PERMFILE49068 - Laserfiche WebLink

Home Browse Search

Mr. Alec Schatz April 13, 2006 Page 2 area of the wetlands and thus gain even further control over the local drawdown conditions, but we expect that, especially for the easternmost wetland area, there will still be significant problems as one gets closer to the western edge of Pit I. The model outputs allow for determination of the magnitude of dewatering required to maintain the water level at the base of the upper sand and gravel deposit. Comparing the pumping rates required with and without the recharge is useful. With the recharge an estimated pumping rate of 15,700 gallons per minute ("gpm") is predicted. With the recharge in place, and balanced so as to minimize any flooding of the wetland cells simulated in the model, the predicted dewatering rate required increased to approximately 35,800 gpm, more than doubling that required for the no-recharge simulation. The rate of rechazge required for this simulation was somewhat less than the actual dewatering rate and was predicted by the model to be approximately 24,850 gpm. Note that adjusting this rechazge upward in the areas closest to Pit I would be expected to improve the final configuration somewhat. The change in the impacts on the river are significant. Absent the rechazge, the model predicted leakage from the river into the model is approximately 10,400 gpm, With the rechazge this drops to 7,500 gpm. Note that this represents only the model output for total leakage out of the model river cells and not the actual net impact on the river (model predicted inflows less the outflows) as was discussed in the earlier report. Simulations of Pit II with Pit I flooded have also been carried out. The presence of the large reclaimed Pit I open water body does aid somewhat in maintaining the water levels in the wetland area. However, the steep gradient seen in the Pit I simulations is again observed along the northeastern edge of Pit II and it is likely that even higher levels of dewatering may be required to provide sufficient drawdown to allow for efficient mining operations and to allow for the maintenance of the wetlands. In the modeling scenarios carried out we did not simulate the other small wetland azea located along the southwest side of the Phase VI and V pit areas. It is fully expected that for the earlier pits there would be excess dewatering water available to discharge to this area to maintain the local water table with little difficulty. With the later phases of mining it is expected that a similar steep gradient will be established and that similaz very high dewatering pumping rates will be required to maintain effectively dewater the pit. Once again, we expect that it will be quite difficult to fully protect the wetlands while effectively dewatering the pits. In the course of this modeling work we also looked a[ the drawdowns predicted along the runs of the two ditches that either cross of are adjacent to the property. In both cases there are significant drawdowns predicted absent any rechazging to the water table. We do not know what level of leakage these ditches exhibit and thus cannot at this time make any specific determinations as to the impacts of drawdown on the potential rates of leakage. What is clear, however, is that, without recharge, there will be significant drawdown impacts along the ditches, especially with regard to the Last Chance ditch as it enters the property from the southwest and Martin and Wood Water Consultants, Inc.