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,~ <br />kerr coo! company <br />hox 487 ~ Walden, caloredo 80480 - (3031 723721 <br />Date: <br />Ms. Patricia A. Nelson <br />Colorado Department of Health <br />Water Quality Control Division <br />4210 East 11th Avenue <br />Denver, Colorado 80220 <br />Ill IIIIIIIIIIIIIIII <br />~, <br />:~~~ <br />RE: KERR COAL COMPANY - MARR MINE (PERMIT N0. <br />COG-850037), REQUEST FOR STORMWATER EXII4PTION <br />Dear Ms. Nelson: <br />Kerr Coal Company (Kerr) owns and previously operated the <br />Marr Mine, located approximately fourteen miles east of t::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 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 Pe_mit COG-850037. Discharge for the twelve <br />individual outfalls under this permit comes almost exclusively frcm <br />snowmelt runoff, with 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 for 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 in pond discharge may exceed <br />applicable effluent limitations. The accompany monitoring <br />report(s) indicate exceedance of effluent limitations for the <br />following discharge point(s), effluent parameters(s), and <br />monitoring period;s> for which an exemption is requested. <br />