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are relative to each other. Due to the higher conductivity in the spoil, the velocity vectors <br />in the spoil are significantly larger than those in the overburden. Although there are no <br />pumping wells or drains in this model, the drawdown model showed drawdowns of up to <br />40 feet, particularly in the vicinity of cells with a constant head value assigned to them. <br />The second model used all of the input parameters from the first model, but a line of <br />drain cells were added across the area within the permit boundary. The drain simulates <br />an open pit during mining. The bottom drain elevation for each cell is the approximate <br />floor of the pit at that location. Room was left on either side of the drain to simulate the <br />barrier pillars between the pit and the permit boundary. All cells south of the drain were <br />deactivated. No spoil was assumed in this model. When the model was run (see Figure <br />2.05.6(3) -2e), the equipotential surface generally mirrored that of the first model, <br />however close to the drain it sees a noticeable drop in elevation. The drop is greater on <br />the west side of the drain. The differences in head values on the west side of the pit are <br />highly similar to the drawdown seen in monitoring location GW -N8 as the highwall <br />approached (see Figure 2.05.6(3) -2a for the hydrograph). Velocity vectors in the region <br />of the highwall change directions towards the pit as they flow into the drain. The <br />drawdown model indicated values as high as 60 feet close to the drain. Since such a <br />drawdown would put the equipotential surface of the overburden below the coal zone, <br />such a value is not possible and the drawdown model was disregarded. This anomaly <br />was most likely caused by the drawdowns produced near constant head cells as seen in <br />the first model (mathematical over /undershoot). When comparing the equipotential <br />surfaces of the two models, the difference in head values is much more reasonable when <br />compared to observed drawdowns. If the drawdown model had been accurate, it would <br />have shown drawdowns equal the head differences between the two elevation models. <br />