GENERAL51403

• Permit No: C1981020
• IBM Index Class Name: General Documents
• Doc Name: RECOMMENDATION FOR SALT CREEK MINING CO MUNGER CANYON MINE GARFIELD COUNTY COLO LEASE #C-0125515
• From: OSM
• To: JAMES R HARRIS
• Permit Index Doc Type: GENERAL CORRESPONDENCE
• Media Type: D
• Archive: No

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Geo-Nydro's report contains the statement; "If our recommendations are accepted,
the cuts will probably be stable for the Zifetime of the mine; sloughing will
have to be expected and maintenance of the road will be required." The applicant's
consultant has determined those cut slope gradients which should be stable
during the operational Zife of the mine. In other words, the consultant has
deduced what cut slope gradients for each characteristic soil or bedrock type
encountered will assure a cut slope with a static slope safety .`actor which
exceeds 1.0. The aaplicant's consultant did ccmplete a mathematical stability
analysis of the cut slopes or fill embankments proposed to accommodate the
enlarged haul road.
Rule 4.03.1(3)(d)(ix) requires that no haul road fill embankment exceed a slope
of 2:1 (horizontal to vertical), unless the applicant demonstrates that the
steeper proposed embankment will be stable. A11 fill embankments proposed
within the application are specified as having slopes of 2:1 and are, therefore,
in compliance with the permanent regulations.
Rule 4.03.1(3)(cl(i) requires that no haul road cut slope exceed a slope of Z.S:I
(horizontal to vertical) in unconsolidated materials or a slope of 1/4:1
(horizontal to vertical) in competent rock. Rule 4.03.1(3)(c)(i) does, however,
allow Far slopes in excess of the stated maximums. The rule states; "...except
that steeper slopes may be specifically authorized by the Division if geotechni.cal
analysis demonstrates that a minimum safety factor of _'.5 can be maintained or
if geotechnical analysis demonstrates that a safety factor Zess than 1.5 will not
result in significant environmental harm or harm to the public hea_'th and safety."
Close scrutiny of the apclicant's proposed alignment and grading of toe haul road
corridor has determined that the cut slopes proposed at various locations between
the design survey stations Iisted below exceed the aiicwed maximum slope gradients
for cut slopes constructed in unconsolidated ;naterials (see Figures 2.2-Io
through 2.2-3).
Station 72+70' through
Station 82+25' through
Station 85+75' through
Station 88+40' through
Station 95+00' through
Station 101+00' throug,
75+50'
83+60'
87+25'
95+00'
101+00'
~ Zoa+;o'
T,Se geological mapping included wi thin Exhibit 0, the report prepared by Geo-
~iydro Consultants, Inc. indicated that each of toe above-listed cut slopes will
be e:rcavated in materials which were mapped as unconsolidated soils. (See geo-
technical map, sheets 1, and 3, Exhibit 0 or t!:e application.) The applicant
proposes to excavate these soils to finish slopes or roughly 1:1 /horizontal to
vertical). Slope heights will reach 135 feet. Slopes which exceed o0 feet in
vertical .`,ei?ht are designed with a 15 foot wide intermediate terrace bench,
which mil! result in overall slope gradients berween ..'_:1 and 1.1:1 (horizontal
co vertical) for p4e a_`fected cut slopes.
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