2011-09-08_REVISION - M1977342 ‎(35)‎

• Permit No: M1977342
• IBM Index Class Name: REVISION
• Doc Date: 9/8/2011
• Doc Name: Additional Copies of 2010 Documents
• From: Climax Molybdenum
• To: DRMS
• Type & Sequence: TR14
• Media Type: D
• Archive: No

SCENARIO
IMPORTED
PUMPING
CAPACITY
TIME REQUIRED
TO
DEWATER SYSTEM
1
None
7.5 weeks
2
5,000 gpm
6 weeks
Post-Flood Storage Allowance
The timing assumptions described above are necessary to calculate a reasonable
storage allowance to account for baseflow entering the pond after the PMF event. This
baseflow would continue to increase the storage volume in the pond until the pond
dewatering systems, as described above, become operational. In addition, an allowance for
water that would infiltrate into the tailings impoundment through the normally unsaturated
beach area of the pond has been made. Using an infiltration value that is consistent with the
hydraulic conductivity used by URS in the seepage and stability analysis, we estimate that
about 10 acre -feet per day of the flood volume would infiltrate into the tailing sands after the
storm. As such, the post -flood storage allowance was calculated to be 288 acre -feet. This
value includes 328 acre -feet of baseflow that would continue to enter the pond during the four
days between the storm event and operation of the pump barge Tess 40 acre -feet that would
infiltrate into the tailing sands. Adding this allowance to the flood storage volume results in a
total flood storage requirement of about 3,582 acre -feet (3294 + 288). This amount of
storage must be available in the tailing pond and East Branch Reservoir for PMF detention.
Time to Dewater System
With the abandonment of the existing decant/spillway system, it will be necessary to
pump the floodwaters from the impoundment after the PMP storm. This would be
accomplished using the proposed barge pumping system, along with on -site and possibly
imported portable pumps. An estimate of the time required to remove the floodwater from the
pond is based on returning the flood storage capacity to that required for a follow-up storm of
the same magnitude. This amount would not include the 130 acre -feet allowance for the
failure of Ute Creek Reservoir, since it has already failed. The following table summarizes
two scenarios; one with and one without imported pumps. The imported capacity would be in
addition to the barge pumps and the three portable Climax pumps.
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