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. _ kerr coal company box 487 ~ Walden, Colorado 80480 ~ (3031 723-4721 Date. Ms. Anne lltlenfeldt Colorado Depanment of Health Water Quality Control Division 4210 East 11th Avenue Denver, Colorado 80220 cc: Farnlall P REf.Fl~%~n MAY 10 1993 Price III III~IIIIIIIIIIII sss Division of i~~~~~~~w,~ ~ --~- ~~S' Re: Rerr Coal Company - Mazr Mine (Permit No. COG850021), Request for Stormwater Exemption Dear Ms. Ihlenfeldt: Rerr Coal Company (Kerr) operates the Mazr Mine, located approximately fourteen miles east of the town of Walden, Colorado. Drainage and sediment wntrol for the mining related disturbance is provided by a number of engineered sedimentation ponds, wlleaion/diversion ditches, and assodated drainage structures. Discharge from the sedimentation ponds is controlled and regulated under applicable provisions of Permit COG850021. Discharge for the twelve individual outfalls under this permit comes eadusively from either predpitation or snowmelt runoff, with no process water discharge. All sedimentation ponds are designed and maintained to provide a minimum detention time of at least 24 hours for retained runoff resulting from the 10 year, 24 hour storm event. While the ponds aze designed to provide adequate detention time to allow settlement of suspended solids, due to the characteris[ia of the dominant soil types in this area both undisturbed and disturbed area runoff typically have relatively high levels of suspended solids. In addition, a relatively high percentage of the suspended solids in stormwater runoff aze fine colloidal materials which do not readily settle out of suspension. During periods of high flow due to either snowmelt or preapitation runoff, the noted factors combine to limit the crapping efficienry of the existing sedimentation ponds with the result that Total Suspended Solids (fSS) and Settleable Solids concentrations in pond discharge may eased applica le ffluent limitations. The accompanying monitoring report(s) for pond(s)303 %,~¢TSS) ~ ifuJ indicate eaceedance of TSS and/or Settleable Solids limitations for the mrrespon ng monttoring period. Eaceedance of appliable permit effluent limitations resulted from: ^ Discharge from rainfall runoff oaurring within 48 hours after measurable preapitation has stopped Discharge from snowmelt runoff occurring within 48 hours after runoff inflows to the pond(s) have stopped Documentation of preapitation and snowmelt occurrence and snowmelt inflows to the ponds is retained at the minesite and is available for inspection by authorized agenry representatives.