2013-11-27_REVISION - M1990057

• Permit No: M1990057
• IBM Index Class Name: REVISION
• Doc Date: 11/27/2013
• Doc Name: Extension Request Amendment Review no 1
• From: The Union Milling Company
• To: DRMS
• Type & Sequence: AM1
• Email Name: MAC
• Media Type: D
• Archive: No

Mr. Michael Cunningham
CDRMS
November 26, 2013
6.3.3 Exhibit C - Mining Plan
5. The Division is currently reviewing Technical Revision No. 4 (TR -04) which addresses
changes to the TSF liner and leak detection system. Please revise all applicable portions
of Exhibit C that change as the result of the approval of TR -04.
Response: The following changes will be made to Exhibit C:
Section 4.3.2 Subgrade Preparation. Insert new bullet No 11.
"Install Geocomposite Drainage Layer (GDL) between embankment and
Geocomposite Clay Liner (GCL) to protect GCL during installation."
(new) Section 4.3.4 Geocomposite Drainage Layer
"A US Fabrics, Inc 220GN Geocomposite Drainage Layer, or equivalent, will be
placed on the interior slopes and bottom where there are seeps to protect the
GCL from premature hydration during the installation process. The GDL will be
installed concurrently with the GCL, leak detection system, and polypropylene
geomembrane liner. GDL specifications and installation instructions are
presented in Appendix 4 -1.4, Geocomposite Drainage Layer." (See Attachment
8)
Appendix 4 -1.4 will be added to Exhibit C.
• Section 4.3.5 Leak Detection System. Change last sentence in third
paragraph.
"If ground water is detected (indicating a leak in the GCL), the level will be
monitored, a small pump will be installed in the PVC pipe, the ground water will
be pumped to the impoundment, and the Division will be notified within 48 hours
from first detection."
Section 4.3.8 QA /QC, Onsite Personnel. Change to read:
"UMC's mill manager or qualified designee will be on site at all times
construction activates are being conducted by UMC crews or by contractor
crews. UMC has retained an Owner's Engineer, who is a Registered
Professional Engineer and a Professional Land Surveyor in the State of
Colorado, to monitor the contractors. UMC has contracted clearing and
grubbing, topsoil removal and storage, impoundment excavation and
embankment construction. UMC will contract GDL & GCL liner installation, leak
detection installation, sump construction, and impoundment liner installation to
complete the TSF project. UMC crews will place historic tails in the TSF,
construct and place ballast tubes on the impoundment sides, install tailings slurry
pipes to the impoundment, and install the decant water pumping station."
Section 4.3.8 QA /QC, Sub Base Construction, and Geosynthetic Clay Liner
Installation
• Change subheading to "Sub Base Construction, GDL and GCL"
• Insert new bullet No 2.
"The sub base will be constructed during a period of low flow to ensure
that the GDL will protect the GCL from premature hydration."
• Insert new bullet No 3.
"Liner contractor will install and test the geocomposite drainage layer in
accordance with manufacturer's recommendations. Installation of the