2008-10-24_REPORT - M2005071

• Permit No: M2005071
• IBM Index Class Name: REPORT
• Doc Date: 10/24/2008
• Doc Name: Vibration Monitoring Results
• From: DRMS-acs
• To: DRMS-sss
• Permit Index Doc Type: Blasting
• Email Name: ACS
• Media Type: D
• Archive: No

? ,PDIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
STATE OF COLORADO
DATE: October 24, 2008 c?
COLORADO
D IV IS I ON OF
RECLAMATION
MINING
SAFETY
Bill Ritter, Jr.
Governor
TO: Steve Shuey Harris D. Sherman
Executive Director
FROM: Allen Sorenson Ronald W. Catt
Division Director
or
Natural Resource Trustee
RE: Vibration Monitoring Results, Benson Brothers Red Shale Pit, Permit No. M-2005-071 I
As we discussed by telephone when the vibration monitoring reports for the Benson Brothers Red Shale Pit
were received in late August and early September, the data demonstrate that vibrations caused by activities in
the pit will not exacerbate rock fall along the cliffs located to the south. Seismographs set to trigger at
vibrations of 0.01 inches per second peak particle velocity were set up near the cliffs on July 15, 2008 and
were not activated by vibrations from heavy equipment and crushing operations in the pit. Vibrations
measured that day in the pit approximately twenty feet from a D9 CAT ripping in bedrock were 0.08 inches
per second. The closest dozer operations can occur to the cliffs under the terms of the permit is 340 feet. For
perspective, the vibrations measured twenty feet from the CAT are the types of vibration equivalents that
would occur in a home caused by people walking or jumping. Door slamming and nail driving cause much
higher vibration equivalences (see attachment no. 1). The thirty day vibration monitoring conducted at the site
in July and August 2008 indicates that no vibration from the pit exceeding the seismograph trigger level
occurred at the monitoring station located between the pit and the cliffs. There were vibrations recorded by
the seismograph on a daily basis from July 24 through August 15, 2008, but these vibrations were at 0802
hours each day and were clearly the result of instrument start up.
Although there is no increased threat of rock fall from operations in the pit, the following information must be
provided for Benson Brothers to fully comply with the terms of the permit.
1. Provide PreSeisTek Inc. certification that the seismographs used for the required monitoring conform
to standards recommended by the vibration section of the International Society of Explosives
Engineers and that the instruments were calibrated by the manufacturer in the 12 months prior to their
use at the site.
2. Provide the instrument trigger level setting for the seismograph used in the thirty day monitoring
program.
3. Provide clarification of the discrepancy contained in the following statement from the letter by Revey
Associates to Benson Brothers dated August 8, 2008. "In the recent testing at the Red Shale Quarry
site, the peak ground motion caused by the D9 Dozer, at a distance of 20 feet was 0.08 in/s. This value
is less that the peak predicted value of 0.011 in/s (0.0187(20)-0'178).
Attachment no. 2 is informational and comprises some of the research into equipment vibration and rock fall
gathered by the Division during initial consideration of the Red Shale Pit permit application.
attachment(s)
c•\acs files\Iyty Documents 4-19-06 thru\red shale vib mon review_d_o_c_
Office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive MineE