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POST FLOOD CONSIDERATIONS <br />When the existing tailing pond spillway system is plugged and abandoned, it will be <br />necessary to account for baseflow into the pond that could occur immediately after the PMF. <br />Also, without an unregulated spillway, an operational plan to reduce the amount of water <br />stored in the tailing pond to pre -flood conditions will be necessary. The following post -flood <br />considerations should be addressed. <br />• Stability of the tailing pond embankment under the high water level conditions that <br />would exist after the PMF. <br />• Repair and operation of the fresh water bypass systems after the flood. <br />• Methods for removal of the floodwaters from the tailing pond to restore the pond level <br />to pre -flood conditions. <br />• Allowance for additional inflow to the tailings pond that would occur after the PMF <br />event. <br />• Time required to remove the floodwaters from the tailing pond to restore the pond <br />level to pre -flood conditions, or to return the system to a condition where the flood <br />storage volume required is again available. <br />Tailing Pond Embankment Stability <br />The stability of the Henderson tailing pond embankment under high water level <br />conditions was evaluated by URS Corp. Their geotechnical report that addresses this issue <br />is included herein as Appendix B. The results of the stability analysis, which are described in <br />more detail in the URS report, indicate that the factors of safety representing embankment <br />stability would remain in the acceptable range under the flood condition. The condition that <br />was used in the URS analysis was a water level in the pond within one vertical foot of the <br />dam crest for a period of six weeks. This corresponds to a beach length of about 100 feet <br />assuming a slope of 1.0 percent. <br />Bypass System Oneration <br />The upper bypass system, consisting of the Ute Creek Reservoir Bypass, the <br />Horseshoe Bypass, and the East Branch Reservoir Bypass, generally consists of trash rack <br />protected inlets to buried pipelines. It is likely that these systems would not suffer significant <br />14 <br />