1987-12-01_PERMIT FILE - C1981017 ‎(284)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Subsidence Study By Dr. Bruce Collins
• Section_Exhibit Name: Chapter IV Appendix IV-F-4
• Media Type: D
• Archive: No

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Formation member of the Mesaverde Group; the A-B coal zone,
the lowest mined in Coal Basin, essentially forms the base
of the Williams Fork. As has been discussed above, no
aquifers are thought to be present in this interval . With
two exceptions the sandstones present are lenticular stream
channel sands with limited individual bed lateral extent.
All of the sandstones are fairly tightly cemented and
commonly contain a clay matrix, further reducing ground-
water carrying capabilities. It should be noted that the
Mesaverde sandstones of this interval have been the target
of several "tight sand" natural gas stimulation tests in
the southern Piceance Creek basin in the last 15 years; none
of these tests have been spectacularly successful . In any
case, these sandstones outcrop or subcrop on the steep slopes
of the interior of Coal Basin. The steep slopes and cliffs
limit surface exposure to recharge, and recharge to any
potential aquifer is further reduced because the entire
sequence from the Rollins up is well-drained by Coal Creek
and its tributaries (the Rollins is everywhere above the
"floor" of the basin) , and the large amount of siltstone, mud-
stone and claystone in the sequence effectively seals the
sandstones from above. Therefore no damage to or diminuation
of the regional hydrologic system is anticipated.
Geologic conditions, i.e. general stratigraphy and structure,
in remaining unmined areas are essentially identical to those
• areas worked over the last 30 years . There is therefore no
reason to expect that future manifestations of subsidence or
subsidence-related phenomena will be any different than as
have been observed and measured to date. The only apparently
significant variable will be the actual aggregate thickness
of coal removed.
5 . Determination statement of the effects of subsidence , if
it did occur, on material damage or diminuation of reasonably
foreseeable use of structures or renewable resource lands.
Subsidence of the land surface over mined-out areas of the
Coal Basin mines has been detected by the subsidence monitoring
program initiated by MCR in 1981 . Maximum subsidence detected
to date is 2 .10 feet, at a point now apparently stable (MC-4) .
This amount of subsidence resulted from the extraction of at
least 8 feet of coal, and possibly as much as 16 feet (see
discussion in paragraph 3 above) . There are no visible sur-
face effects of subsidence, such as cracks, hummocked profiles
or subsidence-induced slumps or landslides in the large portion
of the area inspected for such features. There has been no
subsidence damage to the few structures, primarily mine ventil-
ation fans, or to power lines or light-use roads located over
mined-out areas. There are no known aquifers above the coal
beds being mined in the area, and renewable resource lands are
restricted to small livestock and wildlife summer grazing areas.
Neither MCR, White River National Forest (letter of 10/14/80)
nor Gunnison National Forest (letter of 9/1/80) plan on any