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1.0 INTRODUCTION <br />The Flying W Pit will mine gravel below the natural water table. The operation will <br />utilize dry mining techniques and will trench the perimeter of the pit and pump <br />from the trenches to dewater the gravel within the pit area. These types of gravel <br />pits will create a cone of depression locally. This study utilizes the digital <br />program MODFLOW, which is a 3-dimensional finite difference numerical model <br />of groundwater flow. <br />MODFLOW is used as a predictive tool to approximate the potential influence the <br />cone of depression may have on the adjacent Thompson Ponds to the north of <br />the pits and Hillsborough Ditch to the South. <br />Reclamation proposes to line the mined out east pit with low permeability <br />compacted clay for the purpose of keeping groundwater from exposure to the <br />atmosphere. MODFLOW is used to predict local water table and pond water <br />elevations following placement of the low permeability compacted clay liner. <br />Strategies are presented to mitigate the effects of the dewatering operation <br />during pit operation and the potential effects of the low permeability liner <br />following reclamation. <br />MODFLOW is also used as a predictive tool to approximate the potential <br />influence the reclamation land configuration may have on the local water table. <br />Formatted MODFLOW input and output files are included in the Appendix. <br />Flying W Pit <br />Groundwater Modeling Report Revised June 28, 2005 <br />1 of 13 <br />