2018-09-04_PERMIT FILE - C1980007A (40)

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West Elk Mine • There is a very small risk (WWE has calculated the risk to be less than one percent) that one or more of the stock ponds in the permit area could be adversely affected via surface cracks. Pond water could be diverted into locally permeable zones within the overburden where it could: (1) Migrate down -dip toward the North Fork or Dry Fork to become part of the tributary alluvial/colluvial contribution of baseflow to the stream system, (2) Reappear as an ephemeral seep or spring, or (3) Become trapped as storage in an isolated zone within the overburden. If any of these circumstances were to occur, they would render the affected stock pond temporarily' useless for retaining surface water. However, the lost water would eventually return to the Dry Fork and/or North Fork. The stock pond embankments could conceivably be affected by surface cracking; although, the probability of this occurring is insignificant. It is important to note that the overburden materials in the permit area contain numerous shale and claystones layers and lenses which tend to undergo plastic deformation under compression, thereby sealing fractures that develop. In addition, the sediment load within surface flows (especially during spring runoff) will tend to fill surface cracks which may develop, thus further reducing the potential to transmit water downward. The most severe potential subsurface hydrologic consequences include: • Formation of interconnected fractures in the fracture zone with local water -bearing units of the overburden, thereby inducing either: (1) The movement of groundwater from one formation to another or (2) Loss of water to the mine workings. Should diversion to the mine occur, this water will be collected, treated, and discharged into the North Fork or the Dry Fork (see discussion above regarding the implications of surface water discharges to the North Fork and Dry Fork). As discussed extensively within this permit document, there are no regional aquifers within the Mesaverde Fon-nation in the vicinity of West Elk Mine, nor is there demonstrated formation groundwater use at the mine or in the general area. Consequently, there are no aquifers which could be damaged as a result of subsidence.. While there has been a sizeable amount of groundwater inflow observed from recently encountered fault systems (BEM and 14HG) there is no evidence to indicate any use of that water regionally. In addition, the observed inflows from these fault systems have decreased over time to a small percentage of the initial inflows, similar to other groundwater encounters in the mine. • Interconnection of fractures filled with water and methane (as reported in the Oliver No. 2 Mine) with the mine workings via the B or E Seam fracture zone. This subject is discussed lager in this section and in Exhibit 60. As discussed in Section 2.05.6(6)(e)(i) Potential Impacts ftoin Local Seismic Activity, subsidence could accelerate the naturally -occurring rock -fall and landslide propensities that are already evident in the pennnit area, but this will not constitute a hazard to either people or property nor would this meas- urabl, innpact the surface or ground water hydrology of the area. Cracking of the earth along or across the trails or unimproved roads of the coal lease area already naturallv occurs. but in the "worse case" could be accelerated by, or additional cracks created by, subsidence. As the trails and roads are unimproved, typically only all -terrain or four-wheel drive vehicles are utilized and rough terrain is expected, so the hazards created by any additional 2.O5-118 Revised June 200.1 PRIG, Rev. March 2006; Alla; 2006 PRIQ. Nov. 2006TR107,Apri12007TR108;Sep. 2007 PR12; Feb. 2008 PR -12