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<br />45. At the time of detoxification and decommissioning of the heap, it appears <br />that only the solution volume contained in circulation from the final <br />stage of 700,000 tons is available for use in rinsing the heap. As the <br />entire 6,500,000 tons on the pad will need to be rinsed, please address <br />the volume of water required, where will this come from and what amount <br />of time will be necessary to rinse the entire heap. It is also important <br />to document whether the ponds will provide sufficient storage capacity <br />during this operation? Please include these volumes in the water balance <br />calculation in Appendix G. <br />47. Please document how the evaporation volume required near shutdown can be <br />accomplished in the two month time period as shown on the model output in <br />Appendix G. <br />Section D.9 Diversions and Sediment Control and Drainage Crossings <br />Section D.9.1 Diversions <br />48. In Appendix H, it is difficult to correlate the watersheds sh~~wn on <br />Figure H-1 with the watershed name used to identify each model run. <br />Please provide a summary table which correlates the ditch segment name, <br />model run watershed name, watershed shown on Figure H-1 and peak flow. <br />49. All of the hydraulic lengths appear to be longer than expected. What <br />estimation method was used to derive these parameter values? If these <br />were underestimated, please provide revised peak flows as appropriate. <br />50. The capacity of the ditches are acceptable at the shallow sloi>es used in <br />the calculations, and indeed may be oversized. However, no e~+aluation of <br />channel-bottom stability was performed as a part of ditch des~gn. At <br />100-year, 24-hour peak flows, the velocities are erosive (e. g. Type 2 <br />channel at 228 cfs equals 10 fps at 1.7 foot flow depthl. The stability <br />of the ditches should be evaluated and channel-bottom treatments <br />specified for the slope conditions to be encountered along thE~ ditch. <br />Riprap sizing or other treatment criteria should be shown. For temporary <br />channels a 10-year, 24-hour peak flow would be appropriate, for permanent <br />channels a 100-year, 24-hour design storm should be used for estimating <br />peak flow. <br />51. A segment of upland diversion ditch is shown to traverse the west pit <br />face. This does not appear to be a preferred design due to stability <br />concerns. If this segment can be redesigned, please do so. If it <br />cannot, describe what measures will be taken to ensure long-term <br />stability. Please clarify whether this ditch will be a permanent <br />structure. <br />52. No design storm runoff calculations were provided for the ditches below <br />the waste rock disposal facilities What method was chosen for sizing <br />ditches, and how was the adequacy of this design evaluated? <br />53. Please provide peak flow calculations for the South Waste Rock Disposal <br />Facility haul road culvert. <br />-8- <br />