2002-03-04_REVISION - M1986015 (8)

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MINING PLAN Dewatering Because most or all of the area will be mined prior to constructing the slurry wall, dewatering will be required. Some the water generated in the dewatering operation will be used as a source for wash water, but it is unlikely that all the water that will be exposed by the mining can be used in the washing. Figures 1 and 2 show the dewatering and processing circuits. Figure I shows a possible layout using actual conditions on site. Figure 2 shows the initial and the alternate (optional) post-initiation circuits in a more diagrammatic fashion. Initially, water from the pit (dewatering water) will be pumped across the large drainage and discharged into a sequential vegetation and lake settling system before it is discharged to the river. It has been estimated that dewatering will require pumping between 2000 and 3000 gallons per minute. This is very close to the amount of water that will be continuously discharged back to the river from the sediment and discharge system. Wash water for the processing of gravels will be derived from the lake near the river. This will be pumped to the plant in a separate, closed line. It is estimated that processing of the gravel will require about 3500 gallons per minute. Thus, when washing is occurring, it is possible that the discharge system lake near the river will be drawn down to the point where no discharge to the river will occur. But this draw down should only occur until the return water from the plant reaches the lake. Water from the washing operation at the plant will be pumped to the east side of the drainage channel and into a sediment basin. That sediment basin will then connect to a second sediment basin. It is expected that most of the heavy sediment will remain in the first sediment basin. Some of that sediment will probably make it into the second basin as well, but the second basin will allow some of the finer particles to be settled. Water from the second basin will then discharge southward to join the dewatering water. This will roughly double the volume of water entering the lake. But because the amount of water removed from the lake for washing will be very slightly (roughly 4%) more than the amount introduced from washing discharge, the lake will actually remain fairly stable and will discharge an amount of water about equal to the amount introduced into the system from dewatering. Therefore, the water level in the lake, although it may fluctuate perhaps a foot or two during the day for short periods, will remain at very nearly the same level for most of the time. Also, by blending water coming from the double sediment settling system with much cleaner dewatering water, the water entering the lake will remain relatively clean and thereby aid in complying with discharge requirements. Pueblo East Pit Amendment xhibit Page 8