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of Phase 1. The inlet to this pump will have a gravel filter of 3' width on all sides to prevent the pumping of silty water. A float control device will be located in Trench #1 to control a pump lo- cated at the north end of the sediment pond to feed water in the trench if it falls below the desired level of 4452 to 4458'. This level is approximately 4 to10 feet above the existing groundwater level. Initially, the water level in the trench will only be raised to 4 feet above the existing water level. If ongoing water monitoring shows undesirable movement of the contaminant plume in any direction, the water level will be adjusted in the trench to get the desired stability of the plume. The CDPHE fumly believes that the existing monitoring well layout and sampling program is more than ade- quate to keep the plume in place without any significant movement. Their past testing of the plume has shown very little movement in many yeazs. The installation of the trenches and maintenance of the correct water level should continue to keep the plume in its place. The inlet to the pump to Trench #1 will have a 3' wide gravel filter or other pre-fabricated filter so that all water entering Trench # 1 is free of silt, thereby preventing the Trench from becoming less permeable due to siltation. If a sheen is detected in either the pit, sediment pond or the trenches, a petroleum absorbent "pig" will be placed around all pump intakes. Trench #1 will have an adjust- able metal gate spillway set at a desired elevation so that water above this elevation will enter Trench #2. In this manner, high water levels in the trenches will always be maintained to try to keep the contaminated plume to the north of the site. This arrangement will probably result in more in- flow into the pit, which will require more pumping, however, it is seen as the best solution to en- sure that the contaminated plume does not migrate south into the permit azea. The sediment pond will utilize a pump that will allow water to flow in an overland dischazge pipe to the Colorado River as shown on Map C-2. FMM has a NPDES permit to dischazge pit water at this location and significant monitoring requirements accompany this dischazge. This permit is in- cluded in Appendix D. A rip rap apron of approximately 8' x 10' in size utilizing minimum size of 12" riprap will be installed at the request of the landowner so that this dischazge does not erode the bank. The landowner, State Division of Pazks and Recreation, has also included a letter stating that they desire for this rip rap apron to remain after mining to provide a logical place for them to direct dischazge to the river and also to protect against erosion in the north branch of the river. This letter Gilsonite Pit 9/03 10