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1 - <br /> The major regional bedrock aquifers in the general area of the mines are <br /> the Cozette sandstone, Rollins sandstone, the Middle sandstone, and the <br /> Upper sandstone members of the Hesaverde Group; and the 'Wasatch <br /> Formation-Ohio Creek Conglomerate. <br /> The regional sandstone aquifers of the Hesaverde Group are thick, fine to <br /> medium-grained, calcium carbonate cemented, quartzitic sandstones. As <br /> Aquifers, they have low to moderate permeabilities and transmissivities. <br /> At the North Thompson Creek Mines, the only regional sandstone to have <br /> aquifer tests performed on it was the Upper sandstone memoer, which <br /> yielded a transmissivity value of 1700 gpd/ft. This value may be high <br /> due to fracture permeability. The Rollins, Cozette, and Middle <br /> sandstones, where fractured, should have similar transmissivities. The <br /> .eater quality analyses of the Upper sandstone member yield values for pH <br /> of 7.5 to 8.0, and TUS of 1262 mg/l . <br /> No wells are drawing water from the sandstones of the i'lesaverde Group in <br /> the general area. However, ground water mine inflows from the 'Williams <br /> Fork Formation are utilized by the mines. This water is used within the <br /> North Thompson Creek Mines, and used outside of the mine for a sanitary <br /> supply, for dust suppression, for equipment washdown and in the <br /> 1 washplant. This mine inflow water is tributary to both North and Middle <br /> Thompson Creeks. A small percentage of the inflow waters within the <br /> Sunlight and Coal Basin mines are used within the mines. The majority of <br /> l the mine 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 <br /> water. Ground water movement within the brittle coals is dependent on <br /> secondary porosity and is localized in fracture and fault zones. The <br /> highest occurrence of ground water in the coal seams is found in areas <br /> adjacent to and/or under streams. This occurrence is due to the <br /> combination of a good source of recharge water and a well developed <br /> fracture system associated with stream valleys in the area. <br /> The main streams and tributaries to Fourmile Creek, North Thompson Creek <br /> Miadle Thompson Creek, and Coal Creek cut across the Iles Formation and <br /> the coal -bearing strata of the 'Williams Fork Formation at right angles to <br /> strike. This suggests that the resistant Upper, Middle and Rollins <br /> sandstone members have been breached by the streams along fracture or <br /> vault zones. The existence of fracture controlled stream valleys is Q �' <br /> supported by ini ne inflow data. The occurrence of inflows into the three <br /> ;nines are greatest adjacent to and under stream valleys. The inflow t4 <br /> rates also mimic the flow characteristics of the adjacent strum. ti <br /> Perennial inflows are associated with perennial streams, and eohemeral �JY <br /> inflows are associated ,vita egheateral drainages. The increased inflows <br /> associated with the stream system are a function of the higher vertical t" <br /> permeability of the strata resulting from secondary fracture porosity in <br /> the stream valleys. The quantities of mine inflows and of the associated <br /> stream depletion are functions of 1 ) the area. of mine 'wor''Kings idjacent <br /> t0 -ne streams, 2) tree tnickness. of strata overlying the mine, 3) of the <br /> 1itnclogy of the overly ng and inderlVina strata, 1) of the stream f lo'w <br /> --naraCteristics, and J} the mining methods in the area :f the strearns. <br />