REP41419 - Laserfiche WebLink

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• SURFACE WATER HYDROLOGY CEC will implement a dewatering scheme for Sediment Pond 2 in 1997. When appropriate, Coors personnel will pump excess runoff water accumulated in this pond back to the Dugout Pond, which is located about 700 feet slightly upgradient and to the south-southeast on CEC property. The Dugout Pond is designated as an on-site permanent impoundment and has an available storage capacity that exceeds the total contributing runoff volume associated with a 100-year, 24-hour design storm (refer to "Technical Revision Drainage Control Plan II," dated January, 1995). A bank of pumps (maximum combined sustained pumping rate of 1200 gallons per minute (gpm)) will be used to evacuate the accumulated runoff water in Sediment Pond 2 back to the Dugout Pond within a maximum time frame of 72 hours, thus meeting a reasonable evacuation time period for the Sediment Pond 2 dewatering. Also, in this manner, Coors can maintain a continued lowered pond level in Sediment Pond 2 during prolonged periods of excess rainfall and runoff on site such as was experienced during 1995. Since the sediment level in Sediment Pond 2 has been virtually non-existent to very little after eleven years of use, and since this pond facility has never had any measurable water stored in it for more than a 24-hour period, except during the unusual prolonged period of excess precipitation events in 1995, and during which time period there was never any observed spillway discharge, all previously existing man-made temporary pond sites have been removed for CEC Plan purposes. The Dugout Pond, however, remains as a permanent pond. The CEC site drainage plan and facilities are presented in Appendix K, "Technical Revision Drainage Control Plan II," dated June, 1994. Existing diversion/drainage ditches that have been constructed along the access and haul roads and around the north and east sides of the CEC property presently serve to convey surface water runoff to Sediment Pond 2. The existing drainage facilities, as well as existing site topographic features, are shown on the Existing Surface Features Map. It is noteworthy that total long-term sediment accumulation in Sediment Pond 2 has not been a problem in eleven years of use (refer to previous discussion). The Dugout Pond shall remain undisturbed at site closure in order to provide a continued wildlife habitat, in accordance with DMG direction. The permanent drainage facilities for final site reclamation are shown on the Final Reclamation Contour Map and Drainage Plan drawing. AHR-1996 -78-