2004-10-20_GENERAL DOCUMENTS - C1981018

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E. Probable Hydrologic Consequences The probable hydrologic consequences of mining within the Deserado Permit Area are addressed within Section II.C.S of the permit application. The permittee's statement of hydrologic effects has been reviewed by the Division for compliance with Rule 4.05.1 and 2.05.6(3). Impact of the Mining Operation on Surface Water Impacts to the hydrologic balance will occur as a result of the mine. Short-term impacts which will occur as a result of surface facilities appurtenant to the under- ground mine include reduction of water yield from the mine azea to the White River, increased sediment loads from disturbed azeas, and water quality degradation from the refuse disposal azea and mine water dischazge. Long-term impacts will center on the effects of subsidence under Scullion Gulch and Red Wash. See the subsidence section of this document for further discussion of subsidence impacts. Small, short-term surface water losses will occur as a result of two factors, retention of water in ponds and removal of water from the White River Lagoon. Runoff from disturbed azeas will be routed through sedimentation ponds, thereby reducing the amount of flow to the White River. Evaporation losses will occur because the ponds will not discharge runoff until some of the available storage volume is filled. Very little of the impounded water will re-enter the ground water system due to the clay subsoils which comprise the pond bottoms. Losses from the D-Portal pond will be insignificant when compazed to total runoff from the Scullion Gulch watershed. The pond is designed to store runoff from 44 acres, while Scullion Gulch has a contributing drainage area of 7,552 acres at its confluence with the White River. The refuse disposal azea ponds receive runoff from approximately 98 acres, which is a very small portion of the 2,950 acres drained by the Red Wash tributary through the northern sector of the permit azea. $ased on this information, the net loss of surface water quantity to Red Wash and the White River will be negligible. Water supply for the mine will come from the White River Lagoon. Combined water use and evaporative loss at full production is projected to consume 552 acre-feet per yeaz at a withdrawal rate of .763 cubic feet per second. This translates to less than 0.2 percent of the average annual flow in the river of 672 cfs. Even during low flow conditions, when the average flow is 245 cfs, the withdrawal rate will only be 0.31 percent of the available flow. Therefore, adverse impacts on flow in the White River as a result of proposed withdrawal should be minimal. Furthermore, the permittee has secured water rights downstream of the mine that may be used if necessary to replace a depleted water - - - source. -- - - - - --- - - - 30