2008-09-29_REVISION - C1981019 ‎(3)‎

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 9/29/2008
• Doc Name: Preliminary Adequacy Review
• From: DRMS
• To: Colowyo Coal Company
• Type & Sequence: TR74
• Email Name: JRS
• 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]
29 September 2008
Ms. Jennifer Sekulski
Colowyo Coal Company, LP
5731 State Highway 13
Meeker, CO 81641
Re: Colowyo Mine C-1981-019
Preliminary Adequacy Review - Technical Revision 74
Dear Ms. Sekulski:
COLORADO
D IV IS I ON OF
RECLAMATION
MINING
SAFETY
Bill Ritter, Jr.
Governor
Harris D. Sherman
Executive Director
Ronald W. Cattany
Division Director
Natural Resource Trustee
The Division has received your 10 July 2008 submittal of Technical Revision 74. The
revision was deemed complete on 18 July 2008. The Division has reviewed the Revision
and has the following adequacy questions.
West Taylor Pond
Figure IC-3
1) Four separate samples of "borrow" material were collected, and their physical
properties were analyzed in the laboratory. None of the samples met the
qualifications described in the originally-approved design; the Plasticity Index of
each fell short of that required to be classified as either CL or CH. In other
words, the fine-grained soils readily available consisted mainly of silt (which is
susceptible to "piping") rather than clay (which is plastic and binds together well).
The Acceptable Fill Materials note on the drawing was subsequently amended to
allow the field engineer to approve the use of other materials, following
appropriate laboratory testing. Given the lack of availability of more desirable
borrow material, this change is understandable.
2) Silty material is not normally desirable for the construction of earthen dam
structures. Because of this fact, a drainage filter mat was incorporated into the
design. The Division agrees with the decision to add this feature to reduce the
potential for a piping-related failure to occur.
Office of Office of
Mined Land Reclamation Denver - Grand Junction - Durango Active and Inactive Mines