PERMFILE139826

• Permit No: M1999050
• IBM Index Class Name: Permit File
• Doc Date: 6/21/1999
• Doc Name: RESERVOIR LINING PLAN CONNELL RESOURCES TIMNATH CONNELL PIT FN M-99-050
• From: DMG
• To: GREGG SQUIRE
• Media Type: D
• Archive: No

• III IIIIIIIIIIIIIIII i
STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1317 Sherman 51.. Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
DATE: June 21, 1999
DIVISION OF
MINERALS
GEOLOGY
RECLAMATION
MI NING•SAFETY
TO: Gregg Squire Rill O~rvens
Governor
Greg E Walther
FROM: Allen Sorenson•~~ Executive Director
Michael B. long
Division Direcor
RE: Reservoir Lining Plan, Connell Resources, Timnath Connell Pit, File No. M-99-050
The following issues were identified during a review of the permit application for the Timnath Connell
Pit and remain to be addressed for the Division to recommend approval of the application. This review
was limited to assessing exhibits to the application intended to assure that reclamation would achieve
the post mining land use of developed water resources as a lined pit, to assessing the stability of
structures within 200 feet of the pit, assessing impacts to the water table, and long term stability of [he
reclaimed pit.
The Division can stipulate to the stability of the reclaimed 3: I reservoir slopes both when the
reservoir is filled and during rapid draw down. However, the applicant should rescind the
statement in Exhibit E that slopes more than 10 feet below or 5 feet above the water line may be
constructed at 2:1. This would not appear to be a hardship in that the pit is planned to be 16 feet
deep. The applicant must provide a demonstration that the depth to bedrock will not
significantly exceed 16 feet in any areas of the pit's perimeter. This demonstration is necessary
to evaluate pit slope stability and backfill volumes for bonding purposes.
2. The analyses provided in the application do not consider [he stability of highwalls created
during mining and prior to backfilling; nor do the analyses examine the potential for adverse
impacts on structures within 200 fee[ of the limits of mining. The applicant should provide
stability analyses for the critical pit cross-section that would occur during mining or obtain
compensation agreements with the owners of structures within 200 feet. If a stability analysis
were provided absent shear strength testing of the soils and bedrock, the Division would have an
issue with the soil properties listed in Table 1 to the Slope Stability Analysis section of the
application. The alluvium friction angle of 32 degrees would be acceptable, and the bedrock
strength should be analyzed considering the residual strength of [he material, which would be
much less than the strength listed in Table 1. Analyses considering the residual strength in the
bedrock should be further analyzed for non-circular failure surfaces.
The $1.25/c.y. unit cost in Exhibit L for installation of the compacted low permeability reservoir
slope backfill may be low. This cost should be evaluated considering the need to dewater the
work area, rip and excavate a keyway. rip and excavate a percentage of the backfill material
from the pi[ floor, to moisture condition and place the backfill in thin lifts, and to provide for