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:~ Richartl D. Lamm Governor • DEPARTMENT OF NATURAL RESOURCES Davitl H. Getches, Executive Director MINED LAND RECLAMATION DI\ DAVID C. SHELTO N, Director December 6, 1983 Mr. Donald H. Simpson Colorado Department of Health Water Quality Control Division 4210 East 11th Avenue Denver, Colorado 80220 RE: NPDES Permit CO-0027154 Dear Mr. Simpson: Colorado Yampa Coal Company has requested that the Mined Land Reclamation Division provide a letter of verification on sediment pond designs. This is required by their recently issued IVPDES permit CO-0027154. MLRD has reviewed the pond designs for all discharge points. We have found that the ponds have been designed, constructed, and maintained to contain or treat the volume of water from active mining areas which would result from a 10-year, 24-hour storm event. The 10-year, 24-hour event, for design purposes, was estimated at 1.8 inches and is taken from the U.S. National Oceanic and Atmospheric Administration Atlas 2. Precipitation at the mine is monitored at the Main Mine weather station. The following table provides the runoff volume resulting from a 10-year, 24-hour precipitation event for each discharge point. Discharge Point I.D. Location 10-y r, 24 hr RunoFf Volume As-Built Runoff Storage Volume 001 Eckman Park, Pond A 52.3 ac-ft 73.6 ac-ft 002 Mine 1, Pond T 3.4 ac-ft 3.4 ac-ft 003 Mine 1 Pond B 0.86 ac-ft 3.9 ac-ft 004 Mine , 1 Pond C 1.1 ac-ft 1.1 ac-ft 005 Mine , 1 Pond D 13.9 ac-ft 51.0 ac-ft 006 idine , 1 Pond E 1.9 ac-ft 1.9 ac-ft 007 Mine , 1 Pond F 0.60 ac-ft 1.21 ac-ft 008 Nine , 1, Pond G 20.3 ac-ft 20.3 ac-ft 014 Mine 3, Pond E 1.52 ac-ft 1.52 ac-ft 423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. (303) 866-3567 ~ III IIIIIIIIIIIII III