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TRI-STATE GENERATION AND TRANSMISSION ASSOCIATION, INC. <br /> HEADQUARTERS: P.O. BOX 33695 DENVER, COLORADO 80233-0695 303-452-6111 <br /> August 24, 2018 <br /> Mr. Brock Bowles <br /> Environmental Protection Specialist <br /> Colorado Division of Reclamation, Mining and Safety <br /> 1313 Sherman Street, Room 215 'vEp <br /> Denver, CO 80203 R�G� <br /> RE: New Horizon Mine (Permit No. C-1981-008) AUG <br /> Technical Revision No. 84 (TR-84) <br /> Adequacy Review Response Division of&esa etyion, <br /> Nlining <br /> Dear Mr. Bowles: <br /> Tri-State Generation & Transmission Association (Tri-State) has received your adequacy <br /> review letter for TR-84, dated August 20, 2018 and provides the following responses to your <br /> comments on behalf of the Elk Ridge Mining and Reclamation's New Horizon Mine. <br /> 1. SEDCAD model for Pond 16 as-built certification, 10yr-24 hour storm event Sediment <br /> Volume 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 /> Response: The dimensions are different because the postmining model reflects the design <br /> prior to construction. Since the as-built reflects actual constructed conditions, the <br /> postmining model in Attachment 2.05.3(3)-29 is being removed from the PAP. <br /> b) Why is the bottom width of the spillway different in the as built model when compared <br /> with the postmining model? <br /> Response: See response (a) above regarding spillway dimensions. <br /> c) Also, why is the crest length different between as built and postmining models? <br /> Response: See response (a) above regarding spillway dimensions. <br /> d) Cover page reads Sediment Volume Estimate for 100 yr, 24 Hour Storm. This is incorrect <br /> it should read for 10 year, 24 Hour Storm. Please revise and resubmit cover page. <br /> Response: The SEDCAD cover pages have been revised to remove storm event reference. <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 /> Response: The dimensions are different because the postmining model reflects the design <br /> prior to construction. Since the as-built reflects actual constructed conditions, the <br /> postmining model in Attachment 2.05.3(3)-29 is being removed from the PAP. <br /> b) Why is the bottom width of the spillway different in the as built model when compared <br /> with the postmining model? <br /> Response: See response (a) above regarding spillway dimensions. <br /> c) Also, why is the crest length different between as built and postmining model? <br /> Response: See response (a) above regarding spillway dimensions. <br /> AN EQUAL OPPORTUNITY/AFFIRMATIVE ACTION EMPLOYER CRAIG STATION ESCALANTE STATION NUCLA STATION <br /> P.O.BOX 1307 P.O.BOX 577 P.O.BOX 698 <br /> A Touchstone Energy'Cooperative CRAIG,CO 81626.1307 PREWITT.NM 87045 NUCLA,CO 81424-0698 <br /> / +,0� 970-824-4411 505-876.2271 970.864-7316 <br />