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that all runoff from the mine area is to be either diverted around the mine or retained in <br />sedimentation ponds for a maximum of 36 hours (Division of Water Resources), no change in the <br />hydrologic balance will occur. Since the area to be mined is a fraction of the total watershed <br />areas, the general area will not be affected. <br />The probable hydrologic consequences (PHC) section of the 1982 Findings Document predicted <br />that there would be no significant effects to the hydrologic balance of Taylor, Wilson or <br />Goodspring Creeks as a result of mining. Monitoring data in the mine's Annual Reclamation <br />Reports (ARR's) to date confirms that there have been no significant impacts on water quantity of <br />these streams to date due to mining operations at the Colowyo Mine. <br />Estimations of surface water runoff based on pre-mining and post- mining conditions are <br />included on page 2.04.7-89 of the Permit. It is estimated that surface runoff from the permit area <br />will decrease by 36 acre-feet per year due to increased infiltration and evapotranspiration. This is <br />approximately two percent of the estimated annual flow of Goodspring and Taylor Creeks <br />downstream from the permit azea. During its adequacy review of Permit Revision No. 1, the <br />Division raised several questions about the modeling assumptions used for generating these <br />numbers and sizing surface water control structures. The operator re-evaluated the modeling <br />procedures. All structures built before August 31, 1992 adequately detain and treat all waters <br />originating from areas disturbed through December 31, 1992. Structures built afrer August 31, <br />1992 detain and treat all waters originating from all remaining areas disturbed. The Division <br />finds no significant impacts to surface water quantity due to Colowyo's mining operations. <br />Mined areas will be reclaimed to approximate original contour with the exception of three excess <br />spoil fills. The sizes of drainage areas for some ephemeral and intermittent drainages within the <br />mined azea will be changed; however, there will be no changes to drainage sizes for Goodspring, <br />Taylor or Wilson Creeks. The proposed mine plan projects 3,810 acres of disturbance during the <br />life of mine. As of the fall of 1991, approximately 503 acres of disturbed land in the East Pit and <br />Section 11 Pit had been reclaimed. As of the end of 1996, a total of approximately 1,066 acres of <br />39 Revised October 30, 1997 <br />