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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 streams. <br />This would persist for approximately 360 years until potentiometric levels recover to pre-mining <br />conditions. Dischazge of mine water to the streams will more than offset this loss, which is estimated <br />at approximately 0.02 cfs in Fish Creek. <br />Degradation of Wadge overburden water <br />Only the Wadge overburden aquifer is predicted to be degraded with regazd to water quality. <br />Estimates indicate that degraded water will persist for 23,000 years. Conductivity of degraded water is <br />estimated at 4,000-7,000 umhos/cm. Areas immediately downgradient will be affected to a greater <br />degree due to the close proximity to the source (mine workings). Due to dilution and dispersion, water <br />quality will generally improve as the distance from the mine workings increases. Wadge overburden <br />water is not presently used in the Twentymile Pazk basin. <br />D~adation of alluvial water quality in Fish Creek <br />This water will move downgradient to the natural dischazge points along Fish Creek. Alluvial aquifers <br />aze rechazged mainly by stream flows during high flow conditions and to a lesser degree, bedrock <br />dischazge. Given the small amount of estimated dischazge, this degraded water will easily be diluted <br />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 <br />and effects to Bound water quantity can be summarized as follows: <br />a) Increased permeability above mined azea, especially within 300 feet of the mine roof. <br />b) Cracking, of limited depth, of the ground surface above the mined area. <br />Subsidence impacts to alluvial water quantity <br />Alluvial waters should not be impacted due to mining and subsidence, due to the presence of a 500- <br />600 foot thick marine shale above the mined Wadge seam which acts as an aquiclude and minimizes <br />the disruption'in the neaz surface. Previous subsidence along Fish Creek in the Western Mining <br />District 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 predicts that subsidence fracturing could cause a new hydraulic connection between bedrock <br />units with different quality. However, the applicant states that monitoring data recorded does not <br />indicate any substantial intercommunication of bedrock or alluvial aquifers. <br />Compliance with Basic Standazds for Ground Water <br />(Regulation 41 of the Colorado Water Quality Control Commission) <br />Section 4.05.13(1) of the Regulations require the establishment of one or more ground water points of <br />compliance (wells) for an operation which has the potential to negatively impact the quality of ground <br />water. The Wadge overburden and the Twentymile Sandstone are the rivo aquifers most likely to be <br />11 <br />