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<br />_19_ <br />2) The proposed mining operations would not cause material damage to <br />the quantity and quality of the surface and ground water that supply the <br />alluvial valley floor, Discharge of mine water at a maximum rate of 65C <br />gpm from the underground mine workings would affect the quantity and <br />quality of flows in both the surface water and alluvial ground water <br />systems of these alluvial valley floors. (Any increase in quantity of <br />flows would be a beneficial effect, and need not be considered further.) <br />Along lower Foidel Creek, a baseflow may develop solely from the <br />discharge from the mine. Part of this flow would infiltrate the <br />streambed to enter the alluvial ground water system where it would be <br />diluted by existing flow in the alluvium. The affected concentration of <br />total dissolved solids in the surface and ground water systems are <br />expected to be S00 mg/1 or less. These concentrations would not have an <br />adverst effect upon most crops ( EPA, 1976, p. 208). <br />Downstream, the water quality effects would be further diluted by flows <br />in the Middle Creek and the Trout Creek stream/alluvial aquifer systems. <br />The applicant has calculated that the operation would increase the TDS <br />concentrations in surface flows below the confluence with Trout Creek and <br />would be approximately 145 mg/1. Added to the existing low flow <br />concentrations, this would provide an affected concentration below 500 <br />mg/1. Water of this quality would have no detrimental effect if used for <br />flood irrigation (EPA, 1976). <br />3) The proposed operations would preserve, throughout the mining <br />operation, the essential hydrologic functions of the alluvial valley <br />floor. The essential hydrologic functions for these alluvial valley <br />floors have been identified as the capacity to support both flood <br />irrigated and subirrigated agricultural activities. Since no mining <br />activities would occur within or beneath the alluvial valley floor, and <br />since no material damage would occur to the surface and ground water that <br />supply the alluvial valley floor, the essential hydrologic functions of <br />the alluvial valley floor would not be affected by the proposed <br />operations. <br />VIII. <br />This Cumulative Hydrologic Impact Study (CRIB) for a portion of the Yampa <br />River basin has been prepared by the Colorado Mined Land Reclamation <br />Division (CMLRD) pursuant to Rule 2.07.6(2)(c), This CHIS assesses the <br />projected cumulative hydrologic impacts of all anticipated mining <br />operations in the general area of the proposed Foidel Creek underground <br />mine. As discussed below, the surface water and ground water general <br />areas do not coincide (Figure 1). The ground water general area is <br />smaller because of structural limitations. Anticipated mining is defined <br />as the existing mines and those for which complete permit applications, <br />have been submitted to the Division. Coal mining operations in the study <br />area (Figure 2) include: <br />