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Estimations of surface water runoff based onpre-mining and post- mining conditions aze included on <br />page 2.04.7-89 of the PAP. It is estimated that surface runoff from the permit area will decrease by <br />36 acre-feet per yeaz due to increased infiltration and evapotranspiration. This is approximately two <br />percent of the estimated annual flow of Goodspring and Taylor Creeks downstream from the permit <br />area. During its adequacy review of Permit Revision No. 1, the Division raised several questions <br />about the modeling assumptions used for generating these numbers and sizing surface water control <br />structures. The Operator re-evaluated the modeling procedures. All structures built before August 31, <br />1992 adequately detain and treat all waters originating from azeas disturbed through December 31, <br />1992. Structures built after August 31, 1992 detain and treat all waters originating from all remaining <br />areas disturbed. The Division finds no significant impacts to surface water quantity due to Colowyo's <br />mining operations. <br />Mined azeas will be reclaimed to approximate original contour with the exception of five excess <br />spoil fills. The sizes of drainage azeas 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 4,345 acres of disturbance during the life <br />of mine. As of the fall of 1991, approximately 503 acres of disturbed land in the East Pit and Section <br />11 Pit had been reclaimed. As of the end of 1996, a total of approximately 1,066 acres of disturbed <br />lands had been backfilled and graded, and 1,052 acres seeded. As of 2001, 1,376 acres of disturbed <br />lands had been backfilled, graded and seeded. As of 2006, 1,712.41 acres have been backfilled and <br />graded and 1,581.72 acres have been topsoiled and reseeded (2006 ARR}. <br />Runoff in the permit area, which is diverted or detained, will continue to reach the historic drainages. <br />A portion of the water rights held by Colowyo on Goodspring Creek may be consumed in accordance <br />with the augmentation plan discussed in Exhibit 7 of the Permit. <br />The increased infiltration of surface waters is not expected to recharge the ground water system. The <br />Applicant indicates that the increased soil water resulting from increased infiltration rates and <br />increased moisture-holding capacity will be consumed by increased evapotranspiration. The net <br />result is that water is rarely, if ever, given the opportunity to percolate into subsurface material. <br />The anticipated hydrologic consequences to surface water quantity for the South Taylor azea are; <br />• Natural springs neaz the South Taylor Pit might experience increased or decreased flow <br />• The South Taylor pit will eliminate several springs and seeps. <br />• Hydraulic transmissivity within the backfilled pit will be higher that the adjacent mined <br />azea <br />• Base flow in Good Spring Creek will be reduced by up to 7% during and for 45 years <br />after mining <br />• Peak flow in Taylor Creek will be reduced by 2% due to the South Taylor pit <br />Colowyo holds significant water rights on Goodspring Creek should surface water quantity issues <br />develop as a result of mining. Exhibit 7 of the approved permit discusses the augmentation plan for <br />Proposed Decision and Findings of Compliance 4 May 2007 <br />Permi[ Revision 02 Page 37 <br />