2008-02-22_APPLICATION CORRESPONDENCE - C2008086 ‎(43)‎

• Permit No: C2008086
• IBM Index Class Name: Application Correspondence
• Doc Date: 2/22/2008
• Doc Name: PDEIS Appendix C Subsidence
• Media Type: D
• Archive: No

be decreased by as much as the maximum subsidence-induced tilt
change. See Figures 9B.
3. Horizontal tensile strain values generally greater than approximately 1
percent (10000 us) at 500-foot overburden depths and less also may
accelerate natural landslide movement or rockfall, particularly during
periods of high or increased precipitation. Figure 18. Ribside Tension
Cracks in Road Fill and Cliff Face, York Canyon Mine shows a
location where a sandstone cliff face failed after some of the shale
underlying a sandstone cliff face had been removed for the pioneer road
and then the headgate end of the longwall panel was mined past at
approximately 360 feet below but over 50 feet to the right of the cliff. The
estimated non-maximum tensile strain acting on the cliff face was about
0.5 percent (5000 us).
8.2 Mining Beneath Stream Courses
The only permanent stream courses indicated on the Garvey Canyon Quadrangle and
Howard Canyon Quadrangle for the Project Area are Big Salt Wash and East Salt
Creek. Big Salt Wash is the only perennial stream that overlies planned Red Cliff Mine
workings in the Cameo Seam. East Salt Creek does not cross over any part of the
Cameo Seam within the Existing Coal Lease or Coal Lease Application area. The
Cameo Seam outcrop crosses Big Salt Wash approximately 7,800 feet upstream from
the southern boundary of the Coal Lease Application area, as shown on Figure 13.
Overburden and Outcrop Map for the Project Area.
Within the Existing Coal Lease area, the Cameo Seam outcrop crosses the intermittent
stream course in Stove Canyon, Section 2, T. 8 S., R102 W. northwest of Big Salt Wash
and the intermittent stream courses in Munger Canyon and its southeast tributary,
Sections 22 and 27, S. 7 S., R. 102 W. These Cameo Seam outcrops are within the
Project Area.
Within the Coal Lease Application area the Cameo Seam outcrop crosses the
intermittent stream course in Buniger Canyon approximately 4,500 feet upstream from
where it meets the perennial stream in Big Salt Wash.
In order to mitigate potential subsidence impacts in the Coal Lease Application area and
the immediately adjacent north, east and south parts of the Project Area, it was
necessary to have a conceptual mining plan. The goals of the conceptual plan were to
maximize safety, then mitigate to the extent possible subsidence impacts and finally to
maximize resource recovery. The proposed portal is the anchor for the concept. The
conceptual plan that follows involves at least two sets of east-west mains driven off the
Big Salt Wash mains. A bleeder entry may well be necessary along the south boundary
of the Project Area. Either a bleeder entry or a third set of mains would probably be
required along the northern boundary of the Project Area.
It will be necessary to drive the main access entries approximately 5,000 feet N 45° E
from the planned Red Cliff Mine portal to where it will cross under the overlying
intermittent stream course in Stove Canyon at a depth of less than 200 feet., The main
entries will probably continue to a distance of approximately 9,000 feet where it will cross
beneath the intermittent stream course in Buniger Canyon at a depth of slightly less than
C-40
DBMS 332