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
contain and collect impacted seepage from the downstream toe of Robinson Dam and convey this water
back into Robinson Lake. This EPF became necessary when Eagle Park Reservoir was converted to a
clean water reservoir in 1997. This EPF was constructed in 1997 and significant modifications were
made in 2001. The system has been in continuous operation since 1997.
The primary means of containment consists of a concrete cut -off wall below the Robinson Dam outlet
area that is keyed into bedrock on the bottom and sides. A collection pond located on the upstream side
of the cutoff wall provides detention storage and emergency storage capacity in the system. The
collection pond provides an operational capacity of approximately 400,000 gallons. Captured seepage
and runoff from the downstream face of Robinson Dam is pumped back into Robinson Lake. This cutoff
and containment component restricts groundwater seepage from entering Eagle Park Reservoir.
The Robinson Lake Seepage Pump System includes a pump station that houses two submersible pumps
that each have a capacity of approximately 480 gpm operating individually and approximately 750 gpm
operating in parallel. The second pump functions primarily as an installed spare. The operation of the
pumps is automatic based on the water level in the collection pond. There are two discharge pipelines,
one operating and one backup, that convey the water from the pump station to Robinson Lake.
The pumping system is electrically powered. Additional backup systems include a diesel generator
installed at the site that can be activated in the event of a sustained loss of power. There are also diesel
powered pumps on site that can be used in an upset condition to pump water from the collection pond
into Robinson Lake. The system also includes instrumentation and telemetry that will activate alarms at
the mill facilities in the event of a high water level in the collection pond. The system is inspected by
Climax personnel daily.
Typical seepage rates from Robinson Dam are in the range of 20 to 50 gpm, which is much less than the
pumping capacity of the system. This is the normal inflow rate to the system. However, since the system
collects surface runoff from the small tributary basin above the cutoff wall, the design capacity of the
system is controlled by hydrologic events such as rainfall or snowmelt. The hydrologic design basis of
this system is the 100 -year 24 -hour precipitation event or the 100 -year snowmelt event occurring within
the basin that is tributary to the seepage collection system.
4 Dam Seepage Collection and Pump System: The lowermost EPF downgradient of Climax facilities that
protects the East Fork of the Eagle River beyond and below the Climax property boundary is the 4 Dam
Seepage Collection and Pump System. This EPF is located just below the Eagle Park Dam (a.k.a. 4
Dam) and consists of a seepwater collection pond and two pumps in the adjoining enclosed pump house
to return seepage to the upstream Robinson Lake. Located directly below the pump -house is a second,
smaller seepage collection pond that acts as secondary containment of the seepage. This second pond .
supports a small pump that returns seepage back to the first collection pond. The discharge pipeline for
the system extends from the pump station along the south side of Eagle Park Reservoir to the discharge
point at Robinson Lake.
The intent of the collection system configuration is to minimize the collection of surface runoff from the
downstream face of the dam. This surface runoff is not impacted by mine materials and can be routed to
the stream system. Seepage from the dam toe is contained and routed into the collection pond.
Backup systems in place at this EPF to prevent discharge of impacted water to the East Fork of Eagle
River include an installed backup pump and a diesel generator for use in the event of an extended loss of
power. Instrumentation and telemetry equipment is in place to trigger an alarm at the mill facilities in the
event of a high water level in the collection pond.
Robinson Lake Pump System: The location of the new Robinson Lake Pump Station is just below
Robinson Dam. The former pump station facility in this location has been decommissioned. The new
Robinson Lake Pump Station and reclaim water pipeline are part of the process water reclaim system
allowing for the recycling and re -use of water from the TSFs. Water will be pumped to the mill water
storage tank through a 21,000 foot buried steel pipeline for use as process water in the milling circuit. As
described above, recharge to Robinson Lake will be accomplished by transferring water from Tenmile
TSF and Mayflower TSF via the Tenmile Tunnel. The new pump station has a nominal operating
capacity of 10,000 gpm. The Robinson Lake Pump Station and pipeline design was submitted to, and
approved by, DRMS in 2008 under TR -14 and later in 2011 under TR - 17 due to a change in pipeline size
EPP: Revision R1
T -20 July 2011