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Response to DRMS Adequacy Review(2)—Cotter-9 Mine Reclamation Plan Amendment <br /> S. Please address the reclamation/post mining plan for the retention pond. The August 1, <br /> 2013 response is partially adequate. Sheet S of 10 shows a nearly five foot drop at <br /> 3H.-1 Vat the toe of the embankment with no defined channel. This steep section will <br /> erode with successive runoff events and lead to sediment problems. The DRMS suggests <br /> cutting the outfall to the original grade or designing a defined armored channel. Please <br /> revise the design. <br /> The revised pond drawings now indicate an elongated chute for the pond discharge which <br /> eliminates the steep drop originally shown at the bottom edge. The reclaimed chute is <br /> now indicated to be a consistent slope all the way to the end. This is indicated on the <br /> revised drawings included in Attachment 4 of this document. <br /> 6. Page ESWMP-25, 72" CMP analysis; DDP Drawing 3 of 7; and Figure C2. <br /> a. ...photo #8 is the 72" CMP. The August 1, 2013 clarification response is <br /> adequate. <br /> b. Please review the last two rows of Attachment A. The August 1, 2013 <br /> clarification response is adequate. <br /> Additional sections have been analyzed in accordance with the "Attachment A" <br /> provided by DRMS review. These sections can be seen in the attachments in these <br /> responses along with flow analysis calculations. <br /> c. Provide outlet protection design for the culvert... The August 1, 2013 response <br /> indicates the subject culvert will be removed. The DRMS is concerned about <br /> potential scour and sediment problems related to the removal of the culvert and <br /> embankment. Please provide the DRMS with the following: <br /> i. A drawing profile through the embankment showing the existing grade <br /> and embankment and the proposed grade after removal. <br /> ii. A cross section showing cut slopes similar to those shown in Drawings on <br /> Sheets 6 through 8. <br /> iii. Analyses demonstrating the resulting cut slopes will be stable during the <br /> 100 year, 24-hour design peakflow. <br /> A channel profile, cross-sections, and flow analyses are provided for the new <br /> configuration proposed for the large culvert removal. These are shown in the <br /> Attachments 1, 2, and 4. <br /> d. The embankment through which this culvert conveys stormwater...Please see <br /> Comment 6.c.i-iii above. <br /> The analysis provided in 6.c applies to the channel and the embankment. <br /> 4 <br />