2010-08-05_REVISION - M1977493

• Permit No: M1977493
• IBM Index Class Name: REVISION
• Doc Date: 8/5/2010
• Doc Name: Letter to Mr. Paul Perri, P.E.
• From: Climax Molybdenum
• To: DRMS
• Type & Sequence: TR16
• Email Name: ACS
• Media Type: D
• Archive: No

Climax Molybdenum
A Freeport-McMoRan Company
July 23, 2010
Paul Perri, P.E.
Design Review Engineer
Safety of Dams Program
Division of Water Resources
1313 Sherman Street, Room 818
Denver, CO 80203
RE: Robinson Reservoir, DAMID:370107
Dear Paul:
Climax Mine
HWY 91 - Fremont Pass
Climax, Colorado 80429
Phone [phone]
Fax [phone]
Thank you for coming up to review our planned cleanout of Robinson Lake. The background, project
objective, and plan to ensure dam safety is included below.
Background
Robinson Reservoir is located on the Climax Mine property in the Eagle River drainage. The reservoir
was constructed in 1936 as process water storage for mining operations. The embankment was raised
in 1956 to increase process water storage volume available. The current water storage volume in the
reservoir is approximately 3,136 acre-feet.
Influent water quality to the reservoir was such that treatment by the addition of quicklime (CaO) and fly
ash was necessary to maintain pH and metals concentrations in the water pool for use in the milling
and floatation circuits. Over the years, a significant amount of lime and metal hydroxide sludge was
deposited in the reservoir which reduced available storage capacity. The total sedimentation due to
this deposition is estimated at around 1.0 to 1.3 million cubic yards (620 to 806 acre feet) which directly
impacts the amount of process water storage available in the reservoir. Thus the available water
storage in the reservoir was limited to approximately 2,300 to 2,500 acre-feet due to this sediment
accumulation.
Approximately 640,000 cubic yards of sediment, topsoil and sub-soils were removed in 2008 which
increased available storage by 400 acre-feet. Current estimates place the remaining sludge volume
that is accessible by standard earthmoving equipment at approximately 800,000 cubic yards. In order
to remove the sludge materials, additional underlying topsoil and sub-soil will have to be removed in
order to operate equipment in the excavation area. The underlying topsoil and sub-soil that will require
recovery is approximately 200,000 cubic yards.
Project Objective
The objective of this project is to accelerate the removal of the remaining accumulated lime and metals
sediments in order accelerate reclamation of this area as well as to reclaim process water storage
volume lost in the reservoir and ensure adequate storage in the reservoir for future operations.
An additional objective of this project is the salvage of underlying native materials and subsequent use
of this material for reclamation purposes. Based on previous experiences removing the sediments in