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1 1 1 t 1 1 pre-mining simulation. The differences in the water levels were considered the water level changes resulting from mining. These changes for each simulation are summarized below and in the referenced appendices. Water level changes resulting from each scenario were categorized into risk categories. 4.6.1 Ground Water Level Changes During Mining Ground water level changes during mining were simulated based on a worst-case scenario in which the entire mined area was mined and dewatered simultaneously. In actualit}', mining will occur in phases over more than 30 yeazs, and consequently, water level impacts will be concentrated in one region while that azea is mined. Lazge-scale dewatering will never occur over the entire mined azea simultaneously. The mined azeas will ultimately include low permeability barriers at their edges, constructed with compacted shale slopes. These barriers will help to mitigate ground water level changes occurring outside of the mined area. To account for these barriers, simtlations were performed in which the entire mined areas are dewatered within the barriers. However, during mining of the fringes of the pits, the barriers will not be installed, and dewatering will occur for part of the mining operation while the barriers are not in place. In order to account for this type of operation, aworst-case scenazio simulation was performed in which the entire mine is dewatered without any barriers in place. The findings of these simulations are summarized bel~aw. Modeled water level elevation contours during mining with the barrier installed aze: presented in Appendix R, and water level drawdown contours are presented in Appendix S. As noted on these maps, water level drawdowns aze greatest inside the mine, as expected. Outside of the mine, water levels aze slightly lower than before mining in some locations and aze slightly higher than before mining in other locations. Generally, water level changes are limited to azeas sout:i of the South Branch; the South Branch and St. Vrain River buffer the water level impacts north of the streams. The exception to this is water level impacts resulting from the pit located north of the South Branch to be mined during Phase II of the amended application (shown and the Phase II pond on Figure 1). During mining of this pond, water level impacts could occur north of the South Branch. Along the _17_ lti.cdn/1-lirvipwi.I~~nr'm/rs, /ur.