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projected. The subsidence effects from the f=ive-year mining plan are not ex- pected to change the pre-mining and post-mining use for the struc- tures and renewable resource lands within and adjacent to the proposed Permit Area. All existing structures and proposed mine facilities are located outside the area of mining-related sub- sidence. Undeveloped land constitutes the majority of the existing land use within the areas potentially subject to mining-related surface subsidence. Rangeland, wildlife habitat, surface water resource land and subsurface water resource land are also located within the area potentially subjected to subsidence. Based upon the maximum surface subsidence of 19 feet, the impacts on surface water resources will be negligible. Flow gradients on unnamed tributaries to Alkali Creek and th2 Colorado River will decrease less than O.lo (0.001) in areas where the existing channel gradients are 0.15 to 0.20. The steep gradients and clayey soils will prevent increased recharge of surface waters into the ground water system. However, in all cases, the pre-mining and post- mining land use is expected to remain the same for renewable resource lands subjected to mining-related subsidence. The worst possible consequence analysis of subsidence indicates that the development of sinkhole subsidence and slope instability are low probability events. NCIG has outlined proposed mitigation measures in the unlikely event that sinkhole subsidence occurs or slope instability occurs. Sinkhole subsidence is not expected to occur because no down dip movement of the gob is expected. The forces acting to move the gob down dip probably will not be sufficient to overcome the forces resisting gob movement. Further, ramp pillar stumps and panel pillar stumps will serve to restrict any down dip movement of the gob. NCIG - Coal Ridge #1 4-90 ABC/1145/910509 • • •