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~~~ <br />COTTER <br />November 5, 2004 <br />Received <br />aov o s toot /~ <br />Grand Junction Field p{npg <br />D(vision of Murerals & tieob0y <br />~e~`d <br />Steve Shuey f <br />Colorado Division of Minerals and Geology <br />Grand Junction Field Office <br />~y ~-~ it-s-a~/ <br />555 <br />101 S. Third St, Room 301 <br />Grand Junction, Colorado 81501 <br />RE: Permit No. M-1978-116 SM-18(Wright) Mine, Responses to Questions of Third <br />Adequacy Review, AM-1 <br />Mr. Shuey: <br />The enclosed responses are numbered to correspond to the ADEQUACY ISSUES <br />requested by you in your letter to Cotter Corporation dated November 5, 2004. There are <br />two copies of all items. <br />4. a) Appendix D (included with Cotter's response dated November 1, 2004) <br />showed the calculations for the median stone size, Dso, needed to protect the <br />two berm segments where the flow from the two subbasin will enter the <br />diversion ditches. The document referred to in Appendix D, NUREG/CR- <br />4651,May 1987, DeveloQment of Ripran Design Criteria by Riprap Testing in <br />Flumes: Phase I, recommends that the riprap thickness be a minimum of 1.5 <br />times the Dso~ <br />b) The riprap will be placed over the entire width of the diversion channels <br />in the bean segments referred to in Appendix D. <br />c) The diversion channels will be excavated deep enough to allow a <br />finished depth of up to 2 feet after the rock is placed. The calculated flow <br />depths fora 10-yr event at Berm Segment 1 is 0.243 ft and at Berm Segment 2 <br />it is 0.345 ft. The calculated flow depths fora 100-yr event at the segments <br />are 0.452 ft and 0.648 ft, respectively. It is obvious that the target depth of 2 <br />feet for the diversion channels is oversized by a factor of 3, or more. <br />As mentioned in Appendix D, the berms will be protected during the life <br />of the mining operation. The final footprint of the reclaimed waste rock dump <br />will depend on the size of the pile attained during mining. The larger rock <br />calculated for the 100-year event at berm segment 2 will not be placed until <br />final reclamation is complete. At that time, particularly if the waste rock pile <br />Cotter Corporation -West Slope Operations Telephone (970) 864-7347 <br />P.O. Box 700, 28151 DD Road, Nucla, CO 81424 USA Fax (970) 864-7287 <br />