PERMFILE66992

• Permit No: M1999050
• IBM Index Class Name: Permit File
• Doc Date: 9/6/1999
• Doc Name: Conditions for Approval
• From: DMG
• To: DMG
• Media Type: D
• Archive: No

STATE OF COLORADO
DiVIS10N OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman 8t., Room 215
Denver, Colorado 80203
Phone: [phone]
fAX: [phone]
DATE: September 6, 1999
TO: Gregg Squire
FROM: Allen Sorenson
RE: Conditions for Approval, Connell Resources,
Timnath Connell Pit, File No. M-99-050
DIVISION OF
MINERALS
GEOLOGY
RECLAMATION
M7 N1NG•SA F£7Y
Bill Owens
Governor
Greg E. Walther
Executive Director
Michael B. Long
Division Director
• Based on a review of the responses to the Division's adequacy review, the following is a discussion of
the issues to be resolved through conditions placed on the application approval and a list of proposed
stipulations.
Ground Water Interception and Delivery
• The applicant has committed to the installation and operation of a ground water interception and
delivery system to maintain ambient water table elevations in the vicinity of the pit. This plan, if
properly installed, maintained, and operated, will be effective. However, the plan is qualitative and
may be difficult to enforce. For example, the plan states that "The six monitoring wells installed on site
will be used for monitoring ground water levels for the operation of the drain system," but provides no
criteria for triggering the routing of ground water or water pumped from the pit to either the infiltration
ponds or the river. It is my understanding that the Party to the Boazd's consideration of this application
is satisfied with the plan, thus providing a sound basis for the Division's recommendation to approve.
Slone Stability Issues
The applicant has provided stability analyses and recommended mining setbacks for the roads and
irrigation ditches at the pit. The applicant provides a justification for assumptions used in the stability
analyses that states, in part, that "The critical slope failure for a gravel highwall will occur in the gravel
and not in the bedrock." While the Division does not agree with the applicant's rationale relative to the
potential for bedrock failures, it has been determined that the proposed setbacks are adequate for
stability. It should be noted that although the irrigation ditches should be stable against slope failure
with the 25 foot setback, mining and dewatering within 25 feet may increase seepage losses from the
ditch. It is also important to note that the 35-foot setbacks specified for protection of roads are to be
measured to the right-of-way lines, not necessarily to the edge of the roadways. .
For future reference, a discussion of the potential for bedrock involvement in slope failures at gravel
• pits is provided here. When shale bedrock is unloaded by extraction of overlying material, stress relief