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2.4.4. West Pit Reclamation <br />The reclamation plan is to backfill the eastern 1/3'dof the pit excavation as shown <br />in Sheet 3. The western 2/3~d will be left as a groundwater fed pond with a <br />surface area of approximately 3.7 acres. The pond was left unlined for the <br />purpose of preventing water table mounding that could result from placement of a <br />low permeability clay liner. The pond is predicted to have an overall lowering of <br />the water table due to the fact that the open pond water surface will act as an <br />evaporative pump to the atmosphere. The model uses a net evaporation rate of <br />2.3 acre-feet per acre of pond. <br />2.4.5. East Pit Dewaterinq <br />The perimeter drains around the East Pit are set at 1.5 feet above the base of the <br />pit and yielded a total of about 850 gpm. <br />2.4.6. East Pit Reclamation <br />The east pit excavation will become a pond with a clay liner to disconnect it from <br />the natural ground water table and the river. The clay liner in the model has a <br />hydraulic conductivity of 0.003 ft/day as is required by the State Engineer. <br />2.5. Dewaterinq Yield Discharge <br />The water produced during mining will be conveyed to the mined out pit east of <br />the permit boundary. This pit is has been sealed off from the gravel aquifer with a <br />clay liner. The water pumped to the pit will be allowed to evaporate. <br />2.6. Model Boundary Conditions <br />The principle boundary conditions were prescribed heads at perimeter cells of <br />the model domain, surveyed surface water elevations (measured on April 11, <br />2003) of the river at river cells and_ inactive model cells south of the river. <br />Because the river is a constant head boundary, the model cells south of the river <br />were turned off to simplify computation time. The inactive area of cells east of the <br />east pit is a previously mined out gravel pit. This reclaimed area is clay lined and <br />is a normally dry depression not connected to the alluvial aquifer. <br />Gardels Pit <br />Revised Groundwater Modeling Report <br />4of9 <br />