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As has been described, stormwater will be conveyed from the TDA surface to the <br />existing stream channel downstream of the collection pond via an open-channel <br />spillway. The spillway will consist of three segments as described: <br />1. A 1500-foot-long upper segment connecting the low-point of the <br />reclaimed TDA surface (in the vicinity of the current 22.6-acre tailings <br />pool) with the drop structure (segment 2) immediately downstream of <br />TDA. The upstream portion of this first segment will be an outlet- <br />controlled backwater, with flow controlled by a six-foot, concrete weir <br />with a Cipolletti-type geometry constructed at the northwest abutment of <br />the tailings dam. This upstream portion of segment 1 will be constructed <br />with a bottom width of 8 feet, side slopes of 2:1 (h:v), and a maximum <br />depth of 8 feet. The flow rate and peak velocity through the upstream <br />portion of this segment will be controlled by the weir. Due to the low <br />peak velocity during the extreme event (less than 4 feet per second), <br />erosion protection armoring will not be needed upstream of the weir. The <br />portion of the first segment lying downstream of the weir will be <br />constructed at a relatively flat bed slope (0.2%), with a bottom width of 8 <br />feet, side slopes of 2:1 (h:v) and a maximum depth of 6 feet. The peak <br />velocity in this segment will be approximately 4 feet per second (fps) <br />during the extreme storm event. Due to the low peak velocity during the <br />extreme event, erosion protection armoring will not be needed in this <br />segment. <br />2. A middle, drop-structure segment immediately downstream of the <br />northwest abutment of the tailings embankment. The drop-structure <br />segment will be approximately 540 feet long and constructed by <br />excavating a channel in native soil and weathered rock forming the hill <br />slope. This section will have a relatively steep bed slope (approximately <br />22%), with a finished bottom width of 3 feet, side slopes of 2:1 &v), and a <br />finished depth of approximately 3.5 feet. Due to the high velocities (up to <br />18 fps) associated with the design storm, erosion protection, consisting of <br />an energy-dissipating roughened concrete or grouted rip-rap facing, will <br />be constructed for this segment. A stilling basin consisting of a <br />rectangular, 5-foot deep x 8-foot wide x 10-foot long, concrete structure <br />will be installed at the downstream end of this segment. <br />3. A 995-foot long tailwater section will convey water from the stilling basin <br />to the outfall into the existing drainage downstream of the TDA collection <br />pond. This section will be constructed at an average bed slope of <br />approximately 6%, with a finished bottom width of 5 feet, side slopes of <br />2:1 (h:v) and a depth of 4 feet. The peak velocity in this segment will be <br />approximately 10 fps during the design storm event and rip rap armoring <br />will be used to prevent erosion along this segment. <br />Battle Mountain Resources, Inc. 17 <br />P:\Pmjxts1212-Ne nt(SenLWs)\SenL%i,\Pmvit An=dm t- Wei Pit Nf=gen AV5 Repon& PDFATextTetmitAmendmem_v5c.dm December 2007