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Mine (2.07.6(2)(b)). <br />3. The assessment of the probable cumulative impacts of all anticipated coal mining in the general area on the <br />hydrologic balance, as described in 2.05.6(3), has been made by the Division. This assessment entitled <br />"Yampa River CHIA" (revised March 2000) is available for inspection at the offices of the Division. <br />4. A brief summary of the Probable Hydrologic Consequences of the Foidel Creek Mine follows: <br />Ground water <br />Several possible effects to the ground water system have been identified. <br />Dewatering and notentiometric drawdown in bedrock units <br />Dewatering will occur in the Trout Creek Sandstone,Wadge overburden, and Twentymile Sandstone. <br />Monitoring data have verified this dewatering has occurred and the depression of the potentiometric surfaces of <br />these hydrostratigraphic units in the vicinity of the mine. <br />Diminution of bedrock discharge to alluvium and surface streams <br />Gradient reversal due to mining could cause a decrease in natural discharge to alluvium and streams. This <br />would persist for approximately 360 years until potentiometric levels recover to pre-mining conditions. <br />Discharge of mine water discharge to the streams will more than offset this loss, which is estimated at <br />approximately .02 cfs in Fish Creek. <br />Degradation of Wadge overburden water <br />Only the Wadge overburden aquifer is predicted to be degraded with regard to water quality. Estimates indicate <br />that degraded water will persist for 23,000 years. Conductivity of degraded water is estimated at 4000-7000 <br />umhos/cm. Areas immediately downgradient will be affected to a greater degree due to the close proximity to <br />the source (mine workings). Due to dilution and dispersion, water quality will generally improve as the distance <br />from the mine workings increases. Wadge overburden water is not presently used in the Twentymile Park <br />basin. <br />Degradation of alluvial water quality in Fish Creek <br />Water will move downgradient to the natural discharge points along Fish Creek. Alluvial aquifers are recharged <br />mainly by stream flows during high flow conditions and to a lesser degree, bedrock discharge. Given the small <br />amount of estimated discharge, this degraded water will easily be diluted by upstream flows. <br />Subsidence impacts to bedrock aquifer water quantity <br />Although the applicant presents no site specific information, the predicted consequences of subsidence and <br />effects to ground water quantity can be summarized as follows: <br />a) Increased permeability above mined area, especially within 300 feet of the mine roof. <br />b) Cracking, of limited depth, of the ground surface above the mined area. <br />12