2013-10-07_REVISION - C1981025 (8)

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represent the dewatering of overlying and underlying aquifers and perhaps the coal seams, whose ultimate source of recharge cannot readily be determined. The impacts of depleting ground water in overlying and underlying aquifers were predicted to be minimal due to impermeability of the formations. Equilibrium has been established between the mine workings and the overlying and underlying strata. As mine inflows now discharge to surface waters, any reduction in pre- mining groundwater charge to surface waters or infiltration of surface waters into mine workings, is likely offset by discharge from the mine portals. All underground mines that induce subsidence have the potential to increase mine inflows particularly if the subsidence occurs within a significant source of water (e.g. stream, pond, formation strata or alluvial aquifers). However, coal mine subsidence does not seem to be or have been a source of significant inflows into the North Thompson Creek Mines. Subsidence studies indicate that longwall mining collapse migration up into overburden was not extensive. There was no significant mine inflow near areas that were mined by longwall and pillar extraction while the mine was operational. This can be attributed to low transmissivity in tight overburden and interburden formations, to the fact that vertical migration of collapse was arrested in short distances and did not establish hydraulic communication with significant aquifers, and to the fact that these mine areas are not under perennial stream valleys, but under steep hillslopes. There is a potential for the formation of acidic and toxic mine waters. The applicant has submitted analyses of the coals roof and floor strata. The analyses of the roof and floor materials performed by the Soils Laboratory of Colorado State University (Appendix 3-I of the PAP) indicate that these units contain insufficient carbonate minerals to buffer the iron sulfide (e.g. pyrite) contained in these strata. These analyses indicate that these strata are acid-forming and potentially toxic. Ground water quality in overlying and underlying aquifers may be degrading through vertical communication of strata caused by faults and fractures. Degradation of water quality would result from prolonged exposure of water to host formations, fractured roof strata and the exposed coal strata (roof, floor, face, ribs, gob, etc). The depletion of ground water from aquifers may affect the discharge of over and underlying aquifers to springs and seeps, and to the hydrologic regime of the aquifer(s). The applicant has identified (PAP) only two springs, SP-1 and SP-2, in the permit and adjacent areas. Any groundwater denied these springs would be released from the mine portals. Recharge of deep aquifers into the Piceance Creek structural basin might be diminished (due to loss of hydraulic head above the mines), but pooled mine water becomes a source of recharge to all hydraulically-connected seams of lower piezeometric levels. Such is not likely at the North Thompson Creek Mines. Piezeometric surfaces of ground water about the mined areas are higher than the mine portals. There is likely little, if any, recharge into these aquifers from the flooded mines. If there is any, such water would be carried to great depths and undoubtedly becomes quite high in dissolved 14