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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 />STATE OF COLORADO <br />COLORADO <br />ID IV I S I O N O F <br />RECLAMATION <br />MINING <br />SAFETY <br />January 22, 2013 <br />John . <br />G vernoHickenlooper <br />Mr. Ton Tennyson <br />Tony y <br />Mike King <br />Executive Director <br />Colowyo Coal Company <br />57 31 State Highway 13 <br />g y <br />Meeker, CO 81641 <br />Loretta E. Pineda <br />Director <br />Re: Colowyo Mine, Permit No. C- 1981 -019, TR -95 Adequacy <br />Dear Mr. Tennyson: <br />Regarding your second adequacy letter response (dated December 13, 2012 and received by the Division on <br />December 17, 2012), I have the following comments and questions. The Division's decision on TR -95 is <br />pending answers to several questions (italicized in this letter). The first four headings correspond to the <br />comment numbers in previous adequacy letters. <br />COMMENT #1 <br />The Division recognizes that Colowyo is not requesting changes to the curve numbers in the SEDCAD <br />hydrologic model for areas reporting to the Prospect Pond; Colowyo is only requesting changes to curve <br />numbers for other areas of the mine site. In the adequacy response letter of December 13, 2012, Colowyo <br />states that, "The issues encountered within the Prospect Drainage have been unique to the Prospect <br />Drainage and are not applicable across the balance of the mining operation." Please elaborate on what <br />makes Prospect unique. <br />Ordinarily, a change in a hydrologic model (say between two different watersheds) would be justified by <br />physical differences on the ground, such as differences in soil types or vegetation, or by new information <br />on the relationship between the inputs and outputs of the model. This second justification could be <br />rainfall and runoff data that allows the modeler to calibrate his /her model. The Division understands that <br />Colowyo's proposal to change the model is not based on such physical factors or data. It is, rather, based <br />on the relative risks of pond failure between Prospect and other watersheds. The risk associated with <br />Prospect Pond failure is much greater than other ponds (in terms of public safety) due to the proximity of <br />Prospect Pond to State Highway 13. Please confirm if this understanding is correct or incorrect. If <br />correct, this is a point worth discussing. <br />Per Colowyo's December 13, 2012 letter, another justification for using different curve numbers is the <br />impact on the reclamation schedule for the mine site. The Division does not accept this as a valid reason <br />to update the curve numbers in the SEDCAD models. However, we do appreciate that Colowyo has <br />provided this information; it helps us understand Colowyo's underlying concerns related to this technical <br />revision. <br />COMMENT #2 <br />Colowyo is correct in the assumption about the Division's error. In our July 2, 2012 letter, we did mean <br />to state `B soils" rather than "C soils." Thank you for pointing out this error. <br />Colowyo states that in the past " SEDCAD modeling overestimated actual flows witnessed at Colowyo <br />Mine." What is this assertion based on? Does Colowyo have flow data or other information to confirm <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines <br />