2013-07-09_REVISION - C1981010 ‎(7)‎

• Permit No: C1981010
• IBM Index Class Name: Revision
• Doc Date: 7/9/2013
• Doc Name: Proposed Decision and Findings of Compliance
• From: Trapper Mining Inc
• To: DRMS
• Type & Sequence: RN6
• Email Name: JLE
• Email Name: SB1
• Media Type: D
• Archive: No

sediment control plan boundaries. Given this, the Division proposes to approve
the renewal application (RN -6) with the following stipulation:
Stipulation No. 21:
THE OPERATOR MUST SUBMIT AND RECEIVE APPROVAL FOR A
PERMIT OR TECHNICAL REVISION TO UPDATE THE DRAINAGE AND
SEDIMENT CONTROL PLAN PRIOR TO ANY DISTURBANCE OUTSIDE
OF THE CURRENTLY APPROVED DRAINAGE AND SEDIMENT
CONTROL PLAN BOUNDARY.
D. Surface and Ground Water Monitoring
The applicant will conduct monitoring of ground water in a manner approved
by the Division. The ground water monitoring plan can be found in Section
4.8.5.2a, Vol. IV of the permit application (4.05.13(1)).
2. The applicant will conduct monitoring of surface water in a manner approved
by the Division. The monitoring plan was submitted under 2.05.6(3)(b)(iv)
and can be found in Section 4.8.5.1a of the permit application, Vol. IV
(4.05.13(2)).
The Division has reviewed the surface and ground water monitoring plans as part
of the renewal process. These monitoring plans are adequate to monitor for the
development of impacts, if any should develop. Well GP -09 has been designated
the groundwater point of compliance for the Third White Sandstone aquifer and
the Coy well is the point of compliance for the Flume Gulch Alluvium.
No new or revised water monitoring is being proposed under RN6.
E. Probable Hydrologic Consequences
The model for leachate formation and migration at the Trapper Mine is based on a
study conducted by the U.S. Geological Survey at the Seneca II Mine in Routt
County, approximately 14 miles east of the Trapper Mine (U.S. Geological
Survey Water Resources Investigations Report 92- 4187). The model is described
in the probable hydrologic consequences of the permit application (section 4.8),
and is summarized below.
Ground Water Impacts:
Leachate formation - Slightly acidic snowmelt and rainwater at the Trapper
Mine infiltrates into the spoil that fills the reclaimed pits and fill structure (Horse
Gulch Fill). Groundwater may also seep into spoil from adjacent or underlying
rocks. As the water percolates through spoil, chemical reactions occur with the
spoil. The main reactions are dissolution, pyrite oxidation, and cation exchange.
Trapper Mine 24 July 9, 2013