2022-09-29_PERMIT FILE - C1980007 (2)

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West Elk Mlne Predicting the exact location of the faults encountered underground based on surface expressions of these faults is very difficult in this area. The BEM and 14HG Faults are good examples of this difficulty. No directly observable surface evidence was found for these two fault zones. The weak fine-grained rocks in the Mesaverde Formation have accommodated much of the fault strain as the fault propagated upward through the section. The rotational movement from vertical slip to horizontal bedding plane movement has been observed frequently at in-mine fault locations. This diminished fault offset and fault damage along with the surface colluvium and alluvium mask the surface expression of these faults. Fault and fracture zones have been mapped at the Rollins Sandstone crop along Minnesota Creek. Displacements of 1.5 feet have been observed and have been projected into and incorporated with the in-mine mapping. E Seam workings in the SOD permit revision area are expected to encounter at least two of the known and possibly two of the inferred fault systems. Previous experience with groundwater inflows associated with the BEM and 14HG Faults has provided the West Elk Mine staff with sufficient experience, established protocols and the necessary infrastructure to adequately handle another fault inflow should it occur. From the perspective of historical groundwater movement, the interception, conveyance and discharge (to the North Fork) or storage of the fault water (in the sumps) associated with mining impacts seems unlikely to have significant hydrologic consequences, in terms of groundwater quantity, because MCC knows of no claim of reliance or water rights associated with these fault inflows. Prior to construction of West Elk Mine, estimates of mine inflow were prepared using preliminary pumping test results and various analytical models. These estimates of mine inflows have been used to project the magnitude of mine water discharges and to assess the potential impact to natural patterns of groundwater rechazge and dischazge. However, standard analytical approaches for estimating groundwater inflows to the mine have been difficult to apply for the following reasons: 1. There are no aquifers in the Upper Coal Member or Barren Member of the Mesaverde Formation at the mine. There certainly are faults, fractures and formations containing groundwater within them, but these are not aquifers. As previously noted, an aquifer is defined as "a body of rock that is sufficiently permeable to conduct groundwater and to yield economically significant quantities of water to wells and springs" (Bates and Jackson 1987). Groundwater may be found in the colluvium or occasionally in sandstone units which are not continuous or correlative over distances of more than 2,000 feet. Horizontal permeabilities in the Mesaverde Formation aze quite low (approximately 1x10-5 cm/sec) and vary widely over the mining block even within individual sandstone units (see Section 2.04.7). Vertical permeabilities within the formation are expected to be two to five orders of magnitude less. Because of these extremely low vertical permeabilities, downwazd water flow within the Barren Member or Upper Coal Member appeazs to be restricted of fractures and faults which, when observed in outcrops, aze widely spaced. 2.05-255 Revised Jurce 2005 PRIO; Rev. March 2006; Rev. May 2006 PRIO