2011-08-09_REVISION - C1981019 (10)

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• • • RULE 2 PERMITS influence for each well to interfere with another within 500 feet and allow for the water level to be dropped around the pit in a reasonable timeframe. The wells well be placed within approxiamtely 500 feet of the projected pit outline and within the upslope area of the pit. This will allow total dewatering of the first cuts. After the cuts are mined, then dewatering will cease as the pit floor will be above the anticpated saturated water level( -7150 feet amsl) Thus during the dewatering, since there are no beneficial wells (other then those owned and /or controlled by Colowyo) within a two mile radius of the northen pit limit of Collom Lite, there will be no impact on any non - Colowyo well. Minor pumping of water entering the pit from draining of the perched aquifers from the south may be required to remove this water to facilitate mining. In the Little Collom X pit, any perched groundwater present in the shallow mining sequence in the Little Collom X pit is expected to be of very limited quantity and areal extent. The coal seams and associated rocks to be affected by mining outcrop along the adjacent valley walls and have been removed from the valley areas by erosion. Perched aquifers in a similar setting have been encountered in the existing Colowyo operations, and these aquifers drain rapidly. Once drained, they do not produce any significant water during mining into the current pits. Pit Inflow and Pit Surface Water Recharge Impacts Five springs within Little Collom Gulch will be eliminated by the mining operations: SPRLC -01, SPRLC -02, SPRLC -03, V11, and V29. Two of those, V11 and V29, were identified by previous investigations, but proved to be dry during baseline monitoring efforts. Little Collom Gulch had no flow during the 18 months of baseline monitoring; therefore, elimination of these springs will have no measurable effect on streamflow. The Collom Lite pit is likely to be within the watersheds for springs V1, V10, and V32 (West Fork of Jubb Creek). These springs collectively produce about 0.024 cfs during September, during which monitoring location WFJC was dry, indicating that the spring flow reinfiltrates into the valley fill, or is captured in stock ponds before reaching the monitoring point. The springs contributed about 0.042 cfs in May 2006 to the West Fork of Jubb Creek. Stream flow was measured in May 2005 as 0.10 cfs. No conclusive estimate of the percentage contributed by the springs can be made given the likely difference between hydrologic conditions in those two years. Considering that 0.024 cfs was lost to valley fill or ponds during September, it appears that the contribution of V1, V10, and V32 to the peak flow at WFJC could be considerably less than the 42 percent implied by a year -to -year comparison. At monitoring point CJC, the May 2005 discharge was 0.15 cfs, implying that the affected springs contribute 28 percent of the flow at that location. Since much of the recharge is from undisturbed areas outside of the Collom Lite pit, the probable reduction is likely to be less than half of this amount and not expected to be measurable or statistically significant. Once the mining has been completed and the pit has been saturated, the contributions to surface water from springs originating from infiltration into the Collom Lite pit would return to normal. Collom Lite Pit Hydrology — The Collom Lite pit will have a reclaimed surface area of approximately 880 acres and a pit bottom that inclines predominantly toward the north. The low point in the reclaimed pit topography will be at its intersection with the valley of Little Collom Gulch, at an elevation of approximately 7,275 feet amsl. Resaturation of the reclaimed pit backfill will occur from confined Collom — Rule 2, Page 135 Revision Date: 8/5/11 Revision No.: PR -03