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TDS inflows aze thought to indicate longer residence time and reactive time with soluble <br />minerals in the transmitting aquifer. These inflows maythus represent the dewatering of <br />overlying and underlying aquifers, and perhaps the coal seams, whose ultimate source of <br />rechazge cannot readily be determined. <br />The impacts of depleting ground water in overlying and underlying aquifers were <br />predicted to be minhnal due to impermeability of the formations. Equilibrium has been <br />established between the mine workings and the overlying and underlying strata. As mine <br />inflows now dischazge to surface waters, any reduction in pre-mining groundwater chazge <br />to surface waters, or infiltration of surface waters into mine workings, is likely offset by <br />dischazge from the mine portals. <br />All underground mines that induce subsidence have the potential to increase mine <br />inflows, particulazly if the subsidence occurs within a significant source of water (e.g., <br />stream, pond, formation strata or alluvial aquifers). However, coal mine subsidence does <br />not seem to be or have been a source of significant inflows into the North Thompson <br />Creek Mines. Subsidence studies indicate that long-wall mining collapse migration up <br />into overburden was not extensive. There was no significant mine inflow neaz areas that <br />were mined by longwall and pillar extraction while the mine was operational. This can be <br />attributed to low transmissivity in tight overburden and interburden formations, to the fact <br />that vertical migration of collapse was arrested in short distances and did not establish <br />hydraulic communication with significant aquifers, and to the fact that these mine azeas <br />aze not under perennial stream valleys, but under steep hillslopes. <br />There is a potential for the formation of acidic and toxic mine waters. The applicant has <br />submitted analyses of the coals, roof, and floor strata. The analyses of the roof and floor <br />materials performed by the Soils Laboratory of Colorado State University (Appendix 3-I <br />of the PAP) indicate that these units contain insufficient carbonate minerals to buffer the <br />iron sulfide (e.g., pyrite) contained in these strata. These analyses indicate that these strata <br />are acid-forming and potentially toxic. Ground water quality in overlying and underlying <br />aquifers maybe degrading through vertical communication of strata caused by faults and <br />fractures. Degradation of water quality would result from prolonged exposure of water to, <br />host formations, fractured roof strata, and the exposed coal strata (roof, floor, face, ribs, <br />gob, etc). <br />The depletion of ground water from aquifers may affect the discharge of over and <br />underlying aquifers to springs and seeps, and to the hydrologic regime of the aquifer(s). <br />The applicant has identified (PAP) only two springs, SP-1 and SP-2, in the permit and <br />adjacent areas. Any groundwater denied these springs would be released from the mine <br />portals. Recharge of deep aquifers into the Piceance Creek structural basin might be <br />diminished (due to loss of hydraulic head above the mines), but pooled mine water <br />becomes a source of rechazge to all hydraulically-connected seams of lower piezeometric <br />levels. Such is not likely at the North Thompson Creek Mines. Piezeometric surfaces of <br />ground water about the mined azeas aze higher than the mine portals. There is likely little, <br />if any, rechazge into these aquifers from the flooded mines. If there is any, such water <br />17 <br />