2011-03-17_REVISION - C1981008 (2)

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No structures are left in place on any of the areas covered by this release application. The post-mine land use is irrigated and dryland pasture. 3. Topsoil Thickness Topsoil was replaced to the thicknesses shown by the sample points on Map R-2, in accordance with the mine permit. This was also addressed in the Phase 2 bond release from 2008. 4. Final Topography and Drainage Patterns The final topography of the original site has been restored to approximate original contour within the reclaimed areas. The enclosed Map R-2 shows this topography. The reclaimed areas all drain to the south to Calamity Draw. Some of the surface draining off of Area 3 will drain to Pond 007 before passing into Calamity Draw. 5. Surface and Ground Water The potential surface and ground water impacts from the New Horizon #2 Mine were detailed in Section 2.05.6(3) of the permit, under the Probable Hydrologic Consequences section. The main potential impact is the possible infiltration of water into the replaced overburden leading to the degradation of pyrite, and the subsequent effect this can have on the dissolved solids and pH of the water. A) Impact on Ground Water Rights Ground water rights within the vicinity of the New Horizon #2 Mine (2 mile radius) are identified in Appendix 2.04.7-1 of the permit. A total of 29 ground water rights have been been identified. All monitoring wells installed by the permittee and domestic wells within the surrounding area are shown on Map 2.04.7-1-A. No wells are within the release area. Of the 29 water rights within the surrounding are, 27 wells have intakes too deep to be affected by the pit pumping induced drawdowns in the overburden aquifer. These wells are installed in the Burro Cantion Formation, which is below the Dakota coals to be mined. Significant shales separate the coals from the strata of the wells. Two righted wells W-009 and W041 have intakes close to the location of the bottom of the mine pit. The wells area located approximately 2,300 feet east of New Horizon #2. At the eastern boundary of New Horizon #2, mining will only extend 10 feet below the water table. Therefore, drawdown impacts to these wells are expected to be small. The wells are righted for irrigation water use. This area has been mined and reclaimed over 10 years ago and there has not been any problem identified with these wells. B) Impact of Spoil Material on Ground Water Flow and Recharge The Phase 3 release areas have been fully reclaimed for approximately 10 years. The potential long term impact on ground water flow and recharge is the change in permeability of the spoil material placed as backfill. The only vertical and horizontal permeability change that will have occurred in the backfill will be of an increase in permeability. This is due to mining techniques. The resaturation time period for ground water will be reduced by the irrigation recharge in the Irrigated Pasture areas and overall by the increased permeability in SL-12 CURRENT 11MAR11.wpd 40