation plan, where the South Diversion Channel was to be removed. The total acreage contributing surface water flows to the reclaimed impoundment under the revised plan is approximately 191 acres. The peak flow through the reclamation spillway during the 100-yr, 24-hr storm is estimated to be approximately 134 cubic feet per second (cfs). A preliminary design was prepared for the spillway to serve as the basis for the revised reclamation cost estimate. Water will be conveyed from the tailings surface to the existing stream channel downstream of the collection pond via a spillway channel. The spillway channel will consist of three segments as described below: I. A 1500-foot-long upper segment connecting the low-point of the reclaimed tailings surface (in the vicinity of the current 22.6-acre tailings pool) with the drop structure (segment 2) immediately downstream of tailings dam. This section of the channel will be constructed at a relatively flat bed slope (0.3 to 0.5 %), with a bottom width of 3 feet, side slopes of 3:1 (h:v) and a depth of 3.5 feet. The peak velocity in this segment will be approximately 3.75 feet per second (fps) during the design storm. Due to the relatively low peak velocity during the design storm, erosion protection armoring will not be needed in this segment. 2. A middle, drop-structure segment immediately downstream of the right abutment of the tailings embankment. The drop-structure segment will be approximately 540 fee[ long and constructed by excavating a channel in native soil and weathered rock forming the hill slope. This section will have a relatively steep bed slope (approximately 27%), with a finished bottom width of 3 feet, side slopes of 2:1(h;v), and a depth of approximately 1.5 feet. Due to the high velocities (up to 35 fps) associated with the design storm, erosion protection, consisting of a 6-inch thick concrete facing, will be required for [his segment. An additional assumption is that a 20-foot long by 6-foot wide stilling basin will be required at the downstream end of this segment. Battle Mountain Resources, /nc. 12 Telesto Solutions, /nc. P:WOjecu~213-Newmom(Smil.uis)\SanLUis\Pe,mu Amentlment- Wut Pit Mmugemem\V4 RCport &. PDFSWUmitAmeMment_v4.0oc October 2006