2014-10-10_PERMIT FILE - C1996083 ‎(8)‎

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 10/10/2014
• Section_Exhibit Name: Volume IIIA Exhibit 15 Subsidence Prediction
• Media Type: D
• Archive: No

The important factors and conditions that may influence the stability of the outcrop
barrier pillar are fairly well defined. The coal outcrop is well defined; it is further known that
at most locations along the outcrop, both seams are burnt out. At some locations, such as
the Bowie #2 Mine portal entries, little coal burn was present. The depth of the coal bum in
the horizontal direction is much less defined; we understand that based on the mining
experience in the area, the width of the burnt -out zone has been assumed to reach up to
300 feet. According to this assumption, the projected burn line, which coincides with the
southern mine limit, was estimated.
Mining limits in areas adjoining the outcrop barrier pillar are usually dictated by the
occurrence of oxidized (weathered) coal close to the outcrop. Such coal is of lower quality
and weaker than the good quality coal and it is not mined.
The presence of the burnt -out coal close to its outcrop brings about an additional
factor that is of importance for potential subsidence or stability problems in the vicinity of
the outcrop barrier pillar. The old coal fires, when reaching to significant depths into the
mountain, created a void space; the overburden lost its support and subsided. Distinct
fractures may have been developed above such subsidence features as described by
Dunrud (1976) in the Somerset - Paonia area.
It is evident that potential subsidence or stability problems in the vicinity of the
outcrop barrier pillars cannot be ruled out. Landslides of a significant extent have
developed close to the coal outcrop at the old Farmers Mine; it cannot be ruled out that
they are related to the collapse (crushing or sliding) of the outcrop barrier pillar as the
mining proceeded too close to the outcrop.
GEO -HYDRO Consulting, Inc. (1983) provides guidelines for a necessary width of
an outcrop barrier pillar in different geologic and hydrologic conditions. According to their
evaluation, a pillar width of some 50 feet should be sufficient in most conditions of the
Bowie #1 Mine to prevent crushing or sliding of the outcrop barrier pillar.
A barrier pillar of any width, assumed or otherwise, composed primarily of burnt
and /or oxidized coal may not be sufficient to minimize the effects of subsidence near the
outcrop. The Operator plans to leave one row of developed pillars (competent coal)
adjacent to the burnline (the point that poor quality coal is intercepted), and that this pillar
(100' width of competent coal) should prevent the potential crushing, sliding, orotherfailure
PR -14 -14- 03/14