PERMFILE52001

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 6/2/2006
• Section_Exhibit Name: Exhibit 60B Subsidence Evaluation for the South of Divide Mining Area
• Media Type: D
• Archive: No

Suhsidence Evaluation For
Exhibd 608 South ~ Divide Mining Area Page 30
• Floor heaving, pillaz punching (the pillaz punches into the floor and roof rocks), and squeezing
(also Imown as plastic flowage, see Duntvd 1976, p. 36) are the only expected deformations in
the immediate mine floor, which commonly consists of impure coal, shale, sandstone, and
claystone. Deformation in the floors of the chain pillars is expected to occur after the longwall
panel is mined and the pillars begin to yield.
13.0 POSSIBLE SUBSIDENCE CONSEQUENCES
Predicted subsidence impacts for the Sotrth of Divide mining area has been described in detail
above- The greatest surface impacts are expected to occur along the precipitous slopes and cliffs
that flank Minnesota Creek, Lick Creek, and other tributaries. Though unli7cely, the worst
possible consequences foreseen are that cracks could locally form and be as much as 25 to 50
feet deep above chain pillars and bamer pillars in bedrock on the precipitous slopes, ridges,
and/or cliffs that flank Minnesota Creek, Lick Creek, and other tributaries, and may locally
accelerate the naturally-occumng rockfall and landslide process.
Some cracks are expected occur on the Dry Fork access road, however, in the area neaz the
confluence of Deer Creek and Dry Fork. Maximum vertical displacement ranging from 8.4 to
11,2 feet, tilt from 1.3 to 6 percent, and horizontal strain from 0.7 to 4.2 percent are projected in
the Dry Fork valley above the western limits of longwall panels E2 and E3.
Based on subsidence observations by the author (as discussed in Section 5.3.2), no cracks are
expected to occur in either the alluvium in the Dry Fork and Lick Creek drainages or stock
watering ponds and drainage diversion ditches. In addition, no cracks are predicted to occur in
colluvium more than about ten feet thick. The monitoring suggested in Section 113 will
compare results expected by the authoy and actual field results.
14.0 POTENTIAL IMPACTS FROM LOCAL SEISMIC ACTMTY
Earth tremors have been recorded or felt by local residents in the Somerset area since the eazly
1960s. The tremors commonly are the result of coalmine bumps and rock bursts, which are
spontaneous releases of strain energy in highly stressed coal and rock. In the Somerset Mine
area before closure, the bumps and rack bursa were common in room-and-pillaz mining areas
where stresses concentrated within isolated pillars and blocks of coal (called bump blocks).
Earth tremors have continued sporadically in the Somerset Mine area since the mine was closed
in the 1980s.
Tremors generated by bumps and rock bursts in the Somerset Mine area attain magnitudes that
have shaken structures in the West Elk Mine area and have been felt sometimes by West Elk
Mine personnel. These local tremors may affect, to a minor degree, underground workings,
landslide or potential rockfall areas, particularly during prolonged periods of increased
precipitation. It is noteworthy, however, that the Rulison nucleaz shot in 1969, which produced a
tremor with a Richter magnitude of 5.2 (the magnitude of energy released was many times
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