2006-08-04_REVISION - M1978056

• Permit No: M1978056
• IBM Index Class Name: Revision
• Doc Date: 8/4/2006
• Doc Name: Stability Analysis Review
• From: DRMS rmw
• To: DRMS
• Type & Sequence: TR2
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman S[., Room 215
Denver, Colorado 80203
Phone: (303) 86(x3567
FAX: [phone]
Date: August 4, 2006
To: Tom Schreiner
Cc: Carl Mount (via a-ma
From: Rick Wenzel
COLORADO
DIVISION O F
MINERALS
GEOLOGY
EFCLAM ATION•NI NIN(.
FAFETY•SCIENCE
Bill Owens
Govemar
Russell Geolge
Executive Director
Ronald W. Cattany
Division Director
Natural Resource Trustee
RE: Durham Sand and Gravel Pit Slope Stability Analysis Review, Technical Revision
No. TR-2, Permit No. M-1978-056 C/ess: /~BV+Siu)y
As requested, I have reviewed the report prepared by CGRS, Inc. titled "Slope Stability Analysis,
Varra Gravel Operation -Durham Pit, Greeley, Colorado, CGRSNo. 1-135-9929" and dated May
17, 2006, which was submitted to the Division on May 31, 2006 by Varra Companies, Inc. The
purpose of the review was to verify that the operator has adequately demonstrated that the proposed
re-grading and reclamation of the existing flood control berm will not damage the existing
underground gas pipeline and that the modified embankment will have an adequate factor of safety
during and after a 100-year flood event.
The cross-section of the embankment where the gas line is located indicates that the maximum cut
along the existing berm will be approximately two feet, while the maximum fill will be
approximately one foot. Typically, gas lines are located between three and four feet below the
ground surface; therefore, cuts of two feet should not affect the existing gas line. However, the
Division recommends that the operator contact the Utility Notification Center of Colorado to locate
any underground utilities prior to beginning any excavation work. The proposed fills to be
constructed on the existing berm should have no effect on the buried gas line due to their minimal
height.
Review of the slope stability analyses provided in the CGRS report indicates that the modified berm
has river side factors of safety varying between 4.05 and 5.66 and pit side factors of safety varying
between 1.99 and 2.35. These factors of safety were determined for before, during, and after a 100-
year flood event using soil criteria based on both field and laboratory data.
Based on my review ofthe aforementioned report, the operator has adequately demonstrated that the
proposed re-grading and reclamation of the existing flood control berm will not damage the existing
underground gas line and that the modified embankment will have an adequate factor of safety
during and after a 100-year flood event.
Should you have any further questions regarding this issue, please feel free to contact me.
Office of Office of Colorado
Mined Land Reclamation .Active and Inactive Mines .Geological Survey