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• approximately 200 feet per year, the plume could be expected to reach the GC-2 monitoring well <br />approximately 10 years after backfilling and resaturation of the spoil aquifer in A East pit is complete. <br />Elevated TDS levels could extend to monitoring well GP-9 roughly 40 years after resaturation occurs. The <br />Big Bottom syncline lies north of the Trapper project area in the Flume Gulch drainage and will limit the <br />extent of the migration to the north. The plume can be projected to move generalty northward with the <br />structural orientation of the Third White Sandstone acting to change the prevailing direction of <br />groundwater flow to the northwest as one moves further from the mined area. Ultimately, waters in the <br />Third White Sandstone emanating from the mined area will flow in a westerly direction along fhe axis of <br />the Big Bottom syncline. No currently existing adjudicated wells are expected to be impacted by the <br />potential development and migration of this plume. Water quality in the Third White Sandstone will not be <br />degraded to the point it is no longer suitable for current uses. <br />4.8.3.3 Post Mine Hvdrolooic Balance <br />Precipitation amounts are expected to be similar to pre-mine conditions after mining. Section 2.7.6.1 <br />discusses pre-mine precipitation. Evapotranspiration is likely to be less during the first few years after <br />mining because the decrease in vegetative cover should decrease transpiration. Evapotranspiration <br />should approach the pre-mine values as vegetation is re-established. <br />• <br />If recharge to the spoils is larger than pre-mine values, direct surface runoff will be reduced subsequent to <br />mining. A larger net groundwater discharge to the surface system is likely in areas where spoil springs <br />develop. These discharges could offset a decrease in direct surface runoff from the reclaimed surfaces. <br />The larger amount of groundwater discharge to springs will increase the water availability for wildlife and <br />livestock in the area for a greater portion of the year. <br />4.8.4 Impacts to Potential Alluvial Valley Systems <br />Little potential exists for impact to the Williams Fork alluvial system because very little surface water and <br />essentially no groundwater from the proposed mine plan area flow toward the Williams Fork River. <br />Section 2.7.7.1 should be consulted for details. The potential for impact to the Yampa alluvial system is <br />very small because the Upper Williams Fork aquifers yield only a very small percentage of the water in <br />this system. Additional information on the Yampa River alluvial system is given in Section 2.7.7.2. <br />Potential alluvial valley floors in the drainages leaving the proposed mine plan area are addressed in <br />Section 2.7.7.3. <br />• The definition of the geologic conVol of groundwater movement at one of the potential AVF sites will typify <br />all of the sites. The Pyeatt aquifer system was selected for this purpose. Section 2.7.7.3 presents the <br />aquifer information on this site. The piezometric surfaces in Map M32 indicate that the shallow aquifer <br />system in Pyeatt obtains a significant amount of groundwater from the Second White Sandstone (SS <br />4-238h <br />[;°~~ion: Tit' 1P <br />~,.11~~o:-eBCT 2 <br />