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minimization. During the period of active use, minor intermittent seepage was <br /> observed from the rock underdrains beneath CRDA-1,and from widely scattered seep <br /> areas on the CRDA-1 and CRDA-2 bench outslopes. <br /> Groundwater Quantity <br /> Possible hydrologic impacts on groundwater quantity by the underground mining <br /> operation include: <br /> I. 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 <br /> Creek basin. The effect will be temporary in nature and provide no material damage <br /> to downstream users. To quote from the Brooks study of 1986 on the operation's <br /> potential impact to the area, "Mining coal in the Mesaverde Group temporarily will <br /> dewater the rock adjacent to the underground mine. This rock will become rubblized <br /> and increase the permeability of the rock thus increasing the flow of groundwater into <br /> the area." Inflow in the mine is expected to increase as a result with a secondary effect <br /> of lowering the potentiometric surface temporarily. Water levels should return to <br /> pre-mining levels after the underground mine is sealed,with saturation occurring after <br /> several years. The mine utilized limited extraction methods in the Cottonwood and <br /> Rapid Creek areas. <br /> Past monitoring of the alluvium of Rapid and Cottonwood Creeks has not detected <br /> any significant depletion of alluvial water in either creek system, and no significant <br /> depletion is anticipated. <br /> There is no beneficial use of the groundwater in the mine permit area or vicinity. Mine <br /> inflow quantity has been documented in past Annual Hydrology Reports. It has been <br /> demonstrated that most of the mine inflow waters originate in the new faces of virgin <br /> coal seams. As these seams are mined,the coal seam aquifer is dewatered. New areas <br /> of the mine have a higher inflow rate than older, developed ones,which dry out after <br /> the area has been developed. Additional water originates from the Mesaverde <br /> sandstone lenses as they are dewatered by mining activity combined with subsidence. <br /> The operator has committed to a mitigation contingency plan for downstream users <br /> should they be effected by subsidence. Minor Revision No. 88, Approved October <br /> 10, 2022, added Appendix 7-4 (Vol. 2) to the permit. Appendix 7-4 is a Compliance <br /> Order on Consent with the Colorado Division of Water Resources for an alternate <br /> water supply to Cottonwood and/or Rapid creeks. At the request of the Colorado <br /> Division of Water Resources, Office of the State Engineer and the Division Engineer <br /> for Water Division 5 (together "DWR"), SCC had a study performed to investigate <br /> 36 <br />