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RULE 2 PERMITS <br />influence for each well to interfere with another within 500 feet and allow the water level to be dropped <br />around the pit in a reasonable timeframe. The wells well be placed within approximately 500 feet of the <br />projected pit outline and within the upslope area of the pit. This will allow total dewatering of the first <br />cuts. After the cuts are mined, then dewatering will cease, as the pit floor will be above the anticipated <br />saturated water level (— 7150 feet amsl) <br />Minor pumping of water entering the pit from draining of the perched aquifers from the south may be <br />required to remove this water to facilitate mining. <br />Thus during the dewatering, since there are no beneficial use wells (other than those owned and /or <br />controlled by Colowyo) within a two mile radius of the northern pit limit of Collom Lite, there will be no <br />impact on any non - Colowyo well. <br />The lack of ground water communication in the vicinity of the Collom Lite pit with any beneficial use <br />well located in Wilson Creek is illustrated on Figures 2.05.6 -1 and 2.05.6 -2 in Volume 15. Figure 2.05.6- <br />1 shows the plan view of the Collom Lite pit outline and its location with respect to the upper section of <br />Wilson Creek. The location of the cross section A -A' is also shown on this figure. Three dewatering <br />wells are projected onto the cross section line to aid in understanding the effects of the dewatering cones <br />of influence surrounding the dewatering wells. This is only a conceptual plan to aid in the understanding <br />of the location of the Collom Lite pit and the closest non - Colowyo beneficial use wells in Wilson Creek. <br />The second figure shows the cross section A -A'. On the cross section, the premining topography is shown <br />as well as the KM layer and top of Trout Creek sandstone and their outcropping in Wilson Creek. The <br />southern limit of the cross section is near the location of several beneficial use wells located in Wilson <br />Creek. (This can be seen by reviewing Map 11 C with Figure 2.05.6 -1). <br />Three projected dewatering wells are placed on the cross section to show the effect of the cone of <br />influence around the wells (based on past pumping test data) and how they will aid in dewatering the pit. <br />The projected dewatering wells on this figure are based on the current plan and may change as hydrologic <br />conditions are further evaluated. The projected dewatering wells are designed to be completed between <br />50 and 100 feet below the pit floor to dewater the lower portion of the pit. An examination of the cross <br />section illustrates the fact that the total cone of influence of the dewatering wells on the north side of the <br />proposed pit will be several miles from Wilson Creek and any beneficial use wells near Wilson Creek. In <br />addition, the KM layer (an aquiclude) precludes any impact of the dewatering on the upgradient wells in <br />Wilson Creek. Finally, the dip of the KM bed and the Trout Creek sandstone top is to the north and any <br />ground water flow would be down dip away from Wilson Creek. <br />In the Little Collom X pit, any perched groundwater present in the shallow mining sequence in the Little <br />Collom X pit is expected to be of very limited quantity and areal extent. The coal seams and associated <br />rocks to be affected by mining outcrop along the adjacent valley walls and have been removed from the <br />valley areas by erosion. Perched aquifers in a similar setting have been encountered in the existing <br />Colowyo operations, and these aquifers drain rapidly. Once drained, they do not produce any significant <br />water during mining into the current pits. <br />Pit Inflow and Pit Surface Water Recharge Impacts <br />Five springs within Little Collom Gulch will be eliminated by the mining operations: SPRLC -01, <br />SPRLC -02, SPRLC -03, VI I, and V29. Two of those, VI I and V29, were identified by previous <br />investigations, but proved to be dry during baseline monitoring efforts. Little Collom Gulch had no flow <br />during the 18 months of baseline :monitoring; therefore, elimination of these springs will have no <br />measurable effect on streamflow. <br />Collom — Rule 2, Page 135 Revision Date: 9/28/11 <br />Revision No.: PR -03 <br />