2016-05-04_PERMIT FILE - C1982056 (7)

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TC contracted with SubTerra, Inc. to expand the subsidence predictions to further evaluate impacts to Fish Creek and its AVF for mining operations in the Wadge Coal Seam in the Eastern and Northern Mining Districts, and in the Wolf Creek Seam in the Wolf Creek Reserve. These reports are presented in Exhibits 7E, 7E-1, 7J, and 7K. These reports provide numerical analyses of subsidence cross-sections through the subsided areas, and also use a 3D Geologic Modeling software program (GEMCOM) to compare against the mathematical model. The results of the mathematical model show that subsidence associated with planned mining in the WCR has the potential to increase the surface area of Foidel Creek by approximately 5 acres, and Fish Creek by 70 acres, and to result in a change in gradient for Fish Creek of up to 2.4% (Foidel Creek negligible due to the small area potentially affected). For both drainages, the extent of potential flooding during high flows would be controlled by the elevation of the channel where it overlies the gateroads (high points) and bank height immediately upstream from these locations. TC conducted a vegetation study of the AVF bottomlands and adjacent upland areas to evaluate vegetation parameters for the respective areas. The study is presented in Exhibit 7J-1, Northern Mining District, Fish Creek Vegetation Study. The study data indicate higher cover but lower palatability and productivity for the upland vegetation (94.2%/48.1%/1,096 lbs/ac), when compared to the bottomland vegetation community (83.4%/66.2%/2,434 lbs/ac). It is reasonably anticipated that mining -related subsidence would lower ground levels relative to the typical stream gradient, resulting in localized increases in bottomland vegetation in subsidence areas, with the potential for minor increases in the overall productivity of the associated range and pasturelands. The entire length of Fish Creek overlying the Eastern and Northern Mining Districts (corresponds to WCR area) was surveyed to look for outcrop areas. The survey showed that approximately 1,260 feet of channel in Section 10, TSN, R86W has an exposed rock outcrop (Fish Creek Sandstone). In this area, surficial cracking could occur, with the potential for surface or ground water drainage. In this area, however, the cover is greater over the longwall panels, with an increased thickness of low permeability shales. The combination of greater cover depths and thicker shale deposits minimizes the potential for surficial cracking and drainage during and after mining. Based both on these considerations and TC's previous experience in undermining this area in the overlying Wadge Seam, TC does not anticipate any significant surface or ground water drainage or loss of flow in either Fish Creek or Foidel Creek as a result of the planned mining operations in the WCR. In the unlikely event that surface or ground water drainage were to occur, Table 72B, NMD Recharge Time Estimate, provides the number of days it would take to fill in the additional fracture volume resulting from subsiding the bedrock. This is a very conservative estimate due to the character of the stream. The data presented assumes that sandstone bedrock can be found for the entire length of Fish Creek overlying the panels, and this is not the case. The section in which the sandstone unit is exposed is the approximate 1,260 feet of channel in Section 10, TSN, R86W. The remainder of the channel is alluvial material overlying the Lewis Shale, which given its composition and character, would swell to fill any cracks that might occur. Fish Creek meanders over portions of the WCR mining area. Using the relationship of stream length to recharge volume, the volume of water lost from the stream system under worst —case conditions would be negligible when compared to total stream flow volumes. Presently, there are no active irrigation ditches established along the potentially affected portion of Fish Creek or Foidel Creek, which irrigate a designated alluvial floor within the limits of the planned WCR mining area. This is due to the fact that it is not economically feasible to establish an irrigation system on the limited acres formed by these meandering creeks. As is the case for all the lands along Fish Creek and Foidel Creek to be undermined and subsided, no flood irrigation system has been established to increase the productivity of the land, nor are the management practices established for haying this area. An alternate to active irrigation is the utility of sub - irrigation to enhance crop production. The potential for sub -irrigation to occur depends upon depth of rooting of selected species and water table elevation during the growing season. Data collected previously by P & M indicate there are restricted areas in which sub -irrigation does occur. The extent of sub -irrigation, based on vegetation type, was verified during the 1997 growing season by vegetation production studies within the defined Fish Creek AVF. These areas are not cropped and are managed as unimproved rangeland. In considering the potential water quality impacts of mining and subsidence, ongoing monitoring at Station 900 on Foidel Creek, which is downstream of the previous mining in the Eastern Mining District and near the eastern limit PR14-10 2.06-25.8 08/10/15