2011-09-26_PERMIT FILE - C1981012 ‎(24)‎

• Permit No: C1981012
• IBM Index Class Name: Permit File
• Doc Date: 9/26/2011
• Section_Exhibit Name: EXHIBIT 08 HYDROLOGY AND GEOLOGY INFORMATION
• Media Type: D
• Archive: No

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Subsidence over the mined panels would be manifested at the surface as gentle, almost imperceptible
troughs with shallow tension cracks at the edges and in other areas of local extension. The maximum
potential subsidence associated with mining adjacent panels in either the Allen or Apache would be 2.6
feet. Subsidence would be most likely to occur in areas with thin overburden. The calculated subsidence
over one panel at a depth of 1,200 feet is 2.0 feet. Retreat mining and subsidence below the Purgatory
River is not planned, and a subsidence buffer zone will be left in place around the alluvial valley floor.
Published research indicates that subsidence from mining has predictable effects on surface water and
groundwater hydrology. Kendorski (1993), recognized five zones above subsided panels that have
different hydraulic responses and characteristics. These zones are summarized in Table 17.
Table 17. Hydrologic Effects of Subsidence above Mining Panels
Zone
Probable Hydrologic Consequences New Elk Mine
Extent
26
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Increased Transmissivitv
Zone of complete stratigraphic disruption. Extends two to eight times the mining
Caved Zone
Table 16. Predicted Subsidence for Mining in the Allen and Apache Coal Seams
height above the seam. Roof strata collapse into the opening and form rotated blocks
Maximum Maximum Horizontal Strain
Maximum
Maximum Curvature
mined seam
Scenario Subsidence millistrain
Slope
1 /ft
ft Tensile Compressive
%
Positive Negative
From top of caved
Case 1 - 450 feet of overburden
Potential for localized
zone to a maximum of
One mined panel
2.6
6.89
6.88
1 1.29
0.99
0.99
Two mined panels
2.6
1 6.88
6.89
1.29
0.99
0.99
Case 2 - 1,200 feet of overburden
Zone of beam deformation in which strata sag but do not form vertically connected
One mined panel
2.0
2.55
4.91
0.47
0.26
0.14
transmission of water into underlying zones. Generally extends from about 24 to 60
Two mined panels
2.6
2.58
2.59
0.49
0.14
0.14
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Subsidence over the mined panels would be manifested at the surface as gentle, almost imperceptible
troughs with shallow tension cracks at the edges and in other areas of local extension. The maximum
potential subsidence associated with mining adjacent panels in either the Allen or Apache would be 2.6
feet. Subsidence would be most likely to occur in areas with thin overburden. The calculated subsidence
over one panel at a depth of 1,200 feet is 2.0 feet. Retreat mining and subsidence below the Purgatory
River is not planned, and a subsidence buffer zone will be left in place around the alluvial valley floor.
Published research indicates that subsidence from mining has predictable effects on surface water and
groundwater hydrology. Kendorski (1993), recognized five zones above subsided panels that have
different hydraulic responses and characteristics. These zones are summarized in Table 17.
Table 17. Hydrologic Effects of Subsidence above Mining Panels
Zone
Effect
Extent
Characteristics
Increased Transmissivitv
Zone of complete stratigraphic disruption. Extends two to eight times the mining
Caved Zone
8 to 52 feet above
height above the seam. Roof strata collapse into the opening and form rotated blocks
intersected groundwater
quickly drained into mine
mined seam
with increased volume that limits the upward progression of caving. Groundwater
intersected by the caved zone is quickly drained into the mine workings.
Increased Transmissivity
From top of caved
Zone of vertically transmissive fractures without rotation. Bedding retains original
Potential for localized
zone to a maximum of
attitude and does not fall or detach. Fracture density and permeability increase
Fractured Zone
interconnection of
about 195 feet above
downward. The combined height of the fractured and caved zones can be 20 to 30
groundwater in the Allen,
times the mining height. Increased vertical and horizontal permeability allow for
Apache and Maxwell seams
mined seam
drainage of intersected water into the mine workings.
Zone of beam deformation in which strata sag but do not form vertically connected
Increased Storage
from top fractured
fractures. Bed dilation increases groundwater storage but does not allow for vertical
Potential for temporary
zone to a maximum of
m
transmission of water into underlying zones. Generally extends from about 24 to 60
Dilated Zone
decrease in water levels as
abou t 390 feet above
times the mining height above the seam. Wells and surface water intersected by the
the additional storage
dilated zone will experience temporary reductions in level /volume as water goes into
volume is filled.
mined seam
storage. Water levels typically recover to pre- mining levels after the increased
storage volume has been filled.
No Chanee
top of the dilated zone
Zone of no significant effect on transmissivity and storage. Strata are affected by
Continuous
Constrained
Potential for Hydrologic
to 50 feet below
subsidence but are not sufficiently deformed or strained to dilate and significantly
Zone
Zone
impacts is minimized.
ground surface
increase storage. Overall extensile strains remain less than 0.1%, the point at which
rock masses are not sufficiently disrupted to increase permeability.
17
Surface
Increased Transmissivity
Surface zone with shallow tension fractures caused by subsidence. Fractures
Potential for localized,
Fracture
0 to 50 feet below
generally extend less than 50 feet below ground surface and are spatially related to
Zone
short- duration changes in
ground surface
panel /trough edges and areas of local extension. Changes in hydraulic regimes are
groundwater levels.
short lived because fractures are localized, shallow, and quickly filled by sediment.
Note: Zone thickness are calculated based on a mining height of 6.5 feet.
4164A.110130 Whetstone Associates
PR 02 Exhibit 8(4) Page 147 Revised 1/31/11