2015-01-27_PERMIT FILE - C1996083A ‎(2)‎

• Permit No: C1996083A
• IBM Index Class Name: Permit File
• Doc Date: 1/27/2015
• Doc Name: pages 2.05-84 to 2.05-165
• Section_Exhibit Name: Volume I 2.05 Operation and Reclamation Plans Part 2
• Media Type: D
• Archive: Yes

2.05.6(6)
Longwall mining will be performed under West Terror Creek. No limited
extraction zone will be established under West Terror Creek. However,
longwall panels will be oriented approximately parallel with the creek thus
reducing the number and severity of transitions from subsidence to non -
subsidence zones (WWE 2013).
WWE conducted an analysis of potential subsidence impacts on the West
Fork of Terror Creek aquatic life and water supply due to potential mining of
the LBA tract (WWE, 2013). Mining would be expected to result in a
maximum subsidence of about 5.7 feet at the center, near the eastern edge,
of the longwall panel with the smallest overburden thickness. This location is
approximately 300 feet south of the West Fork of Terror Creek channel.
Based on existing topography and geologic modeling, a maximum estimated
5.1 feet of subsidence along the West Fork of Terror Creek channel would be
expected to create no more than a 1.5 percent channel slope change.
Because the LBA tract generally consists of steep terrain (often in excess of
25 percent slopes), the expected change in slopes is expected to be mostly,
if not completely, imperceptible without the aid of survey equipment. A
change of 2 percent within the average channel slope of 5.5 percent could
lead to an increase in the size of particles transported from 500 mm to 650
mm (WWE, 2013a). However, while some larger material would be mobilized
following channel slope increase induced by subsidence, the overall stability
of the largest particles should not be significantly compromised as a result of
the slope change (WWE, 2013a). Other subsidence related impacts, such as
surface cracking or water loss would not be expected to the degree that they
would negatively impact the quality of the aquatic habitat of the LBA tract.
Based on this analysis, adverse impacts to aquatic life would not be expected
as a result of potential subsidence within the LBA tract. WWE found that the
wetted perimeter of the West Fork of Terror Creek is not expected to change
noticeably following subsidence, based on the magnitude of slope changes
(WWE, 2013a). (Final Environmental Assessment DOI-BLM-CO-S050-2013-
0010 EA)
The above discussion by WWE is predominantly targeted to the aquatic life.
The change in slope would possibly increase the size of particles transported
from 500mm to 650 mm. Since the Terror Ditch is located approximately 1.6
miles blow the confluence of West Terror Creek and Terror Creek, additional
particles transported in West Terror Creek would have sufficient time to settle
prior to reaching Terror Ditch.
PR -14 2.05-164- 06/14