2010-07-16_REVISION - C1981019 - Laserfiche WebLink

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b. Colowyo has proposed changes to the final cut area of the Section 16 Pit. This area is currently approved as a major drainage, with the East Taylor Ditch flowing from the final cut into the East Taylor Pond. With the proposed changes to the post-mining topography, Colowyo has eliminated all of the drainage(s) from this final cut area. Please review the post-mining topography for the final cut of the Section 16 Pit area with respect to surface water runoff. Colowyo should consider altering the post-mining topography slightly to incorporate several stable post-mining drainage channels. Failure to add drainage channels will result in long runs of uncontrolled sheet flow over the regraded surface and erosion problems. c. While Colowyo is proposing to regrade the majority of the South Taylor area to approximate original contour, there is still a large area on the east side of the pit that will remain below AOC. Based on a review of cross-section ST-C-ST-C', from approximately station 38+00 to approximately station 70+00, this area will be up to 100 feet lower than the pre-mining topography. Please explain why Colowyo is proposing to lower the post-mining topography in the east portion of the South Taylor Pit by up to 100 feet. d. On cross-section ST-A-ST-A', from approximately station 0+00 to approximately station 10+00 there is a small "bump" of backfill shown that is approximately 20 feet high. There is no disturbance shown on this area on Map 19B that would account for this "bump". Please review cross-section ST-A-ST-A', from approximately station 0+00 to approximately station 10+00 on Map 20B. If this "bump" is, in fact, a true feature, please add it to Map 19B and explain what it is. If this "bump" is a remnant from previous versions of the post- mining topography please revise as necessary. 44. With the submittal of the responses for Technical Revision 81, Colowyo has provided updated pages South Taylor/Lower Wilson - Rule 4, Pages 30-32. These pages encompass discussions on Rule 4.27, operations on steep slopes. Based on discussions with the operator and based on the proposed post-mining topography maps, cross- sections and mine plan map (Maps 19, 19A, 20, 20A, 20B and 23A) provided with the responses, it does not appear as though Colowyo will be operating on steep slopes. The steep slope mining was the area in the east of the currently approved South Taylor Pit, which is now proposed for elimination with this revision. A review of Map 19A - Post- Mining Topography-South Taylor Area and the associated cross-sections, it appears as though Colowyo is returning the pit to approximate original contour and no longer requires a variance from AOC for steep slope mining. Based on a review of the enclosed materials and revised pages South Taylor/Lower Wilson - Rule 4, Page 30-32, the Division has the following questions. a. On revised page South Taylor/Lower Wilson - Rule 4, Page 30 (beginning at Rule 4.27) there is a discussion of the steep slope mining conditions in the South Taylor Pit. Since Colowyo has proposed to eliminate the steep slope areas from the South Taylor Pit, this discussion is no longer valid. The Division recommends "leaving this information in the permit text for historical purposes but all of the language needs to be changed to discuss what was originally permitted