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<br />The project lies in the valley fill deposit for the Brighton Reach of the S. Platte River. This <br />is an alluvial aquifer that is unconfined and consists of the sand and gravel that is being mined. <br />The limits of the aquifer correspond roughly to the limits of the floodplain. The depth of the <br />aquifer ranges from approximately ]0' to 50' depending upon the conformation of the <br />underlying bedrock. It is estimated that bedrock lies between 25' to 35' below the proposed <br />mining site. <br />The underlying bedrock is the Denver formation, which is a blue claystone-siltstone formation <br />that is several hundred feet thick. This formation is almost totally impermeable. There are <br />no known intrusions into the formation on this property. The upper three feet is weathered <br />and has some minor fracturing. The unweathered shale is competent as a seepage barrier. The <br />claystone in a decomposed form is an excellent impermeable zone material in the construction <br />of reservoir liners or dams. The consistency of bedrock will be monitored during the mining <br />operation to determine if there are any geologic anomalies that create seepage paths into the <br />proposed reservoir. <br />There are several non-tributary aquifers that underlie the Denver formation. These include <br />the Upper and Lower Arapahoe and the Laramie Fox-Hills. These aquifers are confined in <br />this area and will not be affected by the proposed mining operation. <br />Groundwater Impacts <br />A9~-ob <br />o5E <br />~7 <br />~~ <br />The proposed nuning and reclamation plan will require wet mining the aquifer on the east side <br />of the S. Platte River (See Exhibit C-2, Mining Plan Map). Approximately 30 acres that is <br />bounded by the S. Platte River on the west and the Fulton Ditch on the east will be mined in <br />an unlined condition using a dragline/backhoe. The exposed groundwater lake will exist over <br />the life of the mine. This area will serve as a silt pond for the processing operation as mining <br />progresses to the west side of the river. This silt pond will be gradually filled in by silts and (- <br />clays washed from the mined material. The only impact that would occur on the east side of <br />the river would be from evaporative losses from the exposed lake surface. Once mining and <br />reclamation is completed, there will be no exposed lakes left. The consumptive water losses ~~sPe~° <br />incurred during mining would be augmented by the operator in an approved substitute water <br />supply plan. ~ 9c~ <br />There will be no impacts on the groundwater table on the e ~t side of the river. The operator ~(T <br />proposes to install a slurry wall around the perimeter of the property prior to beginning <br />dewatering operations. The slurry wall will prevent any draw down on the groundwater table <br />outside of the property. The slurry wall may create some mounding of groundwater on the <br />upgradient side. Mounding will not adversely impact groundwater we_lls/.~_ <br />J ' <br />