2010-07-16_REVISION - C1981019 - Laserfiche WebLink

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discrepancy in the reclamation dates for the face of the West Taylor and East Taylor Fills. Please explain why Colowyo has proposed to change the dates of reclamation for the face of the West Taylor and East Taylor Fills. Please include a discussion of the reclamation of the fills in Section 4.09, including the timing of the reclamation and the reasoning for the timing. 43. With the submittal of the responses to the Division's preliminary adequacy review letter for Technical Revision 81, Colowyo has proposed changes to the post-mining topography for the South Taylor area. Colowyo, for the most part, appears to be returning the South Taylor area to its approximate original contour. The Division has reviewed revised post- mining topography Maps 19 and 19A and has the following questions and comments. a. Colowyo has provided a new cross-section for the revised post-mining topography for the final cut of the Section 16 Pit. This cross-section is E-E' and is shown on Maps 19 and 20A. This cross-section shows the proposed post- mining topography for the final cut of the Section 16 Pit. Generally, Colowyo is proposing raising the post-mining topography approximately 100 feet above the currently approved topography. This proposed change raises several questions. First, there is an extremely steep portion of fill from approximately station 110+00 to approximately station 130+00. The elevation decreases 400 feet over the 2,000 foot horizontal distance, which is a slope of 20%. This area represents the tie-in point to the currently approved post-mining topography in the West Pit based on the proposed change in the Section 16 Pit topography. There is no post- mining drainage channel proposed in this location and uncontrolled sheet flow over that steep of a slope will cause erosion problems. Second, the area that is located from approximately cross-section 140+00 to approximately 160+00 is up to 50 feet higher in elevation than the pre-mining topography. Third, Colowyo is proposing to move the small "peak" that was originally located in the final cut of the Section 16 Pit approximately 2,000 feet north. This is basically the area discussed in the second point. This makes the proposed portion of the backfill to the south, from approximately stations 160+00 to approximately station 175+00 up to 50 lower than the pre-mining topography. Please review the steep portion of the Section 16 Pit backfill from approximately station 110+00 to approximately 130+00, where the Section 16 Pit will tie-in to the West Pit. Colowyo will need to revise this portion of the backfill to reduce this slope. Colowyo will also need to propose measures to eliminate the sheet flow over this portion of the backfill. Please explain why Colowyo is proposing to raise the post-mining topography in the area from approximately cross-section 140+00 to approximately 160+00, where the post-mining topography will be up to 50 feet higher than the pre-mining topography. Based on the first and second items above, it would appear that Colowyo could better balance the cut and fill in these areas to make the tie-in portion with the West Pit less steep and eliminate the portion of the backfill that is up to 50 feet higher than the pre-mining topography. Please explain Colowyo's reasoning for moving the "peak" in the final cut of the Section 16 Pit approximately 2,000 feet north of its original location.