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calculated by MODFLOW as negative drawdown. The steady state model for the reclaimed <br />conditions produced higher groundwater elevation heads than those produced for the pre-mining <br />steady state condition. The difference between these two groundwater surfaces are the predicted <br />mounding isopachs shown on Figure E-2. For the predictive simulation,positive residuals are <br />reported as values of groundwater mounding(warm colors) and negative values represent <br />groundwater shadowing(cool colors). The magnitude of the maximum groundwater mounding <br />is approximately 1.65 feet upgradient of the pit filled with wash fines. The residuals for the two <br />closest predictive simulation targets,wells 262268 &279124, are 0.33 and 0.72 feet, respectively <br />Figure E-2). These residuals represent depths to groundwater of about 6.5 feet. The results of <br />this simulation further indicate that the magnitude of the maximum groundwater shadowing is <br />1.5 feet downgradient of the proposed slurry wall. <br />Predicted Mitigated Groundwater Mounding with an Underdrain <br />The predictive model showing groundwater mounding for the reclaimed conditions was changed <br />by adding an underdrain between the property boundary and the proposed wash-fines depository. <br />The drain simulation was performed using a drain with an upstream invert elevation of 4526, and <br />an outfall elevation equal to 4523. The beginning elevation(4526)represents the mounded <br />groundwater head upgradient of the property for the unmitigated condition. The ending <br />elevation(4523)represents the estimated initial groundwater head prior to the reclamation <br />condition. The drain is approximately 1,100 feet long, and would discharge down-gradient of <br />the wash fines depository into a below-grade pit filled with gravel and cobbles. The simulated <br />drain was given the following parameters: <br />Beginning drain elevation=4526 <br />Ending drain elevation=4523 <br />Drain width,w= 1 foot (based on a 1-foot wide trench filled with a gravel bedding) <br />Drain length, L= 50 feet (width of model grid cell) <br />Drain bed thickness, dl= 1 foot <br />Hydraulic conductivity, K= 500 feet per day(same as aquifer K,which is assumed to be <br />smaller than gravel bedding K and therefore controlling) <br />Drain conductance=25,000 square feet per day, C=K*(dl/w)*L <br />The results of the simulation with the drain are presented on Figure E-3. This map is the same <br />as Figure E-2, except it shows the mitigated groundwater mounding and the location of the <br />proposed drain as a boundary condition. The mitigated groundwater mounding upgradient of the <br />property is less than one foot, an improvement of more than half a foot in the most critical area. <br />The drained mound is limited by the downgradient elevation of the drain, which roughly <br />reestablishes the pre-reclamation groundwater condition. The mass balance for the simulation is <br />approximately-0.002 percent. Groundwater flow to the drain is approximately 1,440 cubic feet <br />per day(cfd), which is about 7.5 gallons per minute (gpm) or 0.17 cubic feet per second(cfs). <br />The residuals for the two closest predictive simulation targets, wells 262268 &279124, are 0.29 <br />and 0.63 feet,respectively. Although these values are similar to those for the unmitigated <br />condition, they are lower. Because the extent of the highest part of the mound for the <br />unmitigated condition does not include these wells, we propose installing a new well on the <br />property within the predicted unmitigated high mound as shown on Figure E-4. This well will <br />be monitored closely following reclamation activities. If the depth to groundwater in this well <br />E-6