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Colowyo Coal Company <br />5731 State Highway 13 <br />Meeker, CO 81641 <br />0 <br />Owe <br />0 December 7, 2009 <br />Mr. James R. Stark Div" ,on, <br />Environmental Protection Specialist Mining and Safety <br />Colorado Division of Reclamation, Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />RE: Colowyo Mine's response to the Division's Incompleteness Letter for <br />Technical Revision - 81. <br />Dear Mr. Stark, <br />Colowyo received the Division's incompleteness comments for TR-81 and has the following <br />comments and responses. <br />Rules 2.05.3(6) - Overburden and Rule 4.14 - Backfilling and Grading <br />1. On Page ST/LW-Rule 4, Page 20 Colowyo has changed the swell factor for <br />the South Taylor spoil from 20% (in the original PR-02 submittal) to 15%. Colowyo <br />will need to provide documentation and discussion for this decrease in swell factor. <br />Based on the decrease in swell factor, it follows that there will be less overburden <br />from the mining operations available for backfill and, therefore, less spoil that would <br />be required in a permanent fill(s). Please explain why Colowyo has decreased <br />the swell factor for the South Taylor spoil yet increased the total amount of <br />permanent, excess spoil from approximately 60 million cubic yards to <br />approximately 70 million yards. <br />Response: In the mine plan for South Taylor permitted under PR-02, a swell factor <br />of 20 percent was used for all material volumes. This was a conservative <br />assumption because of the significant quantities moved by dragline. A swell factor <br />of 15 percent is used for the plan provided under TR-81 because the materials in the <br />permanent spoil piles are moved by truck/shovel. <br />More importantly, the pit limits have changed and the toes of the permanent fills <br />have moved northward. This has changed the PMT tie in boundary. Permanent fill <br />volumes are calculated between the proposed postmine surface and the premining <br />surface at the PMT tie-in boundary and the pit limit. Intuitively, increasing the area <br />within this boundary results in a larger volume in permanent fill spoil piles.