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Response to DRMS Adequacy Review (4) — Cotter LP -21 Mine Reclamation Plan Amendment <br />The berm callout now references a section (B -B) instead of a "detail ". <br />16 Sheet S, Retention Pond 50: Grading and Details: <br />a. Please provide material and compaction specifications to limit rock size, <br />preclude inappropriate debris, and ensure sufficient compaction for the <br />embankment. <br />Construction specifications have been added to sheet 3 for the pond <br />embankment. <br />b. Do the contours in the Rock -Lined Channel represent top of riprap or <br />top of subgrade? <br />The channel contours for section D -D represent subgrade and are so <br />labeled on the plan sheet 5 of Attachment 8. <br />c. The downstream end of the Rock -Lined Channel is at a 3HJV (33.3% <br />slope) below elevation 6417. The analyses show only the 5% grade. Please <br />demonstrate the riprap is stable at 3H:1 V. <br />The downstream end of the rock-lined channel where the 3:1 slope is <br />proposed has been indicated to contain larger riprap (D5o =12 ") to provide <br />additional erosion protection at the splash pad. An analysis of the riprap <br />sizing was performed using the Federal Highway Administration method <br />included in Attachment 7. <br />d Please provide spillway location, designs (sections and profile), and specifications <br />sufficient to convey the design flow to the toe of the embankment. <br />Riprap specifications are included on the revised sheets 5 & 6 of Attachment <br />8. <br />General Comments: <br />17. Page ESWMP -5, third paragraph. The NRCS is referenced as the "National <br />Resource Conservation Service". The "N" stands for "Natural", not "National". <br />We acknowledge the error regarding "N" in NRCS and will correct that <br />reference in future correspondence. <br />18. The DBMS understands the portal is currently closed Should the portal be re- <br />opened, stormwater controls will need to be designed and implemented to control <br />runoff from the portal area and roads utilized to transport ore to the ore pad from <br />the portal such that potentially impacted runoff is directed to a retention pond. <br />Cotter acknowledges the fact that the stormwater controls would have to be <br />modified to include the portal area in question should it be reopened. <br />8 <br />