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STATE OF COLORADO <br />DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866 -3567 <br />FAX: (303) 832 -8106 <br />June 1, 2012 <br />Kurtis Blunt <br />Colowyo Coal Company <br />5 731 State Highway 13 <br />Meeker, CO 81641 <br />Re: Colowyo Coal Company, Permit No. C -81 -019, TR -95 — revision of hydrologic methods, <br />Preliminary adequacy <br />Dear Mr. Blunt: <br />COLORADO <br />Q I V I S I O N O F <br />RECLAMATION <br />MINING <br />SAFETY <br />John W. Hickenlooper <br />Governor <br />Mike King <br />Executive Director <br />Loretta E. Pineda <br />Director <br />Your technical revision application (TR -95) was considered complete for the purposes of filing on May <br />4, 2012. The Division has reviewed your revision application and has a request for additional <br />information. <br />We need additional information to justify the change in curve numbers. The Division requests that the <br />following points be addressed. <br />• Over the last five years, the Division, Colo «yo Coal Company staff, and CCC consultants <br />have put in a great deal of time and effort focused on preventing water quality violations and <br />improving the safety of public users of Highway 13 below Prospect Pond. This effort has <br />included improving modeling accuracy. Colowyo most recently updated the approved curve <br />numbers at the mine through technical revision 73 (TR -73, June 2009). As part of TR -73, <br />Colowyo identified soils on the mine site as C soils and associated CN values were approved. <br />• CCC references the 1981 report by Striffler and Rhodes, "Hydrologic and Erosional <br />Characteristics of Regraded Surface Coal Mined Land in Colorado," which includes sample <br />sites at eleven surface mines in Colorado. Specific to Colowyo, the sampling was done on 11 <br />acres of lands reclaimed at Colowyo in 1978. Colowyo now has thousands of acres of <br />reclaimed lands. On page 14 of this report, the authors state, "However, any generalizations <br />about the similarities of surface hydrology or regraded coal mined land from state to state, <br />between areas within a mining region, or even between sites within a mine are risky due to <br />critical site specificity." Thus it is not clear that past studies at Colowyo, let alone studies at <br />other mine sites, provide justification for altering CN values. <br />• Additional information would provide better rationale for altering the CN values. This could <br />include site specific infiltration tests and /or calibration of existing models using rainfall and <br />runoff data. <br />Regarding other changes to Exhibit 7, please explain the rationale behind all substantive changes. In <br />particular, please explain the reasoning for updating the sediment loading parameters in Table 6. <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines <br />