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<br />Mining effects were divided into short-term effects and long-term effects. <br />These time frames are relative. Short-term effects include surface and ground <br />water effects that would occur during the mining operation and for a short <br />time following operations, such as discharge from sediment ponds, discharge <br />from underground mine workings, and the discharge of affected waters from <br />shallow ground water systems. <br />The natural flow patterns of the affected ground water systems is disrupted <br />during mining, and surface and ground water is mixed. Increased evaporation <br />losses from the sediment ponds are assumed to be offset by increased runoff <br />from disturbed areas. <br />The long-term effects of mining occur after disturbed areas have been <br />successfully reclaimed. The surface and ground water systems have had <br />sufficient time to equilibrate, sediment control structures have been removed <br />and the quantity and quality of runoff from the reclaimed areas has returned <br />to pre-mining conditions, spoils aquifers and underground mine workings have <br />resaturated, and ground water passing through the disturbed area discharges to <br />its pre-mining discharge areas. The quantity of ground water flows would <br />equal pre-mining quantities, but its quality would be degraded. <br />The Dry Creek Drainage Basin lies below the output node for the U.S.G.S. <br />model, however, in anticipation of mining activities in the drainage, this <br />area was examined. The Seneca II-W Mine is the only anticipated mine within <br />the Dry Creek drainage. <br />The output node for the U. S. G.S. model lies at the U.S.G. S. gaging station on <br />the Yampa River near Hayden. The effects of Dry Creek at its mouth were added <br />directly to the output model node to determine cumulative effects on the <br />Yampa River. <br />For the model, limited data was available on Dry Creek from data collected at <br />the U.S.G.S. gaging station on Hubberson Gulch (09244464). Mining effects <br />were estimated both for the short-term and long-term. The model did not <br />estimate any change in post-mining surface water except as it is effected by <br />ground water discharging to the surface water system. <br />Stokes Gulch, a tributary to Dry Creek, only flows in March through June and <br />exhibits high dissolved solids. This tributary elevates TDS levels in <br />Dry Creek during a period when the Teveis would normally be diluted. <br />The results of the model are shown on Table 1. During mining, a slight <br />increase in TDS levels occurs on Dry Creek, but there is no increase evident <br />on the Yampa below the confl uence with Dry Creek. The long-term effects show <br />an increase in TDS levels above mining levels on Dry Creek, but again there <br />are negligible effects on the Yampa River. <br />A complete discussion of the effects of mining on Dry Creek below Seneca II-W <br />Mine is contained in the Probable Hydrologic Consequences section of this <br />document. Based upon the U. S. G.S. model run, it is expected that by the time <br />affected waters have reached the Yampa River, they will have been sufficiently <br />diluted to have a negligible effect on the river. Therefore, it was found <br />that the Seneca II-W Mine will not have any significant impacts on the Yampa <br />River. <br />- 39 - <br />