PERMFILE68068

• Permit No: m2004044
• IBM Index Class Name: Permit File
• Doc Date: 12/22/2004
• Doc Name: Reclamation Cost Estimate and Pit Wall Stability Analysis
• From: DMG
• To: DMG
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
7313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
DATE: December 22, 2004 `~
COLORADO
DIVISION OF
MIN SRALS
GEOLOGY
0.EClAM AT~ON•MINING
SAf ETY•SC IENCE
Bill Owens
Governor
TO: Larry Oehler ~ Russell George
Executive Director
FROM: Allen Sorenson~~ / Ronald W. Cattany

~ Division Director
y Natural Resource Trustee
RE: Reclamation Cost Estimate and Pit Wall Stability Analysis, Aggregate Industries,
Tucson South Resource Gravel Pit, File No. M-2004-044
The Division of Minerals and Geology (DMG) engineering staff has reviewed the revised stability
analysis and proposed setbacks provided by the Applicant in a submittal dated November 22, 2004.
Staff has also reviewed draft specifications for slurry wall construction provided in that same
submittal. DMG concurs with the results of the revised stability analysis and with all of the
proposed mining setbacks, save one. The proposed 50-foot setback from the north side pipeline is
insufficient to assure that the structure will not be damaged. However, in the November 22, 2004
submittal it is stated that the Applicant has a setback agreement with the owner of the pipeline. In
order to mine to the proposed 50-foot setback, DMG must be provided a copy of the agreement and
the agreement must meet the requirements of §34-32.5-115(4)(e), C.R.S.
It is noted on the mining plan provided with the November 22, 2004 that in the absence of an
agreement with the owner of the north side pipeline that the pit slope will be mined at 0.67H:1 V,
which would be stable. Mining at this prescribed angle will be problematic due to equipment
limitations and the mechanics of earthmoving. Mining at steep pit slope angles cannot be
accomplished with dozers pushing down the slope, nor can it be done using scrapers traversing the
slope. Mining at the toe of the slope with afront-end loader does not allow for effective control of
the slope angle. Raking material down the slope with an excavator would allow for slope control,
as would benching down from the surface using scrapers or dozers. However, these are relatively
inefficient mining methods that are rarely observed by DMG inspectors in the field. Another
concern is that the requirements to mine at prescribed slope angles may not be communicated from
the permit requirement, through company management to pit supervision to the equipment
operators. Although the DMG has in the past approved and will approve a mine plan using a
prescribed pit slope angle protective of structures, the Applicant must be awaze that if this is the
compliance mechanism employed, it will be considered a serious violation of the permit if through
inspection or otherwise it is determined that mining has occurred at angles steeper than those
prescribed. The Applicant should reconsider the selection of a compliance method that requires
mining the pit slope at a prescribed angle. If the Applicant chooses to stay with this compliance
method, they must describe in detail and in terms of the mechanics of eazthmoving how these pit
slope angles will be maintained in the field. Otherwise, revised setback distances should be
provided based on stability under a vertical highwall condition.
Office of Office of Colorado
Mined Land Reclamation Active and Inactive Mines Geological Survey