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Gradient reversal due to mining could cause a decrease in natural discharge to alluvium and streams. This would persist for approximately 360 years until potentiometric levels recover to pre-mining conditions. Discharge of mini watu oischarge iv [I;e iiicaia'~~'lll mOfC than Jii3e[ ihti loss, winch is animated at approximately .03 cfs in Fish Creek. Dzgrada[ion of Wadge overburden water Only the Wadge overburden aquifer is predicted [o be degraded with regard to water quality. Estimates indicate that degraded water will persist for 23,000 years. Conductivity of degraded water is estimated at 4000-7000 umhosfcm. Areas immediately downgradient will be affected to a greater degree due to the close proximity to [he source (mine workings). Due to dilution and dispersion, water quality will generally improve as the distance from the mine workings increases. Wadge overburden water is not presently used in the Twentymile Park basin. Deeradation of alluvia! water quality in Fish Creek Deeraded Wadge overburden water will move downgradient to [he natural discharge points along Fish Creek. Alluvial aquifers are recharged mainly by stream flows during high flow conditions and to a lesser degree, bedrock discharge. Given the small amount of estimated discharge, this degraded water will easily be diluted by upstream flows. Expansion of the mine plan into the Northern Mining District will result in subsidence of portions of Fish Creek and its associated alluvial valley floor. Twentymile Coal Company predicts pooling of water in subsidence troughs along Fish Creek where it overlies the longwall panels. This pooling or ponding of water should not cause any significant changes in alluvial water quality. Subsidence impacts to bedrock aquifer water guantiri Although the applicant presents no site specific information, the predicted consequences of subsidence and effects to ground water quantity can be summarized as follows: a) Increased permeability above mined area, especially within 300 feet of the mine roof. b) Cracking, of limited depth, of the ground surface above the mined area. Subsidence impacts [o alluvial water quantity Alluvial waters should not be impacted due to mining and subsidence, due to the presence of a 500-600 foot thick marine shale above the mined Wadge seam which acts as an aquiclude and minimizes the disruption in the near surface. Previous subsidence along Fish Creek in the Western Mining District recorded only minimal changes in the water levels in the alluvial aquifer of Fish Creek. Subsidence of approximately 17,000 feet of Fish Creek may cause minor or transient loss of alluvial water if cracks in the bedrock that underlies the alluvium develop following subsidence. Experience along Foidel Creek indicates cracks in communication with the alluviaum should develop only in areas where the creek channel passes over exposed bedrock. Most of the area to be undermined and subsided in the Northern Mining District consists of alluvium in contact with the Lewis Shale or other shale formations which have not shown surface cracking due to subsidence. Any surface cracks that do form fill and seal within a few weeks . Interruption of flow would be temporary and transient in nature and would not be ofa volume that would impact irrigation use downstream. Subsidence impacts to ground water quality The mine predicts that subsidence fracturing could cause a new hydraulic connection between bedrock units with different quality. However, the applicant states that monitoring data recorded does not indicate any substantial intercommunication of bedrock or alluvial aquifers. C:\JHB\C82056\PROS1PR05 FINDINGS 62800.doc 13