2009-05-12_REVISION - C1981025 (8)

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disturbance are at Portal 1 and Portal 1 facilities areas, the underground workings beneath North Thompson Creek, and the conveyor over the Roaring Fork River. The coal mine waste pile and pond, and four water-monitoring flumes were permitted. [Rule 4.05.18(1)] F. Probable Hydrologic Consequences of the North Thompson Creek Mines There is no known underground mine water discharge from North Thompson Creek Mines in the Middle Thompson Creek drainage. There are no known impacts to groundwater in the Middle Thompson Creek drainage from mining and reclamation activities or to the Roaring Fork River from the loadout site. 1. Ground Water Current discharges indicate that both the North Thompson Creek No. 1 and No. 3 Mines are experiencing mine inflows. The mine portal discharges represent a redirection in the migration of groundwater from pre-mining conditions. Inflow maps, descriptions of inflows, and water quality analyses of inflows applicable to periods of mining are within the PAP. The inflow water quality analyses indicate that there may be at least two sources of water. The inflows with low total dissolved solids (TDS) concentrations have water qualities similar to surface waters. This suggests that these inflows may be transmitted directly to the mine workings from the surface water system, with very little residence time in the transmitting aquifer, or are emanating from aquifers with few dissolvable solids. These low TDS inflows are also generally found emanating from fractures beneath or directly adjacent to the stream valleys of North and Middle Thompson Creeks. High TDS inflows are thought to indicate longer residence time and reactive time with soluble minerals in the transmitting aquifer. These inflows may thus 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 long-wall 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 North Thompson Creek C-1981-025 Permit Renewal 05 12 May 2009 17