PERMFILE41947

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 4/8/2005
• Section_Exhibit Name: 2.05 Operation and Reclamation Part 2
• Media Type: D
• Archive: Yes

West Elk Mine
I. Both Mr. Rogers and Mr. Hynes stated that, if the expansive shales and claystones of the
Mesaverde Formation in the subsurface were not at their highest attainable water saturation, the
addition of water in a subsidence crack would produce additional swell. More importantly, the
introduction of waters will increase the plasticity index of the shales or claystones. The higher the
plasticity index of a shale or claystone, the more easily it deforms: under the overburden pressure
assisting in crack closure. To put it simply, "the wetter a mud ball gets, the easier it is to mold."
WWE agrees with this analysis because overburden materials within the Mesaverde Formation
contain numerous shale layers and lenses which tend to undeigo plastic deformation under
compression. This seals fractures which may develop in response to subsidence. In addition,
siltation will assist in the filling of surface cracks which may develop, further reducing the potential
to transmit water downwazd.
Another important factor in minimizing the potential loss of surface water to the mine workings is
the depth of cover. D. Y. Dixon states in The Impacts of Three Longwall Coal Mines on
Streamflow in the Northern Appalachian Coal Fields (1989) that srreamflow showed fewer effects
of undermining with increased overburden thickness. Additionally,IK.L. Johnson (1992) found in a
study of two longwall mining sites in the northern Appalachian) coal field where the depth of
mining is 500-600 feet, that longwall mining beneath the two stream valleys did not lessen the
quantity or quality of shallow groundwater in the valleys, nor did it affect streamrlow.
Subsidence impacts on streams above two longwall mines studiedrecently in Utah help provide a
basis for further estimating impacts in the permit azea. The basic conclusion from the studies
. conducted at the Utah mines is that there has been no impact to date on stream base flow where the
~ overburden thickness is more than 500 to 600 feet. Some details are described below for two Utah
study azeas:
The area is located within U.S. Forest Service lands on the North Fork of Miller Creek at
Cyprus Plateau's Star Point Mine. Longwall mining panels were driven beneath this
perennial stream in overburden that ranges in thickness from 50 to 1,100 feet. Subsidence
cracks and diversion of streamflow were observed above the mining panels where the
overburden thickness was less than 300 feet to about 500 feet. However, no cracks or
reduction of stream base flow were observed where the overburden exceeded 500 feet
(LJSGS 1995).
2. This area is located within U.S. Forest Service land beneath a perennial stream neaz the
headwaters of Huntington Canyon. The Skyline Mine, recently started a third panel
beneath the stream at an average minimum depth of approximately 600 feet. The longwall
mining panel width is about 700 feet, which makes the depth roughly critical. The
subsidence factor reportedly ranges from about 0.5 to 0.8. Mining just recently began in
the third panel beneath the perennial stream, so all information should be considered
preliminary. No impact on stream base flow has been measured thus faz, however,
changes in the transverse stream channel profile and soine other hydrologic pazameters
have been observed (U.S. Forest Service 1995). '
• The E-Seam overburden thickness varies from approximately 4001 feet to 1,100 feet over the three
west longwall panels (i.e. the 12NW through 13aNW longwall panels) from which the E-Seam, as
2.05-154 November 2004 PRI