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The Division has evaluated the detailed hydrology information to determine the probable effects of the mining operation on the prevailing hydrologic balance. The potential effects of the mining operation on the prevailing hydrologic balance are minimal. There is a slight possibility that flow in Trout Creek would be decreased and flow in Middle Creek increased if an unrecorded fault with high transmissivities is encountered. This is highly unlikely because of the horst and graben geology and the nontransmissive character of each of the faults observed thus far as was discussed previously in Section VI - Ground Water Hydrology. Mining during the initial permit term did not encounter such an unrecorded fault, and proposed mining in the second permit term does not entail any advance mining but rather retreating back and pulling pillars. Therefore, the possibility of decreasing Trout Creek flow and increasing Middle Creek flow is highly unlikely. As discussed previously in Section V - Surface Water Hydrology, the possible hydrologic impacts to springs tributary to Middle Creek and the potential adverse effects to the prevailing hydrologic balance of Trout Creek are minimal. The effects have been minimized by the operation for three reasons: 1. Underground development waste will be deposited into worked-out pillar areas or in other permitted areas; 2. The dip of the strata and the mine workings is away from Trout Creek; and 3. Over 80% of the mine workings are above the piezometric surface. Also, all surface drainage from the disturbed area is routed through the sedimentation pond, thereby minimizing the affects to Trout Creek. Therefore, the Division concludes that there will be no adverse effects from the mining operation due to leachate development from waste material, mine drainage, or dewatering the alluvial aquifer. A cumulative hydrologic assessment of effects of coal mining on the Yampa River Basin was prepared for the Division by the consulting firm of Kaman Tempo in 1982. The report stated, "The Apex No. 2 Mine appears to have negligible off-site impacts to the hydrologic balance." The Division has evaluated the potential impacts of the Apex No. 2 Mine to the hydrologic balance in more detail since the Kaman Tempo study. The most recent cumulative hydrologic impact statement was performed for the Eckman Park Mine Complex (Eckman Park Mine, Mine No. 1, and Mine No. 2) Permit C-81-071 in 1987. This additional hydrologic data analysis confirms the statements of the Kaman Tempo study that there will be negligible off-sites impacts to the hydrologic balance. Even though the potential for impact is minimal, Sunland continues to monitor mine inflows, and surface and alluvial water flows for both quality and quantity of water to substantiate the predictions (see page 65.06 of the permit application). -13-