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Colowyo Coal Company <br />PO+• 5731 State Highway 13 <br />0 Meeker, CO 81641 <br />T: 970-824-1500 <br />Z <br />1-1h. <br />0 24 June 2009 <br />Mr. James R. Stark <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 />GS`\1 r,-1 D <br />J \et\ o` ? d S eti?a, <br />vN 25???? <br />MAro9 <br />RE: Colowyo Mine's response to the Division's Preliminary Adequacy Review <br />for Technical Revision - 78. <br />Dear Mr. Stark, <br />Colowyo received the Division's preliminary adequacy comments for TR-78 and has <br />the following comments and responses. <br />The Division does not agree with the use of hydrologic soil cover complex (CN) <br />values of 56 for 3 year and older reclamation within the Prospect watershed. In <br />the Division's opinion and in the absence of significant, site-specific supporting <br />evidence or documentation, a curve number this low does not accurately <br />represent the hydrologic soil cover conditions for these more mature reclaimed <br />areas. The Division waiting for responses from Colowyo on a pending <br />technical revision (Technical Revision 73), that proposes to change the curve <br />number values from specific values to a range of values. Please use a CN of <br />75 or higher, or respond to pending TR-73 to allow for proposed curve number <br />ranges. Revise the Prospect Pond 10 year, 24-hour model as appropriate. <br />The Division would prefer to promptly resolve the curve number issue pending <br />in TR-73. <br />Response: The requested changes have been made. Recently, the mine <br />responded to TR-73 regarding the appropriate curve numbers to use for <br />various hydrologic conditions. These new curve numbers have been <br />applied to the SEDCAD model and these results are included with this <br />submittal. These materials, which were originally formatted as Appendix <br />Exh. 7, Item 14P are now submitted as Appendix Exh. 7, Item 14R. This <br />was necessary to accommodate submittals for the small area exemption <br />and the South Taylor Haul Road Ditch. <br />2. To comply with Rule 4.05.9(2)( c)(ii), please submit SEDCAD modeling that <br />demonstrates that the Prospect Pond spillway system will safely pass the 25 <br />year, 24-hour storm event. Unless ditches A, B, and C are designed to divert