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No surface water will be discharged into underground mine workings. K. Stream Buffer Zones - Rule 4.05.18 The Division approved surface or underground mining activities within 100 feet or through a perennial stream or stream with a biological community. This decision was based on a finding that the original stream channel will be restored, water quality and quantity shall not be adversely affected, and appropriate riparian vegetation will be reestablished. The buffer zone variance is granted for portions of Goodspring Creek near the sediment ponds which discharge into that creek (Streeter Pond, Gulch A Pond and Prospect Pond), and that portion of Taylor Creek near the loadout [4.05.18(1)]. L. Probable Hydrologic Consequences A discussion of the probable hydrologic consequences of mining and reclamation operations is contained in pages 2.04.7-85 through 101 of the PAP. The original findings document (1982), an Amended Findings Document for Permit Renewal (1987), and Technical Revision No. 14 (1989) also include discussions of probable hydrologic consequences. Section 2.04.7 of the PAP and Section VI of the 1982 Findings Document contain extensive discussion of the hydrologic balance of the permit area. Probable Hydrologic Consequences for the South Taylor area are included in Section 2.05.6(3)(b)(iii) of Volume 12 1. Potential Effects on Surface Water Quantity Based on the hydrologic balance calculations for the drainages in the general area and the fact that all runoff from the mine area is to be either diverted around the mine or retained in sedimentation ponds for a maximum of 36 hours (Division of Water Resources), no change in the hydrologic balance will occur. Since the area to be mined is a fraction of the total watershed areas, the general area will not be affected. The probable hydrologic consequences (PHC) section of the 1982 Findings Document predicted that there would be no significant effects to the hydrologic balance of Taylor, Wilson or Goodspring Creeks as a result of mining. Monitoring data in the mine's Annual Reclamation Reports (ARR's) to date confirms that there have been no significant impacts on water quantity of these streams to date due to mining operations at the Colowyo Mine. Estimations of surface water runoff based on pre-mining and post- mining conditions are included on page 2.04.7-89 of the PAP. It is estimated that surface runoff from the permit area will decrease by 36 acre-feet per year due to increased infiltration and evapotranspiration. This is approximately two percent of the estimated annual flow of Goodspring and Taylor Creeks downstream from the permit area. During its adequacy review of Permit Revision No. 1, the Division raised several questions about the modeling assumptions used for generating these numbers and sizing surface water control structures. The Operator has re-evaluated the hydrologic modeling procedures. All structures built before August 31, 1992 adequately detain Proposed Decision and Findings of Compliance 14 September 2009 Permit Renewal 05 Page 39