2015-11-16_PERMIT FILE - C1981019 (6)

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RULE 4 PERFORMANCE STANDARDS deeper coal seams. Based on this information, the CDMG determined that the South Taylor pit does not meet the criteria for mountaintop removal. 4.27 OPERATIONS ON STEEP SLOPES Prior to the approval of Technical Revision 81 (TR -81), over 18% of the South Taylor pit area was greater than 20 degree slopes, and over 30% of the pit area was greater than 15 degree slopes (Figure 2.06.4 -1). Those areas were identified around most of the perimeter, and scattered isolated locations within the pit. Therefore, an application for a variance from approximate original contour for steep slope mining was appropriate for the South Taylor pit. Colowyo requested this variance in the cover letter to Permit Revision 2 (PR -02). This variance is no longer needed, as a result of the changes to the mine plan in TR -81. Norwest Corporation originally prepared the Post Mine Topography (PMT) for the South Taylor mining area in 2006 based on the Operations on Steep Slopes section of the regulations. The design was based on the mine plan prepared by Marston Mining Engineers & Consultants and the following methodologies were followed: 1. Ridgelines from the original topography would be used to maintain each drainage area. 2. Drainage channels from the original topography would tie into the undisturbed area surrounding the mine. 3. Waste materials would not be placed back into the pit under Approximate Original Contour (AOC); alternatively, the pit would be backfilled and the external waste dumps would be re- contoured. 4. The final PMT was designed with SurvCADD Natural Regrade software to create a more stable land form and drainage system. The configuration of the mining plan will not allow the pit to be backfilled until the end of the mine life. An initial PMT design was based upon conventional methods to generate a PMT surface to maintain the drainage basins using ridgelines from the original topographic map. The final PMT was developed using SurvCADD Natural Regrade. The area was subdivided into eight areas, different drainages, and sub - drainages. The geofluvial design of the channels and drainage basins was established to control the surface water to minimize the effects of erosion and assist in reestablishing vegetation. Cut and fill volumes were modified to reduce the material by lowering the fills and raising the cuts. The final material movement for the South Taylor mining area according to this plan was approximately 114.3 million cubic yards of cut and 115.4 million cubic yards of fill. It included two valley fills near the headwaters of Taylor Creek, one referred to as the East Taylor Fill and the other West Taylor Fill, and a large temporary spoil stockpile needed to develop the mine pit. With the more recent mine plan that no longer extends as far into the NW /4 of Section 21 or the SE /4 of Section 20, a revised mine plan has been adopted. This results in an overall smaller pit footprint and reduced overburden and backfill volumes than those originally approved in the South Taylor mine plan in PR -02. To enable development of the box cut, the out -of -pit valley fills included in that PR -02 are still necessary, and it is necessary to extend the toe of the East Taylor Fill by approximately 900 feet and the West Taylor Fill by approximately 600 feet, in order to accommodate the temporary spoil piles needed to establish the box cut. That extension is one of the major items in technical revision TR -81. The above described pull -back of the southeasterly limit of the pit results in the mine plan and PMT as described in Mine Plan Map 23A and Map 45 of TR -81. As is evident on the cross section drawings associated with those maps, the TR -81 PMT more closely resembles pre- mining topography than that previously approved in PR -02. The temporary spoil stockpiles are depicted on Map 45. The need for a permanent valley fill in the headwaters of West Taylor Creek in the SW /4 of Section 17 and the NE /4 of South Taylor /Lower Wilson — Rule 4, Page 22 Revision Date: 10/31/13 Revision No.: MR -129