2011-08-08_REVISION - M1977493 ‎(36)‎

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

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Water Quality Monitoring Plan Climax Molybdenum Company
Version: R1 Permit No. M- 1977 -493
Robinson Lake indicated that groundwater is present close to the ground surface and that
alluvium in the valley consists primarily of silts, sands, and gravels. The alluvium overlays
bedrock consisting of the Minturn Formation and Tertiary -aged quartz monzonite intrusives.
The hydraulic properties of the Minturn Formation were determined from field packer tests
conducted in open borings. A total of fifteen tests were conducted in four borings. The results of
the packer tests indicate that the hydraulic conductivity of the Minturn Formation ranges from 0
to 2900 ft/yr, with an average conductivity of 480 ft/yr. (Kumar & Assoc., 1994). Hydraulic
properties of the overlaying alluvium were not measured, but the hydraulic conductivity of sands
and gravels typically range between 1,000 to 1 x 10 ft/yr (Freeze and Cherry, 1979). As in the
other drainages at Climax, the bedrock topography controls the direction of groundwater flow.
Groundwater flow in the valley is also influenced by the presence of three surface water bodies:
Chalk Mountain Reservoir, Robinson Lake, and Eagle Park Reservoir. Each of these reservoirs
was constructed by excavating and building an engineered dam to impound water.
Construction records for each dam indicate that a low permeability cut -off wall was excavated
into the underlying bedrock to control groundwater. Cut -off trenches under each dam present a
physical barrier to groundwater flow. Therefore, significant and continuous groundwater flow in
the alluvium and bedrock throughout the valley is unlikely as groundwater flow is intercepted by
the reservoirs.
Eagle Park Reservoir is privately owned and is located above the East Fork of the Eagle River
and below Climax facilities (Figure 1). Seepage emanating from the toe of No.4 Dam is
collected in a collection sump keyed into bedrock and pumped back to Robinson Lake. The
average, intermittent pumping rate for the sump is approximately 10 gpm which reflects the low
rate of groundwater flow in this area.
3.2.5 Monitoring Sites
3.2.5.1 POC Monitoring Site
A POC monitoring well will be established near the Climax property boundary between No. 4
Dam and the Eagle River. A proposed location for this new well, identified as EVMW -3, is
presented on Figure 3; however the final location will be determined through site
reconnaissance and subsurface investigations. The well will be constructed during the 2011
field season and will be completed in alluvium and /or shallow bedrock, depending on water
table depth. Baseline water quality will be established for a two -year period at this site. Section
4 of this Plan describes the monitoring at this POC location.
3.2.5.2 Internal Monitoring Sites
Climax will monitor several internal sites located above Eagle Park Reservoir (Figure 3). In
addition to the protection afforded to Eagle Park Reservoir by the Environmental Protection
Facilities (EPFs) described in the EPP, these internal water monitoring sites will enable
detection of potential changes in water quality upgradient of the reservoir so that appropriate
actions can be taken.
Groundwater quality within the upper Eagle River Valley has historically been monitored
quarterly at the EVMW monitoring well (Figure 3) which was constructed in September, 1993. A
well log for the EVMW is in Appendix B. EVMW is located above Eagle Park Reservoir,
approximately 200 feet downstream from the Robinson Lake Seepage Collection system.
EPP — Appendix C
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