ENFORCE37234

• Permit No: C1981019
• IBM Index Class Name: Enforcement
• Doc Date: 5/25/1995
• Doc Name: NOV C-90-005 COLOWYO COAL MINE C-81-019
• From: DMG
• To: COLOWYO COAL CO
• Violation No.: CV1995005
• Media Type: D
• Archive: No

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STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Depanmenl 01 Natural Resources
1313 Sherman 51., Room 215
Denver, ColoraAo 80?03
Phone [phone]
FAX: [phone]
May 25, 1995
Mr. Jim Kiger
Senior Environmental Engineer
Colowyo Coal Company
5731 State Highway 13
Meeker, CO 81641
RE: NOV C-90-005
Colowyo Coal Mine (C-81-019)
Dear Mr. Kiger:
I~~~
DEPARTMENT OF
NATURAL
RESOURCES
Roy Romer
Governor
lames 5. LochheaA
Executive Director
Michael e. Long
Dinsion Director
Following review of aerial and on-the-ground observations of the West Pit area during
recent inspections, the Division has determined that a modifcation of the abatement
measures for NOV C-90-005 is warranted. We feel additional analysis and design work for
the hillside next to the West Pit pond and fill is warranted because instability within the
disturbed portion of the hill has continued to express itself despite previous efforts at
control. The modified abatement measures are necessary to address the stability of the
pond and the slope above the pond which has exhibited increasing signs of instability during
recent weeks. The NOV modification is enclosed, and additional information is provided
in this letter. The modification will essentially allow the NOV to be terminated upon
completion of analysis and design work by Colowyo, and commitments to implement any
necessary repairs in a timely manner.
The Division is requiring submittal and approval of a technical revision to address the
stability of the slope near the pond. The adequacy of the pond's capacity should be
reevaluated after any remedial measures have been completed. In order to assess the
stability of the slope, a triaxial shear analysis of representative material on the slope and/or
pond in-slopes would be appropriate. This information, in conjunction with identification
of the phreatic surface in the slope, and identification of slip surfaces will facilitate the
design of appropriate remedial measures for stabilizing the slope and pond. The design
documentation should include an appropriate slope stability analysis. Piezometers and slope
movement monuments should be installed to verify conditions following slope repair.
Installation of the piezometers prior to remedial efforts would be most beneficial since the
effects of repair work on the phreatic surface could actually be verified.