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kerr coal Company °•4 ~ ~.~ <br />' box 487 ~ .r~iCan, colontlo 80480 ~ f30.t~ 713<711 ~~ <br />' Dace: 9 <br />1 Ms. Patricia A. Nelson <br />Colorado Department of Health <br />' Water Quality Control Division <br />4210 East 11th Avenue <br />Denver, Colorado 80220 <br />' RE: RERR COAL COMPANY - I~IRR MINE (PERMIT N0. <br />COG-850037), REQUEST FOR STORI~TATER EXII4PTION <br />Dear Ms. Nelson: <br />Rerr Coal Company (Rerr) owns and previously operated the <br />1 Marr Mine, located approximately fourteen miles east of c::e town of <br />Walden, Colorado. Mining operations at the mine have ceased and <br />the mine is currently in an active reclamation mode. Drainage and <br />sediment control for the mining related diaturbaace is provided by <br />a number pf engineered sedimentation ponds, collection/diversion <br />ditches, and associated drainage structures. Discharge from the <br />' sedimentation ponds is controlled and regulated under applicable <br />provisions of Permit COG-850037. Discharge for the twelve <br />individual outfalls under this pensti.t comes almost exclusively from <br />snowmelt runoff, wieh no process water discharge and discharge from <br />rainstorms being rare. <br />All sedimentation ponds are designed and maintained to <br />' provide a minimum detention time of at least 24 hours far retained <br />runoff resulting from the 10 year, 24 hour storm event. While the <br />ponds are designed to provide adequate detention time to allow <br />' settlement of suspended solids, due to the characteristics of the <br />dominant soil types in this area both undisturbed and disturbed <br />area runoff typically have relatively high levels of suspended <br />' solids. In addition,.a relatively high percentage of the suspended <br />solids in the runoff are fine colloidal materials which do not <br />readily settle out of suspension. <br />During periods of high flow due to either snowmelt or <br />rainfall runoff, the noted factors combine to limit the trapping <br />efficiency of the existing sedimentation ponds with the result that <br />concentrations of certain parameters is pond discharge may exceed <br />applicable effluent limitations. The accompany monitoring <br />report(s) indicate exceedance of effluent limitations for the <br />following discharge paint(s), effluent parameters(s), and <br />monitoring perio~(s) for which an 2xemption is requested. <br />