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<br /> <br />42. No post-mine channels have been proposed for the top of the reclaimed <br />tailings other than those resulting from final deposition as shown on <br />Figure F-3. Flow paths will approximate the pre-mining condition as <br />noted. A significant reduction in channel slope will occur between pre- <br />and post-mine conditions. Although the reduction in slope will tend to <br />reduce the potential for erosion, it will not alleviate the potential as <br />stated on page E-6. The broad flow zones (channels) created on the <br />tailings surface and shallow slopes will result in low velocities during <br />flood conditions. However, during smaller runoff events, channelized <br />flow from upstream areas may tend to cut a channel thru the Topsoil which <br />has been respread on the tailings. It may be advisable to direct this <br />flow in a constructed low-flow trickle channel rather than allow the <br />topsoil to be eroded away in finding its preferred path. Please address <br />the stability of these channels and any channel bottom treatment required <br />for low-flow conditions. <br />43. The spillway design calculations are provided in Appendix L. A velocity <br />of 10.5 fps results in the channel below the concrete control section for <br />the PMF flow event. A smaller channel for the 100-year, 24-trour event is <br />also proposed and shown on Figure F-3. The 100-year channel is proposed <br />to be riprapped while the PMF channel is proposed to be revegetated. No <br />stability calculations or construction specifications were provided. <br />Please provide the following: <br />A cross-section of the final spillway channel, <br />Riprap size based an stability calculations, <br />Riprap and bedding specifications, <br />Velocity in the revegetated section of channel, <br />Revegetation specifications if different from general <br />specifications. <br />44. The collection pond is proposed to be filled with riprap to act as <br />an energy dissipation structure for the engineered spillway upon <br />reclamation. What size riprap and thickness of riprap will be used? <br />What depth of overburden, if any, will be placed over the folded-in <br />liner? What size and thickness of riprap bedding material is proposed? <br />45. Has consideration been given to grouted riprap versus the concrete <br />proposed for the spillway entrance and control section? This may alter <br />the hydraulics somewhat but may improve the post-mine appearance upon <br />reel amati on . <br />46. Please provide a description of the reclamation to be performed at <br />Waste Rock Disposal Area D. The upper surface of each waste rock <br />disposal area should be graded to encourage drainage in a controlled <br />manner. <br />-6- <br />