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TRI -STATE GENERATION AND TRANSMISSION ASSOCIATION, INC. HEADQUARTERS: P.O. BOX 33695 DENVER, COLORADO 80233 -0695 303 - 452 -6111 May 5, 2014 Mr. Robert Zuber, P.E. Environmental Protection Specialist Colorado Division of Reclamation, Mining and Safety 1313 Sherman Street, Room 215 Denver, CO 80203 RE: New Horizon Mine (C- 1981 -008) RECEIVED TR-63 Third Adequacy Review Response Trench Drain Design MAY 0 '2014 Division of Reclamation Dear Mr. Zuber: Mining & Safety Western Fuels - Colorado (WFC) has received your third adequacy letter for TR -63, dated May 1, 2014 and provides the following responses to your comments. I . No further response required. 2. No further response required. 3. No further response required. 4. No further response required. 5. More information is required regarding the selection of rock sizes in the design. Your response addresses the ability of the pipe to handle the load of rock and spoil, but this is not a complete explanation of how rock size is determined. There is no published design methodology available to follow in the selection of rock sizes for the Rock and Trench Drain structures. Therefore, the rock sizes were determined based on professional engineering judgment in constructing similar structures. By mimicking French Drain construction methodology, washed pit run rock one to four inches will be placed approximately two feet around the perforated pipe on both the Rock and Trench Drain structures. The size rock was selected as it is large enough not to clog up the pipe and will not create void space that can create settling issues. It will also allow enough pore space between individual rocks which will not impede water flow into the system. On the Trench Drains, above the smaller rock, a larger sized rock (5 " -10') will be placed prior to backfill. This rock size was selected as it is not large to create significant void space within the Trench Drain and it also creates a competent underground surface to aid in mitigation of deferential settling within the backfill material above the drainage system. This rock size is also porous enough to facilitate water movement into the Trench Drain as designed. The details listed above are also shown on the revised Map 2.05.3(3) -21 included herein. 6. No further response required. 7. No further response required. 8. No further response required. 9. No further response required. 10. No further response required. AN EQUAL OPPORTUNITY/ AFFIRMATIVE ACTION EMPLOYER A Touchstone Energy' Cooperative CRAIG STATION ESCALANTE STATION NUCLA STATION Y.O. BOX 1307 P.O. BOX 577 P.O. BOX 698 CRAIG, CO 81626 -1307 PREWITT, NM 87045 NUCLA, CO 81424 -0698 970- 824 -4411 505 -972 -5200 970 - 864 -7316