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COLORADO <br />Division of Reclamation, <br />Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />August 20, 2018 <br />Chris Gilbreath <br />Tri-State Generation and Transmission Association <br />12050 North Pecos St. Suite 100 <br />Westminster, CO 80234 <br />Re: New Horizon Mine (Permit No. C-1981-008) <br />Technical Revision No. 84 (TR -84) <br />Adequacy Review <br />Dear Mr. Gilbreath: <br />The Colorado Division of Reclamation, Mining and Safety (Division) received your application for TR - <br />84 for the New Horizon Mine on July 11, 2018. The application was deemed complete on July 21, 2018. <br />TR -84 is proposing address the post -mining topography, backfill and grading plan, tailwater ditch design <br />on ERMR property, and movement of Bench 1 overburden to the previously approved Slash M, LLC <br />Adjacent Support Facility. The Division finished its review of the TR -84 application has the following <br />adequacy questions or comments. <br />SedCad model for Pond 16 as built certification, 10yr 24 hour storm event Sediment Volume <br />Estimate. It appears that the pond has the capacity to contain this event. <br />a) Why are spillway dimensions particularly slopes, different in the as built model when <br />compared with the postmining model? <br />b) Why is the bottom width of the spillway different in the as built model when compared <br />with the postmining model? <br />c) Also, why is the crest length different between as built and postmining models? <br />d) The cover page reads Sediment Volume Estimate for 100 yr, 24 Hour Storm. This is <br />incorrect it should read for 10 year 24 Hour Storm. Please revise and resubmit cover <br />page. <br />2. SedCad model for Pond 16 as built certification, 100yr 24 hour storm event, Containment <br />Analysis. It appears that the pond has the capacity to contain this event. <br />a) Why are spillway dimensions particularly slopes, different in the as built model when <br />compared with the postmining model? <br />b) Why is the bottom width of the spillway different in the as built model when compared <br />with the postmining model? <br />c) Also, why is the crest length different between as built and postmining model? <br />flF'C-0 <br />H <br />1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us I <br />John W. Hickenlooper, Governor I Robert W. Randall, Executive Director I Virginia Brannon, Director * r 1876 4 <br />