2008-04-22_PERMIT FILE - C1981017 ‎(15)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 4/22/2008
• Section_Exhibit Name: Chapter II-B Operation Plan - Permit Area
• Media Type: D
• Archive: No

Chapter II
Engineering studies of the site had concluded that it was geotechnically sound
(APP. II-B-3)
The character and physical properties of the rock tunnel waste were studied in detail by
Lincoln DeVore in 1979. Lincoln DeVore also performed the required stability analyses
and recommended appropriate construction procedures for the rock waste disposal
facility.
The studies indicated that the rock waste comprises a fairly good quality rockfill with a
minor amount of fines. According to the Unified Classification System, it could probably
be classified as a silty gravel (GM) or possibly as a poorly graded gravel-sand mixture
with little fines (GO).
Lincoln DeVore performed stability analyses of a slope not exceeding 60 feet in height.
The analyzed slope had two ten foot wide benches included. The slope between the
benches was 2(H):1(V). Other, flatter slopes were analyzed as well. As can be
expected, the factors of safety were reasonably high. A minimum factor of safety was
found to be equal to 3.5.
Based on the results of these analyses, Lincoln DeVore recommended to compact the
outer shell of the waste pile to 90% of Maximum Proctor Density. They also
recommended to place the waste in lifts not to exceed 12 inches loose thickness.
Material located beyond the outer shell of the pile was recommended to be spread in
lifts not exceeding two feet in thickness. No compaction was recommended for this
• zone of the facility.
Prior to disturbance of this area, topsoil and B horizon material were salvaged,
stockpiled, and revegetated.
Mid-Continent trucked the tunnel spoil material to the disposal area, then spread and
compacted it according to the Lincoln DeVore recommendations. Further
recommendations of Geo-Hydro in 1984 were also followed.
Mid-Continent hired Geo-Hydro Consulting, Inc. (Geo-Hydro) to determine whether
construction methods for the rock tunnel disposal site met applicable design criteria,
and recommend any necessary changes to construction methods. The Geo-Hydro
report was submitted in 1984, and is contained in (App. II-B-3).M
Geo-Hydro reviewed all available material related to the construction of the rock tunnel
waste disposal facility, reviewed the stability analyses, construction procedures which
had been recommended in the pertinent reports, and the applicable regulations of the
state.
*W.A. Wahler & Associates: Mid-Continent Coal and Coke Company, Laboratory
Test Results (1977); Morrison-Knudsen Company: Refuse Disposal Study (1977);
Lincoln DeVore: Slope Stability Analysis, Mid-Continent Tunnel Project (1979).
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