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STATE OF COLORADO <br />DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866-3567 <br />FAX: (303) 832-8106 Interoffice Memo <br />To: Jim Stark <br />From: Kent Gorham KCC: Sandy Brown <br />Date: July 1, 2010 <br />RE: Adequacy review, TR-81, Colowyo Mine, C-81-019 <br />COLORADO <br />D I V I S 10 N O F <br />RECLAMATION <br />MINING <br />SAFETY <br />Jim, as per your email dated June 9, 2010, 1 have completed my review of the materials <br />submitted by Colowyo addressing the Divisions first adequacy letter (3/11/2010) for Technical <br />Revision No. 81 (TR-81) for the Colowyo Mine, #C-81-019. <br />My questions were #10, #11, #12, #14, and #15. <br />10. Response accepted. Colowyo has submitted modeling and design information for the <br />permanent ditches at the East and West Taylor fills using the 100-year storm event. <br />11. Response accepted. Ditches have been extended where necessary. Very small <br />areas of identified by Colowyo as "fill" are up gradient of 100-year diversion but are of <br />no consequence. <br />12. Colowyo has included terrace design information for terrace ditches to be used in the <br />post-mining topography. The Division concurs with the hydrologic estimates for ditch <br />design. However, the Division prefers the use of more traditional terrace ditches in <br />permanent topography rather than triangular ditches as currently designed and <br />proposed. Asymmetric terrace ditches lend themselves better to equipment access for <br />cleanout and are likely to perform better during the revegetation liability period when <br />the area is subject to increased erosion due to limited hydrologic cover. Please <br />consider more traditional terrace ditch design in accordance with Rule 4.14.2(2). <br />14. Response partially accepted. Colowyo has provided additional introductory text for <br />Exhibit 7, Item 20, Part C. However, it is not clear whether Colowyo is presenting <br />two designs or replacing the original design for the West Taylor pond. Both <br />pond designs use sumps or stock ponds as secondary sediment control <br />measures for the worst case situation. As reclamation progresses in the <br />watershed, will sumps be utilized or required? Please provide additional input <br />or discussion related to the hydrologic design for the West Taylor pond. (Jim, <br />Office of Office of <br />Mined Land Reclamation Denver - Grand )unction - Durango Active and Inactive Mines