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• Item 3: Attachment G - Pond cross-sections shows depth and capacities for sediment runoff, and freeboard. The 1008 sediment level is shown and the 608 sediment level has been added. The 10 yeaz, 24 hour runoff level and capacity in acre-feet aze also shown on attachment G. The backup calculations for attachment G can be found in Volume 9, Appendix B-6, Mt. Gunnison No. 1 Mine, Mining and Reclamation Plan. Item 4: The peak flow calculations for the 25 year, 24 hour precipitation event for Pond MB-5 as well as emergency spillway design calculations and data can be found in Volume 9, Appendix B-6, Mt. Gunnison No. 1 Mine, Mining and Reclamation Plan. Item 5: Calculations for detention time as well as a stage discharge curve for the proposed dewatering pipe are included herein. The dewatering device at MB-5 will be used as a oanbinaticn automatic/manual dewatering device. When water inflow meets dischazge effluent limitations the dewatering valve will beset at the calculated automatic setting which, based on sediment height, will provide 24 hour detention time for the 10 yeaz, 24 hour precipitation event. Please see the enclosed discharge curve vs, sediment height for • automatic dewatering. The valve will beset at the appropriate flow based on sediment height. The flow will be read from the flow meter. The minimum flow @ 1008 sediment storage is 42 GPM and the maximum flow @ 08 sediment storage is 102 GPM. Based on these numbers when the dewatering device is set for automatic de- watering it should be able to keep up with groundwater inflow. 'Ib better illustrate this point a oamparison can be made between the flows from the proposed dewatering device and pumping of MB-5 which was carried out in the Spring of 1986. A small sump pump was used at MB-5 much of May and June, 1986 to dewater MB-5. This pump was rated at a maximum capacity of 50 GPM which is neaz the low end of the range for the automatic dewatering pipe. This sump pump was able to lower the level of MB-5 and stay ahead of groundwater inflow during the peak flow period of Spring runoff for both surface water and groundwater. The Spring runoff period corresponds with maximum groundwater inflow to the pond (MB-5). if groundwater inflow remains near the 1986 Spring flow or even increases slightly the automatic dewatering device will be able to maintain sufficient discharge to dewater the pond. •