2014-10-27_REVISION - M1990057

• Permit No: M1990057
• IBM Index Class Name: Revision
• Doc Date: 10/27/2014
• Doc Name: Completion of Permit Requirements
• From: The Union Milling Company
• To: DRMS
• Type & Sequence: TR4
• Media Type: D
• Archive: No

• The pond excavation at a maximum 21ft depth has not impacted known aquifers at
80-100ft below the surface. Only minor drainage from a perched aquifer was
observed. UMC identified this issue to CDRMS, and design measures have been
approved for the installation of the liner and leak detection systems.
Is The TSF embankment will be constructed from available onsite soils borrowed
from the tailings disposal area as outlined in the recommendation of CTL
Thompson, Inc., Permeability Study, April 10, 1990, presented as Appendix 15-2,
and Slope Stability Evaluation, July 8, 2011, presented as Appendix 15-5 in the
permit document. Confirmed during site visit.
• The TSF will be constructed as a zero discharge facility with 3ft of freeboard in
accordance with the Probable Maximum Precipitation Estimates. The TSF design
addresses this and the embankment is constructed consistent with the design drawings.
• Non disturbed drainage is diverted around the TSF while disturbed area drainage
from the mill area disturbance reports to the TSF. This work is not yet completed.
The drainage design was developed by Curfman Engineering, Boulder Colorado and
approved by CDRMS as presented by UMC in Adequacy Review No. 4. 1 recommend
that CDRMS confirm during their inspection that the drainage has been completed
according to the approved design.
• The observation well down gradient from the 4.6ac TSF area will be maintained in
its current location and monitored. UMC has committed to constructing new up- and
down-gradient monitoring wells. The proposed locations of these wells were identified,
however they have not yet been drilled. I recommend that CDRMS inspect these wells
once they are complete.
• Topsoil, in accordance with the topsoil plan will be removed and stockpiled.
Confirmed during site inspection.
• Stability analysis initiated by CTL Thompson, Inc. These documents were reviewed.
• A 2.5:1 (horizontal to vertical) outside face and a 2:1 interior face embankment
dam with a berm 12ft wide at the crest. Confirmed during site inspection and review
of design drawings.
• A geosynthetic clay liner of 1 x 10-6cm/sec permeability (or less), or equivalent
material liner will be used for the TSF liner. This is not yet completed. The design is
consistent with standard industry practice and should be adequate for the intended use
of the TSF. I recommend that CDRMS inspect the liner installation during construction.
• A seepage/leak detection drainage net system between the geosynthetic clay liner
and the 45-mil polypropylene geomembrane with the collection sump located in
the northwest corner of the impoundment, and the pond bottom sloping at 0.5% to
the northwest. This is not yet completed, although the sump has been installed as
specified in the design. The design is consistent with standard industry practice and
should be adequate for the intended use of the TSF. I recommend that CDRMS inspect
the liner installation during construction.
• A synthetic pond liner of 45-mil polypropylene geomembrane or equivalent. This
is not yet completed. The design is consistent with standard industry practice and
should be adequate for the intended use of the TSF. I recommend that CDRMS inspect
the liner installation during construction.
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