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-31- <br /> The colluvial deposits formed of talus and unconsolidated landslide deposits <br /> support spring and seep flows in the Coal Basin Drainage. During spring <br /> snowmelt, these deposits recharge. The ground water migrates to the toe of <br /> the slides and discharges as intermittent and perennial springs and seeps. <br /> The major regional bedrock aquifers in the general area of the mines are the <br /> Cozette sandstone, Rollins sandstone, the Middle sandstone, and the Upper <br /> sandstone members of the Mesaverde Group; and the Wasatch Formation-Ohio Creek <br /> Conglomerate. <br /> The regional sandstone aquifers of the Mesaverde Group are thick, fine to <br /> medium-grained, calcium carbonate cemented, quartzitic sandstones. As <br /> aquifers, they have low to moderate permeabilities and transmissivities. At <br /> the North Thompson Creek Mines, the only regional sandstone to have aquifer <br /> tests performed on it was the Upper sandstone member, which yielded a <br /> transmissivity value of 1700 gpd/ft. This value may be high due to fracture <br /> permeability. The Rollins, Cozette, and Middle sandstones, where fractured, <br /> should have similar transmissivities. The water quality analyses of the Upper <br /> sandstone member yield values for pH of 7.5 to 8.0, and TDS of 1262 mg/l . <br /> No wells are drawing water from the sandstones of the Mesaverde Group in the <br /> general area. However, a portion of the ground water mine inflows from the <br /> Williams Fork Formation are utilized by the mines. This water is used within <br /> the North Thompson Creek Mines, and used outside of the mine for a sanitary <br /> supply, for dust suppression, for equipment washdown and in the washplant. A <br /> portion of this mine inflow water may be tributary to both North and Middle <br /> Thompson Creeks. A small percentage of the inflow waters within the Sunlight <br /> and Coal Basin mines are used within the mines. The majority of the mine <br /> waters from these two mines are discharged to the surface. <br /> The coal seams of the Williams Fork Formation are not aquifers, since the <br /> coals are tight and have insufficient primary porosity to transmit water. <br /> Ground water movement within the brittle coals is dependent on secondary <br /> porosity and is localized in fracture and fault zones. The highest occurrence <br /> of ground water in the coal seams is found in areas adjacent to and/or under <br /> streams. This occurrence is due to the combination of a good source of <br /> recharge water and a well developed fracture system associated with stream <br /> valleys in the area. <br /> The main streams and tributaries to Fourmile Creek, North Thompson Creek, <br /> Middle Thompson Creek, and Coal Creek cut across the Iles Formation and the <br /> coal-bearing strata of the Williams Fork Formation at right angles to strike. <br /> This suggests that the resistant Upper, Middle and Rollins sandstone members <br /> have been breached by the streams along fracture or fault zones. The <br /> existence of fracture controlled stream valleys is supported by mine inflow <br /> data. The occurrence of inflows into the three mines are greatest adjacent to <br /> and under stream valleys. The inflow rates also mimic the flow <br />