2011-08-08_REVISION - M1977493 ‎(33)‎

• Permit No: M1977493
• IBM Index Class Name: REVISION
• Doc Date: 8/8/2011
• Doc Name: EPP Submittal
• From: Climax Molybdenum
• To: DRMS
• Type & Sequence: TR18
• Media Type: D
• Archive: No

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Technical Revision (TR -18) Climax Molybdenum Company
Environmental Protection Plan Permit No. M- 1977 -493
technical and economic feasibility. As described in Exhibit D of Permit Amendment Application AM -06,
overburden placement will consist of additional placement in the area of existing E and F dumps as well
as the existing McNulty OSF. The scheduling /sequencing of overburden placement is being performed
during the summer of 2011 as part of ongoing mine plan evaluations. This investigation and design work
is focused on geotechnical stability, but will also include the development of a stockpile operations and
monitoring plan. The operations and monitoring plan is anticipated to include recommendations and
guidelines for overburden placement, which will be used in the development of EPFs for the OSFs.
Seepage collection and run -on and run -off control facilities are identified as EPFs (see Section T- 5.3.2) at
these locations to minimize the impact of potential acid drainage associated with these facilities. Designs
for these EPFs will be submitted prior to the initiation of construction in accordance with Rule 7.3.
The acid - forming materials will remain in -situ at the Climax site following final termination of mining and
processing activities. As discussed herein, as long as acidic drainage with the potential to affect the
environment is released from these sources, such drainage will be managed according to the stipulations
and requirements of the appropriate regulatory permits in place at the time.
T - 4.1 Temporary Cessation /Pro /ongedLack of AlMera/ Production
Surface water discharge at Climax is regulated under the CDPS Permit as discussed in Section T -2.2.
Under temporary cessation or a prolonged lack of mineral production scenario, mine waters, storm water,
and seepage waters would continue to be managed, treated and discharged according to the conditions
of this permit.
T - 4.2 Rim/ Closure
Upon final closure and reclamation of the Climax Mine as described in the Permit, Technical Revisions,
and Amendments, impacted waters from the mine, ponded water on the TSFs, seepwater from TSFs and
OSFs, and storm water will be managed according to conditions of the CDPS Permit. This permit
acknowledges that surface water from Climax must meet effluent limitations prior to discharge.
As described in Exhibit E — Reclamation Plan to Permit Amendment AM -06, both Tenmile and Mayflower
TSFs will be reclaimed with a combination of dry and wet covers. Due to concerns regarding water
treatment, flood control, constructability, and dam safety, a wet cap is needed for the Climax Mine site.
The flow rate of impacted water requiring treatment at Climax currently ranges from about 3,000 gpm
during the winter to about 40,000 gpm during the peak of the snowmelt period. Climax manages water to
reduce the volume and flow rate of water requiring treatment. This management includes the use of
interceptor canals, diversion ditches, surface treatments, and reclamation of formerly impacted land. The
seepage from TSF dams and water pumped from the open pit or underground mine workings, however,
will continue to require treatment well into the future. These future sources of impacted water are
expected to follow a similar pattern of significant seasonal variability. The use of a wet cap reclamation
scenario provides detention storage capacity that allows for seasonal attenuation during the peak flow
periods and promotes a more constant flow rate for water treatment. This detention storage dampens the
peaks of the impacted water hydrograph and reduces the required capacity of the treatment system. In
addition, an active reservoir to store impacted water provides flexibility in the timing and rate of water
treatment and therefore reduces the risk of releasing impacted water during an upset scenario in the
water treatment system or under unusual hydrologic conditions.
Hydrologic flood studies indicate that peak flow rates onto the TSFs are generally in the thousands of cfs
during a PMP event. If there is no detention storage capacity within the TSF to attenuate these flows,
which would be the case in a dry cover scenario, then very large and heavily armored channels would be
required to convey the flood flows safely beyond the site. The detention storage capacity provided by the
wet cover configuration allows for much lower capacity flood conveyance facilities. The detention concept
is less sensitive to peak flood flow estimation and results in lower risk from erosion, channel failure, and
potential dam breach.
The wet cap configuration also is consistent with that presented to DRMS and approved in Technical
Revision TR -13. The wet cover already established on the Robinson TSF is currently developing into a
sustainable mosaic of mesic, wet meadow, and emergent marsh habitats which support a variety of
EPP: Revision R1
T -12 July 2011