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i kern coal company boa 487 ~ weltlen, mloredo 80480 ~ 13031 7234721 Date• Ms. Patricia A. Nelson Colorado Department of Health Water Quality Control Division 4210 East 11th Avenue Denver, Colorado 80220 ~I~ II~II~II~~~~II~~ sss • " ~~. ~~~ ~-9 RE: KERR COAL COMPANY - MARK MINE (PERMIT N0. COG-850037), REQUEST FOR STORMWATER EXE[~TION Dear Ms. Nelson: Kerr Coa' Company (Kerr) owns and previously operated the Marr Mine, located approximately fourteen miles east of t:.e town of Walden, Colorado. Mining operations at the mine have ceased and the mine is curre__-_tly in an active reclamation mode. Drainage and sediment control for the mining related disturbance is provided by a number of engineered sedimentation ponds, collection/diversion ditches, and associated drainage structures. Discharge from the sedimentation ponds is controlled and regulated under applicable provisions of Permit COG-850037. Discharge for the twelve individual outfalls under this permit comes almost exclusively from snowmelt runoff, with no process water discharge and discharge from rainstorms being rare. All sedimentation ponds are designed and maintained to provide a minimum detention time of at least 24 hours for retained runoff resulting 'nom the 10 year, 24 hour storm event. While the ponds are designed to provide adequate detention time to allow settlement of suspended solids, due to the characteristics of the dominant soil tyres in this area both undisturbed and disturbed area runoff typically have relatively high levels of suspended solids. In addic'_on, a relatively high percentage of the suspended solids in the ru-:off are fine colloidal materials which do not readily settle out of suspension. During periods of high flow due to either snowmelt or rainfall runoff, the noted factors combine to limit the trapping efficiency of the existing sedimentation ponds with the result that concentrations o: certain parameters in pond discharge may exceed applicable offluent limitations. The accompany monitoring report(s) indicat=_ exceedance of effluent limitations for the following discharge point(s), effluent parameters(s), and monitoring pericd:s) for which an exemption is requested.