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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 a[ <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 <br />indicate that degraded water will persist for 23,000 years. Conductiviry of degraded water is estimated at <br />4000-7000 umhos/cm. Areas immediately downgradient will be affected to a greater degree due to the <br />close proximity to the source (mine workings). Due to dilution and dispersion, water quality will <br />generally improve as the distance from the mine workings increases. Wadge overburden water is not <br />presently used in the Twentymile Park basin. <br />Degradation of alluvial water aualiri in Fish Creek <br />This water will move downgradient to the nattual dischazge points along Fish Creek. Alluvial aquifers are <br />recharged mainly by stream flows during high flow conditions and to a lesser degree, bedrock discharge. <br />Given the small amount of estimated discharge, this degraded water will easily be diluted by upstream <br />flows. <br />Subsidence imoacts to bedrock aquifer water ouanti <br />Although the applicant presents no site specific information, the predicted consequences of subsidence and <br />effecu to ground water quantity can be summazized 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 />Subsidence impacu to alluvial water auantiri <br />Alluvial waters should not be impacted due to mining and subsidence, due to the presence of a 500-600 <br />foot thick marine shale above the mined Wadge seam which acts as an aquiclude and minimizes the <br />disruption in the near surface. Previous subsidence along Fish Creek in the Western Mining District <br />recorded only minimal changes in the water levels in the alluvial aquifer of Fish Creek. <br />Subsidence impacts to ground water quality <br />The mine predicu that subsidence fracturing could cause a new hydraulic connection between bedrock <br />uniu with different quality. However, the applicant states that monitoring data recorded does not indicate <br />any substantial intercommunication of bedrock or alluvial aquifers. <br />Surface water <br />Several possible effects on the surface water system have been identified <br />C:U H B\C82066\RN03\RN03FIND.doc <br />14 <br />