2013-04-10_PERMIT FILE - C1981019 (82)

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RULE 2 PERMITS Based on the above, there would be minimal dilution of any spoil spring water that may reach Collom Gulch. As noted previously, there may some dilution of the spoil spring water before it reaches Collom Gulch due to the long transit time as it flows down Little Collom Gulch. Combining transit time with the minimal time for the spoil aquifer to start to flow down Little Collom Gulch, a total of at least 150 years from the cessation of the dewatering wells would pass before any spoil spring water would reach Collom Gulch in Section 13, T. 4 N., R. 94W. Finally, this does not take in to account any infiltration of the spoil spring water into the underlying bedrock as would be expected in the upper reaches of Little Collom Gulch. The probable impact of the seepage from the highwall to the non - saturated portion of the area down gradient of Collom Lite mining area is considered minimal. In addition, spoil spring discharges will be unlikely due to the geological characteristics of the Collom Lite permit area. Since the dip of the geologic units is greater than the topographic gradient to the north, any pitwall seepage will follow the geologic units to a depth, which is greater than that found in the pitwall. In addition, since the most probable discharge point for potential spoil aquifer is at the intersection of Little Collom Gulch with the northern pitwall (elevation 7275 feet), all pitwall discharges will be below this elevation and thus below the Little Collom Gulch drainage to create spoil springs. Using the above spoil aquifer and the pit seepage calculations above, the time for a spoil aquifer to reach the most probable discharge point has increased slightly due to the pit seepage. Groundwater accumulating in the pit backfill and flowing into the deeper bedrock units on the downdip side of the reclaimed pit would likely have the same characteristics as the water in the Streeter Fill well or the Streeter pond or in similar spoil springs (Williams and Clark, 1994). Analytical data for these sampling points are summarized on Table 2.04.7 -49. The above information suggests that it is possible that a reclaimed pit aquifer (if one develops) will flow entirely into the undisturbed strata and that there will be no or limited discharge into the surficial valley fill from the reclaimed pit. Potential Surface Water Quantity Impacts As described above, Little Collom Gulch is ephemeral, and showed no evidence of surface flow during 18 months of baseline monitoring. Elimination of springs within Little Collom Gulch will therefore have no measurable effect on surface water quantity in Little Collom Gulch. There may be an effect on peak flows in the West Fork of Jubb Creek, due to the elimination of recharge to three springs adjacent to the Collom Lite pit, but this effect is 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. Other than those directly eliminated by the pit, no springs are likely to be affected by the Little Collom X pit. Potential Surface Water Quality Impacts Potential impacts to the surface water quality from the proposed Collom Lite and Little Collom X mining operations are considered here. As described above, Little Collom Gulch is ephemeral, and showed no evidence of surface flow during 18 months of baseline monitoring. There is therefore no basis on which to determine relative changes in surface water quality for Little Collom Gulch. Potential mining impacts will be limited to the shallow valley fill groundwater regime, discussed elsewhere, rather than surface water. Collom — Rule 2, Page 140 Revision Date: 9/28/11 Revision No.: PR -03