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June 25, 2012 <br />Dear Mr. Zuber, <br />5731 Highway 13 <br />Meeker, Colorado 81641 <br />970 - 824 -1500 <br />Mr. Rob Zuber <br />Environmental Protection Specialist <br />Colorado Division of Reclamation, Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />ocom° <br />JV1N 2 ?01? <br />; rcedamation, <br />M i n i n g and Safety <br />Tony Tennyson, Environmental Engineer 970- 824 -1532 <br />RE: Technical Revision No. 95, Hydrologic Methods Revision, Permit No. C- 1981 -019. <br />Colowyo received your letter dated June 1, 2012 and has the following responses to your <br />comments: <br />• Over the last five years, the Division, Colowyo Coal Company staff, and CCC consultants <br />have put in a great deal of time and effort focused on preventing water quality violations <br />and improving the safety of public users of Highway 13 below Prospect Pond. This effort <br />has included improving modeling accuracy. Colowyo most recently updated the <br />approved curve numbers at the mine through technical revision 73 (TR -73, June 2009). <br />As part of TR -73, Colowyo identified soils on the mine site as C soils and associated CN <br />values were approved. <br />Response: Colowyo Coal Company is aware of the sensitivity regarding Prospect pond and its <br />proximity to Highway 13. In view of this, CCC is proposing with this response to <br />retain the TR -73 input assumptions for the Prospect basin, specifically the curve <br />numbers assigned in TR -73. A revised Table 1 is attached which retains the TR- <br />73 Curve Numbers for Prospect but seeks to revert toward the historically used <br />Curve Numbers for all other areas. This change would bring the Colowyo <br />modeling more into line with the neighboring mines in Moffat and Routt <br />Counties as well as the recommended practices presented in Part 630 `Hydrology" <br />of USDA NRCS National Engineering Handbook (NEH). <br />