2012-11-09_REVISION - M2010049 (3)

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Western Sugar Reclamation Land Development Project Flood Analysis typical of large storm events. With such an occurrence, it is likely that flood threats would be issued well in advance of flows that have the potential to flood the Site. Once flood threats are issued, Varra Companies, Inc. will shut down dewatering pumps for Tract C allowing the pit to fill. Even with no flood inflow, the pit would fill in approximately 3.5 days due to groundwater inflow. And once the pit is full, headcutting and erosion would not occur because of minimal water surface elevation difference between the floodplain and the pit - eventually the two will be equal. VII. TRACT D Per the September 21, 2012 meeting between Varra Companies, Inc and DRMS, it was agreed that due to the relatively small volume of Tract D, it would fill prior to possibility of headcutting back to the river. The WinDAM B model results for Tract C berm width also apply to Tract D, and being that those results indicate that headcutting from a 100 -ft berm is unlikely for Tract C, it would be unlikely for Tract D also — especially considering a much shorter fill time for Tract D. VIII. FLOOD RECESSION BACK INTO THE RIVER AND BANK EROSION Headcutting and bank erosion as the flood recedes is not a concern. This includes flows from the dewatering ditch that runs between Tracts C and D. As the flood recedes, the river and floodplain water surface elevations will decrease at the same rate because they are essentially a "pool." Thus, an elevation gradient will not exist between the floodplain and river which would be necessary for headcutting and bank erosion. IX. HARD AMORING AS AN EXTRA LEVEL OF PROTECTION AGAINST CAPTURING THE RIVER Analyses such as above can not conclusively predict that the pit will erode back to the river. — it is impossible to truly predict natural events occurring in nature. However, the results do add a high degree of confidence that headcutting will not occur back to the river and thereby capture it. Because of uncertainties, an extra level of protection will be added to the Site post mining as agreed upon during the 9/21/2012 meeting between Varra Companies, Inc and DRMS. That protection will include lining a section of Tract C between the pit rim and river with overtopping protection (as would be done for an embankment dam) at the breakaway section between Oglivy Ditch Diversion Dam and Ash Avenue. Such protection will extend from the pit rim to the normal high water mark of the pit reservoir. Overbank hard armoring protection will be discussed in detail in a separate document provided by Varra Companies, Inc. Also, hard armoring protection will be placed around the gas battery in the northeast corner of Tract C. This design will be discussed in detail in another document provided by Varra Companies, Inc. p9. 11