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Response to DRMS Adequacy Review (4) — Cotter LP -21 Mine Reclamation Plan Amendment <br />the ability to accomplish this. Sheet 2 of Attachment 8 provides the notes <br />and alignment. <br />14. Sheet 3, Drainage Channel Cross - Sections & Details: <br />a. Section B B. The proposed retention berm is to be constructed from <br />onsite material. Depending on available material, large rocks and/or <br />debris could be used in the construction, but should not. Please provide <br />material and compaction specifications to limit rock size, preclude <br />inappropriate debris, and ensure sufficient compaction for the berm. <br />Reasonable berm construction specifications utilizing native materials <br />and resources are provided on revised sheet 3 of Attachment 8. <br />Constructed berms and embankments on this site are not subjected to <br />continual flows. They will be operational only during fairly significant <br />precipitation events occurring on a very infrequent basis in the and <br />climate existing in the area. The operators will be inspecting them on a <br />regular basis and after known significant precipitation events. <br />Maintenance of berms and embankments will be done as required to <br />maintain the effectiveness of these structures. <br />b. Section C -C. Please show the location of the proposed diversion ditch on <br />Sheets 1 and/or 2 as appropriate. <br />Section C -C is the roadway and ditch along the western side of Onsite <br />Basin 30 and is shown on sheet 2 of Attachment 7. <br />c. Section D -D: <br />i. Please provide riprap specifications to include gradation, shape, <br />specific gravity, and durability, <br />ii. Please provide a minimum depth (from top of riprap in the invert to <br />top or riprap armor on the side slope) dimension. <br />iii. Please provide a filter layer specification for a piping barrier <br />between the native soil and the riprap. (Note: geotextile fabric is <br />not recommended for slopes greater than 10 %. A granular filter <br />should be used for slopes > 0.10). <br />Riprap specifications and installation depths and limits have been added to <br />sheet 6 of Attachment 8. A filter layer is not specified given the infrequent <br />nature of operation and the regular inspection frequency of the operator. <br />15. Sheet 4, Portal Culvert Grading & Details. The retention berm callout <br />references a "Detail" on Sheet 3. On Sheet 3 the retention berm is shown as a <br />section. The Sheet 4 callout should be a section and reference Section B B / Sheet <br />3. <br />7 <br />