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Response to DRMS Adequacy Review (2) —Cotter SM -18 Mine Reclamation Plan Amendment <br />-i - <br />6 Page ESWMP -7, section 7.5 and Page ESWMP -23. It is not clear whether the pond <br />volume is for the existing pond (Sheet I of S) or proposed improvement (Sheet S of S). <br />Please provide clarification. <br />The pond volume referenced on page ESWMP -23 of the original report was <br />for the proposed pond 20 with grading improvements. A new <br />elevation/volume table is included in Attachment 6 along with sheet 5 in <br />Attachment 7 indicating the revised grading and required limits of the <br />proposed elevation contours. <br />7. Please address the reclamation, post mining plan for the retention ponds. The DRMS <br />strongly encourages breaching the embankment upon closure unless the landowner has a <br />use for the ponds (e.g., stock pond) and intends to maintain them. <br />As suggested at final reclamation, it is now the intent to breach, or fill, the <br />ponds to an elevation allowing storm water to pass through the site without <br />retention. This is indicated on the revised drawings (sheets 9, 10, and 11) <br />included lulled as Attachment 7. <br />8. Sheets I and S of 5. No spillways or low level outlets are provided for the retention <br />ponds. Please provide spillway locations, designs (sections and profiles), and <br />specifications sufficient to convey the design flow to the toe of the embankment. <br />New spillway design and low -level outlet drain details are included in <br />Attachment 7 (sheets 6, 7, and 8). Broad - crested weir calculations are <br />included In Attachment 6, <br />9. Sheets 3 and 4 of S. Each section lists a water surface elevation and velocity. In reference <br />to Comment 44 above, please be sure the water surface elevation corresponds to the <br />Manning's n used for capacity and the velocity corresponds to the Manning's n used for <br />stability. <br />The channel cross - sections have been revised to reflect water surface <br />elevations and velocities and labeled with the corresponding n values used to <br />determine the conservative value of each. These new sections. are included in <br />Attachment 7 (sheets 3 and 4). <br />7 <br />