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COLOWYO COAL COMPANY L.P. 5731 State Highway 13 Meeker, Colorado 81641 (970)824-1572 (970) 824-1598 FAX ~II ~I~II~~I~I~~~ II~ ~ .Energy, RECEIVED ~(~,yu CnalConrPaayb,P ~) James A. Kilter Senior Environmental Engineer July 14, 1998 Ms. Carla J. Lenkey Water Quality Control Division, CDPHE 4300 Cherry Creek Dr. S. Denver, Colorado 80246-1530 JUL 16 1998 Division of Minerals & Geology Re: Request For Alternate Limits Due to Snowmelt, Additional Information CDPS Permit No. COG-850017, Moffat County Dear Ms. Lenkey: VIA FEDEX This letter is in response to your letter dated June 8, 1998 where the Water Quality Control Division (WQCD) has indicated that the burden of proof requirements for the greater than 10- yearl24-hour event was not established for outtall 007A (also known as the Prospect Pond) during March 1998. As such, the WQCD indicated that the noted discharge parameter settleable solids was out of compliance. The purpose of this letter is to provide additional burden of proof information relevant to the subject discharge. We are confident that after review of this additional information the WQCD will make a finding that an event greater than the 10-year/24-hour event occurred at ouffall 007A and all discharges are in compliance. The additional burden of proof information we are submitting today discusses 1) the very significant volume of water discharged from the pond during the period March 23 - 26, 1998 which exceeded a number of consecutive 10-year/24-hour design events for pond 007A, 2) the occurance of a similar significant Snowmelt event at a neighboring surface coal mine, the Trapper Mine, with similar results and 3) the occurance of the estimated 500-year snowmelt/flood event occurring in the town of Craig during the same week. 1~ The volume o~ond discharge exceeded the 10-yearl24-hour event. The sediment control pond 007A is designed to provide the capacity to at least contain the runoff or equivalent Snowmelt from a 10-year/24hour storm event. Colowyo worked very closely with the Colorado Division of Minerals and Geology (CDMG) utilizing SEDCAD II software to determine the correct sizing for the pond. According to page 4 of the SEDCAD model (attached as Exhibit 1 - "Prospect Pond -- Hydrology, Sedimentology and Water Control Structures") the total estimated water runoff volume entering the pond for the 10-year/24-hour precipitation event is 0.56 aGft. The pond was built oversized to insure that Colowyo would have sufficient capacity to handle such an inflow amount. According to page 12 of the approved SEDCAD model, the total water capacity of the pond up to the top of the riser pipe (referred erroneously in the model as "permanent pool") is 7.08 aclft. In summary, the capacity of the pond is 1264% greater than the containment volume required to comply with the regulations.