2015-10-06_PERMIT FILE - C1981019A (3)

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RULE 4 PERFORMANCE STANDARDS steady state of operation where the advancing overburden face moves southward at the same rate as the advancing backfilling benches. The temporary out of pit stockpile is expected to remain in place until the final two years of mining activities. At that time, this material will be needed to fill the final pit void. Colowyo is currently targeting many coal seams at this time and an eventual box cut depth of approximately 600 feet in the Collom Lite Pit as illustrated on Map 24C. Colowyo currently operates under a variance for contemporaneous reclamation under pit configurations less than half as deep as the Collom Lite pit, mining fewer individual coal seams in the process. Because of the multi -seam nature of the mining operation described in Section 2.05, backfilling and grading cannot be completed within 180 days following coal removal. Backfilling and grading will be completed in variance of the 180 day requirement in a manner previously approved and described below, and in Sections 2.05 and 4.14.1. As shown on the mining Typical Pit Cross Section (Map 24C), mining will be carried out in any one area for a considerable length of time (approximately five years to reach the lowest coal seam). A series of benches will be necessary in the operation to recover the lower coal seams, and an additional series of benches will be necessary to dump the shovel/truck overburden material in a configuration that achieves the topography shown on the post -mining Topography Map (Map 19C). When multi -seams are mined, backfilling and rough grading cannot begin until the lower-most seam is mined. See Spoil Grading Map (Map 29B), which shows the time frames in which grading will occur in relation to the time of removal of "X" seam coal, which is shown on the Mine Plan Map (Map 23B). As mining progresses to the south, overburden material from each successive cut will be backfilled into the previously mined out area and the additional spoil will continue to buildup in previously mined areas. Initially a temporary out of pit spoil pile will be created to the North of the Collom Lite Pit and will remain in place until the end of mine life. Table 2.05.6-5 presents a mine wide volumetric calculation in support of post mining topography and illustrates that permanent out of pit spoil will not be needed. The backfilled mining areas will be graded to establish a stable post mine topography that blends into the undisturbed areas outside the mining limits (Map 19C). Colowyo will grade all final slopes so that overall grades do not exceed 3H: IV (Map 20C). As described on Map 29B, backfilling and grading activities are scheduled to be completed in the Little Collom X pit area not impacted by the development of the temporary overburden stockpile, approximately five years after initial mining begins. Map 23B describes the anticipated mining progression in the Little Collom X pit. Immediate backfilling of the Little Collom X pit is precluded by the potential for highwall mining resource opportunities in this location (not currently shown or sought at this point in time) in addition to the initial center boxcut location serving as a significant interception point for runoff and snowmelt collection during the initial boxcut development of both proposed pits. Where necessary, the regraded spoil surface will be roughened by ripping or discing etc., to ensure a bond between the topsoil and spoil to reduce slippage. To date there is no evidence of topsoil slippage on reclaimed areas in the existing permit area. A few small tension cracks resulting from settling of fill and topsoil have occurred in a few areas within a year or two after reclamation, but soon stabilize and begin to fill in. The final surface as shown on the Post -mining Topography Map (Map 19C) will approximate the overall pre -mining grades (Map 19D). Appropriate cross sections that show the anticipated final surface configuration of the proposed permit area, in conjunction with the existing pre -mining topography, are shown on the Pre -mining and Post -mining Cross Section (Map 20C). Collom — Rule 4, Nage 28 Revision Date: 9/28/11 Revision No.: PR -03