2018-05-18_PERMIT FILE - C2009087A (3)

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RULE 2 - PERMITS the mine after 26 months mining, within about 2,100 feet after 60 months, and within bout 5,000 feet of the mine after 420 months of mining (30 years after the end of the permit period). Figures 2.05.644, 2.05.6 -F4.1, and 2.05.6 -F4.2 present maps showing the horizontal extent of drawdown 26, 60 and 420 months after of the start of mine dewatering. Note that for clarity on Figures 2.05.6 -F4 and 2.05.6 -1 certain drawdown contours were omitted because they were very close to the contours for the expected hydraulic conductivity scenario. The omitted contours include the following: • Figure 2.05.6 -174: drawdown contours for 1000, 500, 100 and 5 feet for the low hydraulic conductivity scenario and 1000, 500 and 100 feet for the high hydraulic conductivity scenario, • Figure 2.05.6 -F4.1: drawdown contours for 1000, 500, 100 and 5 feet for the low hydraulic conductivity scenario and 500 feet for the high hydraulic conductivity scenario. Map 2.04.7 -M2, Surface Diversions, Reservoirs, and Water Supply Wells, presents overlying points of diversion and water storage facilities relative to the PSCM permit boundary and surface disturbance. All of the permitted wells are outside of the 5 -foot drawdown contour, which indicates that the mine dewatering operations will not adversely affect the availability of groundwater to present users. In addition, the potential for drawdown to affect the gaining reach of Grassy Creek (see Robson and Stewart, 1990, Table 3, Grassy Creek Stations shown on p. 38), where the creek crosses the outcrops of the Trout Creek Sandstone and Williams Fork Formation at the southwestern perim of the PSCM permit area, and springs in that area is minimal. As explained in more detail in the paragraph below, the Twentymile and Trout Creek aquifers are hydrologically isolated from the Wadge coal and so will not be affected by mining - related drawdown. The subcrop of the Wadge coal beneath the gaining reach of Grassy Creek is outside of the 5 -foot drawdown contour and so will not be affected by mine - related drawdown. Consequently, none of those units (the Twentymile and Trout Creek aquifers and the Wadge coal) could cause mining- related effects to the gaining reach of Grassy Creek. The springs in the vicinity of the southwestern perim of the PSCM permit area are all outside of the 5 -foot drawdown contour and so will not be affected by mine - related drawdown. The vertical extent of potentiometric head changes in the bedrock units will be limited by the low permeability and thickness of shale beds above and below the Wadge coal. Previous studies, as well as monitoring at the nearby Foidel Creek Mine, indicate that the major regional sandstone aquifers (the Twentymile and Trout Creek aquifers), which occur, respectively, approximately 600 feet above and 235 feet below the Wadge coal, are hydrologically isolated from the Wadge coal and the small section of the overburden unit to be disturbed by mining at the PSCM. They are therefore unlikely to be affected by the proposed mining. The isolation is created by the very small hydraulic conductivities of the intervening shale sequences above and below the Wadge coal and its overburden and underburden. The interval separating the Wadge coal from the overlying Twentymile aquifer includes approximately 540 feet of marine shale. Shale samples from this area tested for vertical permeability, as reported by Williams and Clark (1994), gave values less than 10 -6 ft/d. The interval separating the Wadge coal from underlying Trout Creek aquifer includes shale • beds but more notably includes a hydrologically - significant, regionally- extensive bed of altered volcanic ash (kaolinitic claystone, or "tonstein ") referred to as the Yampa Bed by Brownfield and Johnson (2008). Where tested in other areas (Water Management Consultants (WMC), 2005), PSCM Permit App. 2.05 -75 Revision 03/05/10