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<br />Groundwater Impact <br />' The proposed mining 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 draglinelbackhoe. 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 <br />incurred during nesting would be augmented by the operator in an approved substitute water <br />' supply plan. There will be no impacts on the groundwater table on the east side of the river. <br />The operator proposes to install a slurry wall around the perimeter of the property west of <br />the S. Platte River prior to beginning dewatering operations. The slurry wall will prevent any <br />draw down on the groundwater table outside of the property. Quantification of the "laterial <br />and vertical" extent of the mounding or shadow effect will vary depending on time of year, <br />' and return flow patterns established in the area. The vertical mounding of groundwater <br />against a slurry wall could range from 1 to 5 feet. The current depth to groundwater in the <br />proposed mining area ranges from between 5 to 7 feet which indicates a very shallow <br />' groundwater table. Proposed monitoring wells will give better field data to determine what <br />impacts will be, but the mounding affect of the slurry wall is not expected to cause any <br />flooding of basements. The "lateral" extent of mounding would be function of seasonal <br />' conditions. Generally, return flows, precipitation and recharge from sources such as ditch <br />seepage, tailwater, etc. would be expected to extend between 500 to 1,000 feet beyond the <br />slurry wall. This means that the elevated groundwater levels in the aquifer would be <br />' dissipated within this distance. The shadow affects of the slurry wall for this particular <br />location are expected to be minor. The area would be on the north side of the mining area <br />on the west side of the river. Most of the adjacent property downstream of the site is unlined <br />mined gravel pits and would not be adversely impacted. These pits are adjacent to the river, <br />which would supply some recharge to the area. There may be a reduction in the groundwater <br />table of 1 to 3 feet during some times of the year, but this would not be expected to adversely <br />' impact any wells in the area. <br /> <br />1 <br /> <br /> <br />11 <br />