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^ l~~,~~rrn e ~ I g9CP A ~ 3003 , <br />i '~ppendis~ ~ <br /> <br /> <br />I~ <br />1 <br /> <br />kerr coal company <br />ne^ ae~ v..~aen, ~m,.m aoaao iii naa~si <br />Date: ~J ~ <br />III IIIIIIIIIIIIIIII ~~~`~`~ <br />Ms. Patricia A. Nelson <br />Colorado Department of Health <br />Water Quality Control Division <br />4210 fiast 11th Ave..^_ue <br />Denver, Colorado 80220 <br />r% 13/97 <br />. ~ ~~ <br />,~ <br />RE: RERR COAL COMPANY - PD1RR MINfi (PERMIT N0. <br />COG-850037), REQUEST FOR STORMwATER fixfiMP'PION <br />' Dear Ms. Nelson: <br />Kerr Coal Company (Kerr) owns and previously operated the <br />Marr Mine, located approximately fourteen miles east of the tows 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 disturbance is provided by <br />a number of 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 Pezmit COG-850037. Discharge for the twelve <br />individual oucfalls under this permit comes almost exclusively frcm <br />' snowmelt runoff, with no process water discharge and discharge from <br />rainstorms being rare. <br />AlI sedimentation ponds are designed and maintained to <br />1 provide a minimum detention time of at Ieast 24 hours for retained <br />runoff resulting from the 10 year, 24 hour storm event. While the <br />ponds are designed to provide adewate 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 />t solids. Zn 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 in pond discharge may exceed <br />applicable effluent limitations. The accompany monitoring <br />report(s) indica~a exceedance of effluent limitations for the <br />following discharge point(s), effluent parameters(sl, and <br />monitoring oeriad(s) for which an exemption is requested. <br />