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Possible hydrologic impacts on groundwater quantity by the underground mining operation <br />include: <br />1. The effect of subsidence and the related dewatering of the area, and <br />2. The effect of additional water added to the Colorado alluvial system from mine <br />inflow being discharged through the mine and to the surface. <br />Groundwater Quantity: Effect due to Subsidence <br />Groundwater quantity will initially be affected due to subsidence activity in the Rapid Creek <br />basin. The effect will be temporary in nature and provide no material damage to downstream <br />users. To quote from the Brooks study of 1986 on the operation's potential impact to the area, <br />"Mining coal in the Mesaverde Group temporarily will dewater the rock adjacent to the <br />underground mine This rock will become rubblized and increase the permeability of the rock <br />thus increasing the flow of groundwater into the area." Inflow in the mine is expected to <br />increase as a result with a secondary effect of lowering the potentiometric surface temporarily. <br />Water levels should return to pre - mining levels after the underground mine is sealed, with <br />saturation occurring after several years. The mine utilized limited extraction methods in the <br />Cottonwood and Rapid Creek areas. <br />Past monitoring of the alluvium of Rapid and Cottonwood Creeks has not detected any <br />significant depletion of alluvial water in either creek system, and no significant depletion is <br />anticipated. <br />There is no beneficial use of the groundwater in the mine permit area or vicinity. Mine inflow <br />quantity has been documented in past Annual Hydrology Reports. It has been demonstrated that <br />most of the mine inflow waters originate in the new faces of virgin coal seams. As these seams <br />are mined, the coal seam aquifer is dewatered. New areas of the mine have a higher inflow rate <br />than older, developed ones, which dry out after the area has been developed. Additional water <br />originates from the Mesaverde sandstone lenses as they are dewatered by mining activity <br />combined with subsidence. <br />The operator has committed to a mitigation contingency plan for downstream users should they <br />be effected by subsidence. <br />Groundwater Quantity: Effect on the Colorado River Alluvial Aquifer <br />Water quantity in the alluvium of the Colorado River aquifer is minimally affected by the mine <br />operations. The quantity of surface water and groundwater in the Roadside North and South <br />Portal facility areas and adjacent areas will not be adversely affected due to the recycling nature <br />of the ground and surface waters in the alluvial valley floor. Mining did not occur beneath the <br />Colorado River alluvial valley floor. Groundwater inflows to the South Mine workings <br />discharge by gravity flow through a dewatering pipe near the reclaimed North Decline, at <br />Discharge Site 016, into the Colorado River. Approximately 0.7 cfs of mine water is discharged <br />into the Colorado River. <br />Permit Revision No. 5 33 July 10, 2012 <br />