REP38979

• Permit No: C1996083
• IBM Index Class Name: Report
• Doc Date: 5/8/2006
• Doc Name: 2005 Bi-Annual Subsidence Report
• From: J.E. Stover & Associates Inc
• To: DMG
• Permit Index Doc Type: Subsidence Report
• Media Type: D
• Archive: No

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2. GEOLOGIC SETTING AND ROCK
QUALITY
The Somerset Coal Field is located on the
southeastern mazgin of the Piceance Basin, which
lies north of the Gunnison Uplifr, west of the Elk
Mountains, east of the Uncompahgre Uplift, and
south of the White River Uplifr. There are six
primary coal seams within the Somerset Coal Field,
ranging from 3 m (10 ft) thick on a single bench of
coal to over 7 m (20 ft) where one or more seams
merge [1]. An estimated 1.5 billion tons of
bituminous coal lie within the Somerset field. Coal
seams B, C, D, E, and F have been mined
historically in this basin. The coal seams contain a
very well developed cleat set oriented at N58° to
75°E [2].
The regional structural dip of the Mesa Verde
Formation is 3° to 5° to the north-northeast. The
predominant joint orientation of sedimentary rocks
is N68°E to N74°E in the basin, with secondary
jointing at N18°W to N35°W. Regional joint
patterns have been mapped by Carrol [1] and BRL
geologic staff.
During extraction of the D1 to D9 panels, BRL
geologic staff studied faulting using both surface
and underground observations. Both normal and
strike-slip faults have been encountered
underground but only one fault has surface
expression. The southern portion of the D6 panel is
traversed by a N80°-90°E left-lateral, strike-slip
fault system. The system is a complex array of
anastamosing fault planes of variable offsets.
A -2
Fig. 1. Mine layout, surface topography and location of subsidence monuments