2013-04-10_GENERAL DOCUMENTS - C1981019

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change in the hydrologic balance is likely to occur. Furthermore, the area to be mined is a small fraction of watershed areas, and the general area will not be greatly affected. A discussion of the probable hydrologic consequences is found in Volume 15, Rule 4. 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 re- evaluated the modeling procedures. All structures built before August 31, 1992 adequately detain and treat all waters originating from areas disturbed through December 31, 1992. Structures built after August 31, 1992 detain and treat all waters originating from all remaining areas disturbed. The Division finds no significant impacts to surface water quantity due to Colowyo's mining operations. Mined areas will be reclaimed to approximate original contour with the exception of five excess spoil fills. Approximately 4,800.0 (2011 Annual Reclamation Report (ARR)) of the approximately 5,018 acres permitted for disturbance have been disturbed. Of the disturbed, approximately 2,210.54 acres have been backfilled and graded, and of this approximately 2,088.65 acres have been topsoiled and seeded (2011 ARR). Phase I bond release for approximately 226 acres and Phase II bond release for approximately 176 acres for portions of Streeter Fill were applied for and granted in 1987 (PAP). A Phase I bond release for approximately 712 acres was granted in 1998 (Findings, 1997 Phase I Partial Bond Release Application). A Phase II bond release (SL -3) for approximately 762 acres was granted in August 15, 2001 (Findings, 2000 Application for Partial Phase 11 Bond Release). On May 2, 2011, SL -4 approved 494.2 acres Phase I bond release and 420.9 acres for Phase II bond release. On July 25, 2012, the Division approved Phase III bond release (SL -5) for 979.52 acres of reclaimed area in the East Pit, Section 16 Pit and a portion of the West Pit Fill. SL -6 is currently under review Colowyo Coal Mine C1981 -019 PR -03 46 April 10, 2013