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May Day/Idaho Mine - Chief Drainage Channel Reclamation Work Plan Comments <br />Page 3 <br />May 27, 2011 <br />10. It appears from Figure 1 that the invert of the proposed channel is approximately 10 feet <br />higher than the low spot on the Chief Adit bench. This is not acceptable. The <br />reclamation drainage channel invert should match the pre-disturbance invert elevation. <br />This will prevent a failure of the berm on the north side of the channel from allowing <br />runoff to report to the adit and/or the scour of bench material; and reduce the potential for <br />the outfall of the reclaimed channel from head cutting upstream. <br />11. Figure 1 does not show the existing natural upstream channel invert or centerline. Please <br />add this to the drawing so the Division can evaluate the alignment between existing and <br />proposed channel bottoms. The drawing should also indicate the extent of disturbance. <br />12. The section presented in Figure 2 indicates there is an adverse gradient from Station 0+00 <br />to about 0+20 where ponding will occur. The reclaimed channel should not be allowed to <br />pond unless it can be demonstrated that this was the natural condition prior to the <br />disturbance. <br />13. The section from Station -0+80 to 1+07.07 shows a slope of approximately 1.611:1V (or <br />60 percent). This suggests this is material placed at angle of repose and likely mine <br />waste. Again, the proposed invert should match the pre-disturbed channel invert or the <br />applicant needs to demonstrate to DRMS that this was the pre-disturbance channel slope. <br />DRMS will require protecting this steep section (if it was naturally this steep) unless it <br />can be demonstrated to be non-erodible material, such as bedrock. If the channel was this <br />steep and non-erodible, an energy dissipation structure is required at the bottom, which is <br />not shown on Figure 2. Please extend the section line to meet the natural undisturbed <br />channel invert. <br />14. Standard drafting convention for section lines is that the prime () A - A' appears on the <br />right end of the line in order to make it clear from which direction the viewer is observing <br />the section. <br />Appendix A, Chief Drainage Channel Reclamation Best Management Practices: <br />15. The second, third, and fourth BMP sheets suggest pipes or culverts are proposed as part <br />of the reclamation channel design. Please indicate where pipes or culverts are to used on <br />Figures 1 and 2. <br />16. The mulch BMP sheet (page 111) mentions hay. Hay is not allowed as stated in <br />Comment #5. Also note that mulch is most suitable for flat or gently sloping areas, as <br />stated in the second paragraph of the mulch BMP. This site has very little flat or gently <br />sloping areas. <br />17. There is a vegetative filter BMP included (p. 121). Note these are grassy areas and it <br />may not be feasible to establish a good stand of grass to perform as a filter. Where is the <br />vegetative filter to be implemented? If it is not to be used, please remove it from <br />Appendix A. <br />18. The silt fence barrier BMP sheet states silt fences can be used in minor swales or ditches <br />(p. 126). DRMS does not allow silt fences to be used in channels of any kind, <br />perpendicular to the flow direction. <br />If either you or the applicants have any questions regarding the comments above, please call me <br />at (303) 866-3567, extension 8169. <br />cAdocuments and settings\whe.naturenet\local settings\temporary internet <br />files\content.outlook\580z7cpc\ldg_wrkplnlcomments mem27mayll.docx <br />? . , _?, a ..??..? -}.....?._ ._ ...?,.? . ..?.. ,, ,