2010-06-28_REVISION - C1981019 (2)

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Creek watershed that enters below the upstream station may be responsible for a good part of this difference. However, neither TDS plot on Figure 4-3 shows any increasing trend with time, suggesting that the mine's presence is not the cause of this difference. There are no similar monitoring stations near the West Pit reclaimed areas that would allow a side-by-side comparison of upstream and downstream conditions. However, since the mining and reclamation techniques are the same as for the East Pit reclaimed lands discussed above, it is reasonable to conclude that the same impacts would exist at the West Pit reclaimed areas, that is, no significant impact on surface water quality or quantity. The results of the modeling and the actual field measurements confirm the conclusion in the original permit application that the mine would have little discernable impact on the surface water hydrology. 4.3 Groundwater Impacts As described above, the groundwater affected by the mine permit area is essentially the limited and hydrologically insignificant locally perched water zones in the rock strata overlying the coal seams. Contact between the mine and the underlying Trout Creek Sandstone is limited by strata thickness and the presence of at least one impervious layer near the base of the Williams Fork Formation. In Section 2.04.7 of the application (p. 2.04.7-27), it is anticipated that net infiltration within the reclaimed lands will not change appreciably from the premining condition, and will remain a very small fraction of the incipient precipitation, leaving only limited opportunity for deep percolation once reclamation is complete. 4.3.1 CDRMS Observed Spoil Seeps There are five surface seeps of interest identified by CDRMS staff as "spoil seeps", adjacent to but outside the reclamation areas associated with this application. The locations of these seeps are presented on Exhibit 1, Phase III Bond Release. Although they are referred to as "spoil seeps", the four along the eastern edge of the permit boundary in Sections 11 and 14 are on undisturbed land outside the pit limits, but just downhill of the toe of out of pit spoil areas. These seeps are described as sporadic and seasonal, with flow quantities too small to measure, but enough to create a wet area on the surface. They are likely releasing shallow groundwater from recent snow melt or precipitation events. This is very similar to the descriptions of similar local seeps in the original permit application. Since these four seeps on the eastern edge of the permit area are all well above the elevation of the nearby pit floor to the west, and are also on areas not disturbed by mining, they are most likely remnants of such previously described seeps from locally perched wet zones. Their local recharge zones must have been quite small because they were apparently not affected by the nearby pit a few hundred feet to the west at its closest point. This suggests that the recharge source for Phase l// Bond Release Application 15