2009-08-18_PERMIT FILE - M2009048

• Permit No: M2009048
• IBM Index Class Name: PERMIT FILE
• Doc Date: 8/18/2009
• Doc Name: Review of Proposed Mining Setbacks
• From: DRMS-acs
• To: DRMS-thm
• Email Name: THM
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]

DATE:
TO:
FROM:
RE:
Allen Sorenson"/COLORADO
August 18, 2009 Ix
Travis Marshall el
D I V I S I ON OF
RECLAMATION
MINING
SAFETY
Bill Ritter, Jr.
Governor
Harris D. Sherman
Executive Director
Ronald W. Cattany
Division Director
Natural Resource Trustee
Review of Proposed Minini? Setbacks, Grand Junction Concrete Pipe Company,
Gunnison River Gravel Pits, File No. M-2009-048 --'
The Division of Reclamation, Mining, and Safety (DRMS) engineering staff has reviewed the above
referenced permit application and has determined that the following issues remain to be addressed relative to
the proposed mining setbacks.
The geotechnical stability exhibit included in the application illustrates a maximum pit depth of thirty
feet; twenty five feet of sand and gravel and five feet of overburden. The mine plan exhibit states that
overburden thickness throughout the pits varies from six inches to fifteen feet. The descriptions provided
indicate that the proposed pits have been drilled. The Applicant must provide drill logs or otherwise
describe the basis for the determination of a thirty foot maximum depth, as excavation depth is critical to
evaluation of the sufficiency of proposed setbacks.
2. It is stated in application that temporary excavation slopes will be 0.25H:1 V. Since it is difficult and
unnecessary to exercise precise control of excavated slopes of this steepness, the DRMS requires
evaluation of vertical slopes for establishment of setbacks.
3. It is stated in Exhibit D that overburden and topsoil will be stockpiled around pit perimeters, but no
vertical dimension or side slope angles are provided. The general stability analyses provided do not
consider the surcharge load imposed on excavated slopes by these stockpiles. The DBMS will require
evaluation.of surcharge loads for establishment of setbacks.
4. Shear strength parameters and stability analyses:
For more than a decade, the DRMS has employed a standard set of shear strength parameters for analysis
of typical sand and gravel deposits overlying weathered shale or claystone. A 2003 memo describing the
employment of these parameters is enclosed. Unless the Applicant chooses to conduct shear strength
testing of the onsite materials, the DRMS will require an analysis using the standard parameters to
establish appropriate setbacks. If the Applicant decides to conduct shear strength testing, the DRMS
should be consulted on appropriate test methods.
Office of Office of
Mined Land Reclamation Denver • Grand Junction 9 Durango Active and Inactive Mines