GENERAL52614

• Permit No: C1981044
• IBM Index Class Name: General Documents
• Doc Date: 4/24/1987
• Doc Name: Proposed Decision & Findings of Compliance for PR1
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

Spur and irrigation ditches within the proposed permit area. Renewable„
resource lands identified within the permit area include the alluvial valley
floors of the Big Bottom area, the Yampa River and the Williams Fork Rivers,'
the Yampa and Williams Fork Rivers themselves, and several bedrock aquifers.
B. Subsidence Survey and Subsidence Prediction
The amended permit application includes an analytical projection of worst-case
and probable consequences of subsidence within the permit area. Worst-case
predicted and maximum predicted (probable) subsidence projections are
presented on Table 79 of the amended permit application.
In compliance with the existing permit for the Eagle No. 5 and Eagle No, 9
Mines, Empire Energy Corporation has submitted semi-annual subsidence
monitoring reports for the mined areas. These survey subsidence monitoring
results allow Empire Energy Corporation to forward the following observations:
"Subsidence monitoring has been conducted above
full-extraction room-and-pillar panels in the Third East
area. The results of this monitoring indicated that for an
extraction height of from eight (8) to ten (i0) feet and an
approximate extraction ratio of 80 percent, the magnitude
of maximum subsidence was 4.8 feet. This represents
subsidence for a super-critical width:depth geometry. In
other words, the maximum subsidence that could occur, did
occur. In addition, there were some surface cracks
associated with this subsidence. The surface cracking
generally occurred above the barrier pillar ribsides: The'
maximum width of the cracks was one (1) foot: The vertical
offset across the cracks was less than one (1) foot. The
cracks tended to close up after about 24 months.
Subsidence monitoring has been conducted above the first
longwall panel of the No. 5 Mine. As of the time of this
Permit Revision submittal (August 1986), the latest survey
of the monitoring net was conducted in December, 1985. The
maximum observed subsidence was 6.11 feet for an extraction
height of ten (10) feet. The represents subsidence for a
range of width depth ratios of 0.75 to 1.2. The angle of
draw varied from less than D to a maximum of 15.5 degrees.
It should be noted that both of these values are less than
the maximum values predicted prior to mining. The
predicted maximums for subsidence and angle of draw were::
7.5 feet and 19 degrees respectively. There has been some
surface cracking associated with this subsidence. In
general, the cracks have tended to parallel the surface
topography (E7kens, 1986, Drawing No. 8519-lS - Annual
Subsidence Report): Because the surface cracks roughly;;
parallel the surface topography, they have tended to remain
open. It is anticipated that surface wash will close the
cracks within 12 to 24 months."
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