2013-07-19_REVISION - M1977311 - Laserfiche WebLink

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Response to DRMS P General Stormwater Comments of June 10, 2013 Cotter SR -13A Mine Cotter Corporation (N.S.L.) ( "Cotter ") submits this response to the June 10, 2013 letter from Tim Cazier, Division of Reclamation, Mining and Safety ( "DRMS "), to Glen Williams, Cotter. The DRMS' comments are in italics and Cotter's responses are in bold. SR -13A Mine, File No. M- 1977 -311, Amendment (AM3) Application Adequacy Review S. Page ESWMP -6, second paragraph and FlowMaster output pages. The May 24, 2013 response to this comment is adequate. However, the results of the FlowMaster analysis provided indicate the expected flow velocity exceeds five feet per second. As such, this channel will require armoring, such as riprap. The DRMS's analysis suggests any channel segment operating under the 5.16 cfs design flow and the 3H.-I V "Y" ditch will require armoring on slopes exceeding 7.6 percent. Please provide: a. An analysis to select appropriate sized riprap and Attachment 1 provides a worksheet analyzing the Offsite Basin 10 channel (Section F- F in the steep sections) for velocity using maximum slope (12 %) and minimum n (0.035) and give a maximum velocity of 5.92 feet per second (fps). Riprap was sized using the Federal Highway Administration HEC -11 methodology (Chapter 4: Design Guidelines for Rock Riprap). This analysis and copies of the relevant portions of the FHA guidelines are included in Attachment 2. The analysis indicates a minimum D50 rock size of 4.00 inches. The minimum D50 now indicated by the armoring detail shows 6" rock is required for installation. This is greater than the minimum and therefore adequate. b. Add a detail to the drawings showing the appropriate armoring and which segments will require armoring (e.g., channel segments greater than 7.6 percent). While the last set of responses and drawing revisions attempted to address the issue of armoring the steep sections (greater than 7 %) of the Offsite Basin 10 channel, we have further revised the drawings and edited the notes and details to make the requirement more visible. Sheet 2 of 6 in enclosed Attachment 3 illustrates (by magenta shading) the area along the roadway where steep slopes will exist and which will therefore be required to have armoring. The note refers viewers to the detail at the bottom of the page (Section F -F) which provides channel and rock dimensions for the steep area. 7. Page ESWMP-7, last paragraph. The DRMS appreciates the decision to breach the embankment upon the cessation of mining. In order to further reduce the potential for erosion and sediment problems, please commit to the following: a. Provide a maximum slope... The May 24, 2013 response to this comment is adequate. No response necessary; however, the revised drawing indicating the changes is now Sheet 4 of 6 in Attachment 3.