2017-03-23_PERMIT FILE - C1981019A

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RULE 2 PERMITS The valley fill groundwater system in the West Fork of Jubb Creek is not anticipated to be affected by mining. The Jubb Creek area disturbed by mining is small, less than 3% of the total watershed area, and most of the recharge to the valley fill groundwater system will come from spring runoff from the higher elevation portions of the watershed. No measureable impacts to stream base flow are anticipated. Dewatering water entering the valley fill groundwater system will not add asignificant amount to the total system compared with the total amount of groundwater currently in the system. Potential effect on existing Groundwater users in the area The Collom mine area and the surrounding land is predominantly owned and/or controlled by Colowyo Coal Company and/or its subsidiaries. There are numerous monitoring wells on these lands which are registered by Colowyo as wells under Colorado State Engineer's rules and regulations. Thus, any well within the limits of the Collom permit expansion is owned and controlled by Colowyo and the only impact from any dewatering will be on Colowyo itself. Table 2.04.7-44 and Map 11 C reflect the location, ownership and control status of these wells. The closest known and registered/permitted non-Colowyo owned domestic or commercial wells are located approximately two miles southeast of the initial Collom boxcut area. These wells are located in the SWI/4, Section 7, T.3N., R.93W and are completed below the base of the Williams Fork formation, in the Iles Formation, or in valley fill material along Wilson Creek. This can be verified by comparing the Geology map (Map 7A) with the well location map (Map 11 C) as well as the plan view and cross section illustrated in Figures 2.05.6-1 and 2.05.6-2, respectively. 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, The lack of groundwater communication in the vicinity of the Collom pit with any beneficial use well located in Wilson Creek is illustrated on Figures 2.05.6-1 and 2.05.6-2 in Volume 15. Three typical dewatering wells from the WMC (2005) report are projected onto the cross section in Figure 2.05.6-2 to aid in understanding the effects of the dewatering cones of influence surrounding the dewatering wells. This is a conceptual plan to aid in the understanding of the location of the Collom pit and the closest non- Colowyo beneficial use wells in Wilson Creek. The southern limit of the cross section is near the location of several beneficial use wells located in Wilson Creek. (This can be seen by reviewing Map 11C with Figure 2.05.6-1). An examination of the cross section illustrates that the cone of influence of the dewatering wells on the north side of the proposed pit will be several miles from Wilson Creek and any beneficial use wells near Wilson Creek. In addition, the KM layer (an aquiclude) precludes any impact of the dewatering on the upgradient wells in Wilson Creek. Finally, 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. 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. Collom —Rule 2, Page 118 Revision Date: 11/16/16 Revision No.: MR -166