REV07196

• Permit No: C1980007
• IBM Index Class Name: Revision
• Doc Date: 2/4/1994
• Doc Name: TR 67 WEST ELK MINE PN C-80-007
• From: DMG
• To: CHRISTINE JOHNSTON
• Type & Sequence: TR67
• Media Type: D
• Archive: No

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STATE OF COLC~~~v~
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources .~~°F comer
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1313 Sherman Sr., Room 215 • ~~
Denver, CO 80203
Phone: [phone] ~ re~b ~
FAX: [phone] Roy Romer
Governor
Michael B. Long
To: Christine Johnston, Environmental Protection Specialist Division Director
From: Bruce Stover, Technical Support ~ C~ ~ i
Date: February 4, 1994 v `W~
Re: C-80-007, West Elk Proposed Storage Bench, TR 67
I have reviewed the materials you gave me pertaining to the proposed storage bench at the West
Elk Mine including a review of previous geotechnical reports for this mine site contained in
Exhibit 14 of the Permit. The Bench is to be constructed on the east side of the landslide area
as identified in Exhibit 14 reports. Although the bench is not situated within the area of study
of these landslide investigations, the drilling data indicates that the materials present are similar
in nature to those encountered in the landslide area immediately adjacent to the proposed
bench location. It is clear to me that the bench will be constructed in a similar geologic setting
to the main portal area, (colluvial slope failure and landslide deposits), except that the thickness
of the surficial colluvial deposits thins more rapidly upslope.
Factors of safety calculated for some sections of the proposed bench are right at the minimum
1.3 requirement, however, groundwater was not factored into these calculations, as water was
not encountered during drilling in August 1993. I believe this is a serious over sight affecting
long term stability of the proposed bench, and slope areas adjacent to it. Referring to the
geotechnical reports in Exhibit 14, Geotechnical Design Studies...Geo-Hydro Consulting Job No.
1015-004, Section 2.2 indicates that groundwater is often a seasonal condition at this site, and
that .."it has to be assumed that a complete saturation of the area can occasionally develop.:'
In section 3.1, this same report also warns, "..sliding would be triggered in the future when
unsupported cuts are excavated, or fills placed on steep slopes which are frequent in the
landslide area. These cuts or fills or other structures might be temporarily stable during a dry
season such as fall or winter, but they would become unstable during the spring season when
the combination of snow melt and rain apparently causes the saturation of certain areas:' The
reports contain many other references and recommendations pertaining to groundwater concerns
at this mine site.
Based on the hydrologic descriptions and general design approach recommendations contained
in Exhibit 14 geotechnical reports, I believe it is a mistake to design the proposed storage bench
without taking seasonal ground water conditions into account. Addition of water to the
proposed bench design calculations would likely put factors of safety below the required 1.3
minimum.