2018-02-02_REVISION - C1981019 (9)

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RULE 2 PERMITS the Geology map (Map 7A) with the well location map (Map I IC). Thus, no impacts to these wells from any dewatering activities in the Collom pit are anticipated. There are no beneficial use wells (other than those owned and/or controlled by Colowyo) within a two mile radius of the northern pit limit of Collom. Therefore, there will be no impact on any non-Colowyo well caused by the mine dewatering operations, There is lack of groundwater communication in the vicinity of the Collom pit with any beneficial use well located near Wilson Creek. The KM layer (an aquiclude) precludes any impact of the dewatering on the upgradient wells in Wilson Creek. In addition, the dip of the KM bed and the Trout Creek sandstone top is to the north and any groundwater flow would be down dip away from Wilson Creek. An examination of the cross section illustrated in Exhibit 7 Item 22B, demonstrates that the cone of influence of the dewatering wells on the north side of the Collom Pit will be several miles from Wilson Creek and any of the beneficial use wells near Wilson Creek. With the cone of influence not extending much past the Collom Pit to the north, the KM layer acting as an aquiclude, and the dip of the KM bed away form Wilson Creek limits any potential impacts of dewatering to any benefical use wells on Wilson Creek. Potential effect on the Trout Creek Sandstone aquifer No impacts are anticipated to the quantity of groundwater in the Williams Fork Formation or the Trout Creek Sandstone of the Iles Formation. The Williams Fork Formation is not a significant water supply source in the Danforth Hills. It is not used as a source of water where the valley -fill aquifers and surface waters are accessible. The Trout Creek Sandstone aquifer is separated from the lowest coal seam to be mined by approximately 400 feet in the Collom pit area. Between this coal seam and the Trout Creek Sandstone is a mudstone/shale, sandstone, siltstone, and coal sequence of the Williams Fork Formation. About 200 feet above the Trout Creek Sandstone, a laterally continuous, smectite clay layer known as the KM bed exists. This layer has very low permeability and, therefore, is an effective barrier to vertical groundwater flow. No impacts from mining or mine dewatering activities are anticipated to the quantity of groundwater in the Williams Fork Formation or the Trout Creek Sandstone of the Iles Formation. Potential effect of minina on the groundwater flows stem The bedrock groundwater system intersected by the Collom Pit will be affected by mining and backfilling activities. The existing bedrock groundwater system is highly anisotropic because of the alternating layers in the bedrock that have permeabilities varying over many orders of magnitude. The coal seams generally comprise the higher permeability layers, the sandstones have a lower permeability and the siltstone and mudstone units have a very low permeability. The hydraulic conductivity values of the bedrock units are reported to average about 0.14 ft/d for the coal seams and about 0.006 ft/d for the sandstone units. The hydraulic conductivity value for the mudstone and siltstone units is expected to be less than 0.0001 ft/d (WMC, 2005). Mining will displace these layers within the mine footprint and replace them with a more uniform and isotropic backfill material. The permeability of the backfill will be higher than the bedrock units and will be more similar the permeability of an valley fill material. The hydraulic conductivity of the backfill is expected to be in the range of 1 to 200 ft/d. The geometric mean value of hydraulic conductivity for valley fill valley fill is about 33 ft/d (WMC, 2005) so this value is considered a reasonable estimate of the hydraulic conductivity of the backfill. Collom — Rule 2, Page 118 Revision Date: 2/2/18 Revision No.: TR -116