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Ground water <br />Several possible effects to the ground water system have been identified. <br />Dewatering and uotentiometric drawdown in bedrock units <br />Dewatering will occur in the Wadge overburden, possibly out as faz as the outcrop around the <br />margins of the basin. Dewatering will occur in the Twentymile sandstone above the area of <br />active mining. Drawdown will occur in the Trout Creek sandstone if communication with the <br />mine is established through fault zones. Monitoring data indicates no impact to the Trout <br />Creek sandstone to date. <br />Diminution of bedrock dischazge to alluvium and surface streams <br />Gradient reversal due to mining could cause a decrease in natural dischazge to alluvium and <br />streams. This would persist for approximately 360 years; that is, until potentiometric levels <br />recover to pre-mining conditions. In the past, discharge of mine water to the streams more <br />than offset this loss. Recently, however, mine water has been used in underground operations, <br />with a loss estimated at approximately 0.02 cfs in Fish Creek (approximately 0.5% of Fish <br />Creek flows).8 <br />Degradation of Wadee overburden water <br />Only the Wadge overburden aquifer is predicted to be degraded with regard to water quality. <br />Estimates indicate that degraded water will persist for 23,000 years. Conductivity of degraded <br />water is estimated at 4,000-7,000 umhos/cm. Areas immediately downgradient will be <br />affected to a greater degree due to the close proximity to the source (mine workings). Due to <br />dilution and dispersion, water quality will generally improve as the distance from the mine <br />workings increases. Wadge overburden water is not presently used in the Twentymile Pazk <br />basin. <br />Degradation of alluvial water quality in Fish Creek <br />This water will move downgradient to the natural dischazge points along Fish Creek. Alluvial <br />aquifers aze rechazged mainly by stream flows during high flow conditions and to a lesser <br />degree, bedrock dischazge. Given the small amount of estimated dischazge, this degraded <br />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 <br />subsidence and effects to ground water quantity can be summazized as follows: <br />a PAP, page 2.05-191 <br />13 <br />