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impacts which will occur as a result of surface facilities appurtenant to the under- <br /> ground mine include reduction of water yield from the mine area to the White <br /> River, increased sediment loads from disturbed areas, and water quality <br /> degradation from the refuse disposal area and mine water discharge. Long-term <br /> impacts will center on the effects of subsidence under Scullion Gulch and Red <br /> Wash. See the subsidence section of this document for further discussion of <br /> subsidence impacts. <br /> Small, short-term surface water losses will occur as a result of two factors: <br /> retention of water in ponds and removal of water from the White River Lagoon. <br /> Runoff from disturbed areas will be routed through sedimentation ponds,thereby <br /> reducing the amount of flow to the White River. Evaporation losses will occur <br /> because the ponds will not discharge runoff until some of the available storage <br /> volume is filled. Very little of the impounded water will re-enter the ground <br /> water system due to the clay subsoils which comprise the pond bottoms. Losses <br /> from the D-Portal pond will be insignificant when compared to total runoff from <br /> the Scullion Gulch watershed. The pond is designed to store runoff from 44 <br /> acres,while Scullion Gulch has a contributing drainage area of 7,552 acres at its <br /> confluence with the White River. The refuse disposal area ponds receive runoff <br /> from approximately 98 acres,which is a very small portion of the 2,950 acres <br /> drained by the Red Wash tributary through the northern sector of the permit area. <br /> Based on this information, the net loss of surface water quantity to Red Wash and <br /> the White River will be negligible. <br /> Water supply for the mine is supplied by the White River. Combined water use <br /> and evaporative loss at full production is projected to consume 552 acre-feet per <br /> year at a withdrawal rate of.763 cubic feet per second. This translates to less <br /> than 0.2 percent of the average annual flow in the river of 672 cfs. Even during <br /> low flow conditions,when the average flow is 245 cfs,the withdrawal rate will <br /> only be 0.31 percent of the available flow. Therefore, adverse impacts on flow in <br /> the White River as a result of proposed withdrawal should be minimal. <br /> The construction of surface facilities in the permit area will cause temporary <br /> increases in the amount of suspended solids in the surface water system. <br /> Furthermore, concentration of chemicals associated with increased sediment <br /> load, such as iron and manganese,will also increase. At the Deserado Mine, <br /> mitigation of sediment load will be accomplished primarily by sedimentation <br /> ponds. Although sediment increases will occur in the early phases of <br /> construction,the long-term sediment yield may actually decrease below the <br /> already high natural occurrence of sediment concentrations due to the installation <br /> of control measures. <br /> Effects on the surface water system from the refuse disposal area should be <br /> minimal. Analysis of the waste material does not indicate the presence of toxic <br /> or acid-forming characteristics. The waste will be covered with 30 inches of non- <br /> toxic,non-combustible material,thereby reducing the potential for water quality <br /> xxviii <br />