2013-10-17_PERMIT FILE - C1982056A (4)

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where the railroad passes over the mine workings. The location of the rail line is shown on Map 23B, Structures and Renewable Resources The worst -case impacts, due to subsiding the railroad track, could result in a train derailment. In the unlikely event that this should occur, the coal spilled from the cars would be cleaned -up to the extent practical. The coal would be either returned to the car or hauled back to TC's facility. In the event this occurred during an inclement period and ground conditions did not allow for the clean -up, the coal would be cleaned -up during the next favorable period. TC does not plan to construct any permanent roads to facilitate possible clean -up. The required mobile equipment (i.e. trucks and loaders) would drive over the tracks or immediately adjacent to the track -bed. The potential clean -up would be limited to periods of favorable field conditions, thereby reducing the chance that a road will have to be constructed into the clean -up site. A copy of the subsidence agreement between TC and the railroad is incorporated into Exhibit 7D -1. Any additional agreement letters from different parties will also be incorporated into this exhibit (7D -1). There are two locations where the track crosses Fish Creek which will require placement of additional fill at these crossings. It is anticipated that periodic clean -up of materials from the UP's normal track maintenance activities may be required. This work will be coordinated through the UP. During mining of the 9, 8, 7, 12, 13 and 14 -Right panels, the railroad track was subsided, without causing any derailments or other material damage. The track subsided as predicted and the agreed upon repair /maintenance plan was carried out without any significant problems. The track will be subsided during mining of Panels 17- and 18- Right, with similar effects and maintenance requirements anticipated. Fish Creek Fish Creek flows in a generally northerly direction through the NMD and northwesterly, through portions of the WMD. The overburden depth varies from 1,000 to 1,400 feet through the panels. The location of the creek is shown on Map 23B, Structures and Renewable Resources. Projected impacts to the creek are presented in Exhibit 7e -6, Twentymile Coal Company, AVF Subsidence Study, Final Report, prepared by SubTerra, Inc. As noted in this exhibit, subsidence varies from 0 to 67 inches over the panels. Based on the data presented in Exhibit 7e -6, the maximum increase in the stream gradient is l .1 percent. It is not anticipated this will cause significant changes to the creek's profile, and resultant erosion should not be a concern. TC has monitored similar changes in gradient in the EMD and NMD, without resultant erosional problems in Fish, Foidel, or Middle Creeks. The same type of subsidence features will occur along Fish Creek, i.e. trough - subsidence features, with differential lowering of the ground surface, minor surface cracks, and localized ponding or minor flooding (during high flow periods) over the panels. Natural ponding will tend to mitigate any localized changes in stream gradient, as flow velocities will be reduced as streamflows pass through the ponded areas. The extent of ponding, i.e. flooding of AVF, is presented in Exhibits 7e -6 (NMD) and 25Y (WMD). As indicated in these exhibits, approximately 7.3 acres will be flooded by the mining of Panels 17 -Right and 18- Right, and a maximum of approximately 39.9 acres would be flooded during high water by mining Panels 12- through 16 -Left. Prior to full extraction under the creek, a channel survey was completed in the NMD to establish the baseline used in the preparation of the Probable Hydrologic Consequences section of this application. Given, however, TC's experience with subsidence effects on Fish Creek and Foidel and Middle Creeks, it was not considered necessary to survey the Fish Creek channel in the WMD, as the dynamics of stream subsidence in this area are already well - established. Fish Creek Alluvial Valley Floor The Fish Creek Alluvial Valley Floor will be undermined and subsided during mining of Panels 17 -Right and 18 -Right in the NMD, and Panels 12- through 15 -Left in the WMD. Subsidence for the AVF will mirror that projected for the creek. The primary impact anticipated for the AVF is localized temporary pooling of water in the subsidence troughs over the mined panels and their associated subsidence areas. TR 13 -82 2.05 - 181.10 02/28/13