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of the Section 16 Pit. Generally, Colowyo is proposing raising the post-mining topography <br />approximately 100 feet above the currently approved topography. This proposed change <br />raises several questions. First, there is an extremely steep portion of fill from <br />approximately station 110+00 to approximately station 130+00. The elevation decreases <br />400 feet over the 2,000 foot horizontal distance, which is a slope of 20%. This area <br />represents the tie-in point to the currently approved post-mining topography in the West <br />Pit based on the proposed change in the Section 16 Pit topography. There is no post- <br />mining drainage channel proposed in this location and uncontrolled sheet flow over that <br />steep of a slope will cause erosion problems. Second, the area that is located from <br />approximately cross-section 140+00 to approximately 160+00 is up to 50 feet higher in <br />elevation than the pre-mining topography. Third, Colowyo is proposing to move the small <br />"peak" that was originally located in the final cut of the Section 16 Pit approximately 2,000 <br />feet north. This is basically the area discussed in the second point. This makes the <br />proposed portion of the backfill to the south, from approximately stations 160+00 to <br />approximately station 175+00 up to 50 lower than the pre-mining topography. Please <br />review the steep portion of the Section 16 Pit backfill from approximately station 110+00 <br />to approximately 130+00, where the Section 16 Pit will tie-in to the West Pit. Colowyo will <br />need to revise this portion of the backfill to reduce this slope. Colowyo will also need to <br />propose measures to eliminate the sheet flow over this portion of the backfill. Please <br />explain why Colowyo is proposing to raise the post-mining topography in the area from <br />approximately cross-section 140+00 to approximately 160+00, where the post-mining <br />topography will be up to 50 feet higher than the pre-mining topography. Based on the first <br />and second items above, it would appear that Colowyo could better balance the cut and <br />fill in these areas to make the tie-in portion with the West Pit less steep and eliminate the <br />portion of the backfill that is up to 50 feet higher than the pre-mining topography. Please <br />explain Colowyo's reasoning for moving the "peak" in the final cut of the Section 16 Pit <br />approximately 2,000 feet north of its original location. <br />Response: The steep portion of the Section 16 Pit area along the E-E' cross section from <br />approximately 140+00 to approximately 160+00 has a design of approximately a 5.4:1 <br />slope. This is similar to slopes found elsewhere on the postmining topography. See <br />response to Comment 43c. <br />b Colowyo has proposed changes to the final cut area of the Section 16 Pit. This area <br />is currently approved as a major drainage, with the East Taylor Ditch flowing from the final <br />cut into the East Taylor Pond. With the proposed changes to the post-mining topography, <br />Colowyo has eliminated all of the drainage(s) from this final cut area. Please review the <br />post-mining topography for the final cut of the Section 16 Pit area with respect to surface <br />water runoff. Colowyo should consider altering the post-mining topography slightly to <br />incorporate several stable post-mining drainage channels. Failure to add drainage <br />channels will result in long runs of uncontrolled sheet flow over the regraded surface and <br />erosion problems. <br />Response: The final cut of the Section 16 Pit will be filled in by the new Postmining topography. <br />With the new PMT there is no longer a valley running through the center of section 16. <br />This new PMT will divert water to the revised Taylor Trib. Drainage, revised East <br />Taylor Drainage and to the Streeter Gulch Drainage. See Maps 41 and 41A for ditch <br />locations.