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along the east wall of the pit. The drain conductance value is the same as the <br />drain modeled above - 30,000 sq ft/day. <br />1.5. MODEL CALIBRATION <br />The model was calibrated to within 10% of measured heads in the area of the <br />proposed pit (see Sheet 1). The calibration was performed by varying the <br />constant head boundaries until the water levels from the model output matched <br />the measured head to within 10%. <br />1.6. MODEL OUTPUT <br />Model output was contoured and is shown in Sheets 2-4. Sheet 1 shows existing <br />water levels. Proposed pumping water table elevations were subtracted from <br />existing water levels to show relative drawdown due to pumping conditions <br />(Sheet 3). Sheet 4 shows.the water table after reclamation. <br />1.6.1. Existing Water Level Conditions <br />The first model run was developed to simulate existing water elevations. The <br />model output for the existing Water Level simulation following calibration is <br />shown in Sheet-2. The model output of cell by cell flow budgets under existing <br />conditions showed a ditch loss of 24,000 cu ft/day (125 gpm) for the length of the <br />canal in the model, approximately one mile. The canal seepage drain was <br />inflowing 29,753 cu ft/day (155 gpm) <br />1.6.2. Pumping Conditions 1,970 gym <br />The pumping simulation was performed setting the total pumping flow rate at <br />1,970 gpm. At the toe of the pit wall, the water table was drawn down to <br />approximately 3-4 ft above the pit bottom, which is consistent with observations <br />of seepage faces for other similar gravel pits in the area. The simulated pumping <br />water table elevations were subtracted from the simulated existing water table <br />elevations to yield drawdown. The drawdown contours for pumping conditions <br />are shown on Sheet-2. <br />During pumping conditions the canal seepage drain picked up slightly less water, <br />29,356 cu ftiday (153 gpm), than it did under the existing model conditions. The <br />canal seepage remained the same in both cases at 125 gpm. <br />1.6.3. Reclamation <br />The reclamation model output water table elevation contours are shown on <br />Sheet-4. Comparison of Sheet-4 to Sheet-2 shows that mounding is not <br />occurring on the upstream face of the former pit (east wall). The model did show <br />that mounding would happen without the perimeter drain. The addition of the <br />perimeter drain to the model removed the mound. The MODFLOW output budget <br />for the perimeter drain calculates a total flow of 450 gpm (90,300 cu ft/day). <br />File Pit 112 <br />Groundwater Modeling Report <br />4 of 6 <br />