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M..y Colowyo Coal Company <br />?V 5731 State Highway 13 <br />O' Meeker, CO 81641 <br />1071 <br /> <br />rah <br />G <br />June 1, 2010 <br /> <br />Mr. James R. Stark oo ?onq? <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 />RE: Colowyo Mine's response to the Division's Preliminary Adequacy Report for <br />Technical Revision - 81. <br />Dear Mr. Stark, <br />Colowyo received the Division's incompleteness comments for TR-81 and has the following <br />comments and responses: <br />Rule 2.05.3(6) - Overburden <br />1. Section 2.05.3(6)(c) lists the requirements for the geotechnical investigation of a <br />proposed disposal site. Bedrock characteristics; adverse geological conditions; locations of <br />springs and seeps; and rock drain material characteristics have been successfully <br />addressed in previous Shannon and Wilson studies for the South Taylor area. With respect <br />to (iii), potential effects of subsidence, Shannon and Wilson issued an opinion in Addendum <br />No. 2 (November 2008) that highwall mining will not significantly affect spoil foundation <br />conditions and should not reduce the global stability of the spoil fill. With TR-81, the <br />dimensions (lateral and vertical) of the temporary and excess spoil fills have been enlarged. <br />The issue of potential subsidence has not been addressed in the October 2009 Shannon <br />and Wilson study. Please address the potential effects of subsidence of the <br />subsurface strata due to highwall mining activities, considering the proposed <br />redesigned configurations of permanent and temporary excess spoil fills. <br />Response: Please refer to Review Figure 1 (provided with this submittal for agency <br />review only and not for inclusion in the permit). It can be observed that with one exception, <br />the previously highwall mined areas are located near the edges and not under the main <br />body of the fills. The exception is the highwall mined area in the SE14 of Section 17, but at <br />this location there is only a relatively shallow temporary fill over the highwall mined zone <br />and no permanent fill (please refer to Section ST D-D' in Map 208.). Finally, the proposed <br />future highwall mining area in the SW14 of Section 17, as shown on Section ST A-A' in <br />Figure 208, will now have no overlying spoil fill under the proposed TR-81 PMT as <br />compared to as much as 200 feet in the previously approved PR-02 PMT.