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<br />CHAPTER 5 -CHANGES TO ALLUVIAL AQUIFER -STREAM SYSTEM <br />' RELATIONSHIP <br />5,1 Introduction <br />' As previously discussed, the elimination of the mined portion of the alluvial aquifer at the Lyons - <br />Rockin' WP Pit has the potential to alter the hydrologic storage function of the aquifer. Changes in <br />' the aquifer storage capabilities, resulting in changes to the recharge and discharge pro~~esses could <br />result in changes in streamflows. In order to analyze the potential impacts of mining on this process, <br />' a water budget spreadsheet was developed which compares the flow between the alluvial aquifer and <br />the streams prior to mining conditions to the flow between the alluvial aquifer and the :streams after <br />' mining is completed. <br />' To develop the water budget spreadsheet, water level data collected from a series of piezometers <br />installed within the mining permit azea were evaluated. Based upon the water level fluctuations, the <br />' seasonal changes in historic aquifer storage, including volumes of flow from the stream to the aquifer <br />during recharge and from the aquifer to the stream during discharge, were determined. Likewise, <br />' the seasonal changes in the future aquifer storage function were determined. Historic conditions <br />were compazed to future conditions to determine if significant impacts on the aquifer-stream system <br />relationship, and corresponding changes in streamflow, can be expected to occur. The analysis took <br />' into account impacts not only from the amended permit application, but from ttie previously <br />permitted mining as well. <br />' The analysis presented herein does not evaluate impacts to the stream from water con:;umed as part <br />' of the mining process or from evaporative losses from exposed ground water at the pit. These losses <br />will need to be replaced under Colorado law and therefore, will cause no ne~v impacts to the stream <br />' system. For the existing permitted areas, the impact to the stream from evaporative losses is already <br />offset by historic consumptive use credits from irrigation water rights dedicated ':o an existing <br />' Augmentation Agreement. For the areas under the amended permit, all future water losses will be <br />' -22- <br />' 1 /fi~bn/~ lrnmil,,, .~~ro,i~u~,. ln,. <br />