REV15956

• Permit No: C1980007
• IBM Index Class Name: Revision
• Doc Date: 7/6/2004
• Doc Name: Adequacy Review Letter
• From: DMG
• To: Mountain Coal Company
• Type & Sequence: PR10
• Media Type: D
• Archive: No

Permit Revision Adequacy
July 6, 2004
Page 12 of l8
much of the SOD, which is extremely critical with regard to potential impacts. Please correct
this important information.
93. Exhibit 60B, conclusions section, concludes that no cracks area predicted in the Dry Fork
alluvium because no cracks occurred in the alluvium in Apache Rocks. Please identify the
subsidence traverses located in any alluvium or alluvial valleys in Apache Rocks.
94. Please explain how subsidence observations from B-seam mining in areas of 1000-2000 feet of
overburden modify or temper conclusions regarding E-seam mining of 14 feet of coal in azeas
of 400-500 feet of overburden. Would the expected subsidence impacts be of greater or lesser
magnitude than the B-seam scenario?
95. In Exhibit SSA, page 10, the report states "These sediment yields are not expected to change by
mare than S% due to any change in hydraulic characteristics resulting from the increase in
slope as identified in Table 4." Is that an increase or decrease of 5%?
96. Exhibit SSA states "Monitoring of any channel morphology and geometry changes will allow
for site-specific prescriptive mitigation as deemed necessary" What are these prescriptive
mitigation measures?
97. Conclusion #2 in Exhibit 60B says predicted vertical displacement, tilt, and horizontal strain
predicted for the SOD area are likely to be conservative values (Le. greater than what will
actually occur). Yet in the same report, Figure 6, observed maximum subsidence over panels
1NW, 2NW, and 3NW was rg_eater than predicted in two out of three panels, contradicting
conclusion #2. Please explain and correct as necessary.
98. The DMG would not concur with conclusion #3 of Exhibit 60B. Based on mining to-date at
the West Elk mine, subsidence of a perennial stream and its associated alluvium has occurred
only in extremely limited areas due to B-seam mining with relatively thick overburden. Mining
of 14 feet of the E-seam coal in the northwest comer of section 33, T13S, R90W along the Dry
Fork is predicted to result in 6-I 1 feet of subsidence along the Dry Fork alluvium in azeas of
400-500 feet of overburden. This location will also bound un-mined coal, where maximum
perpetual tension could result in massive, long-term cracks in and azound the alluvium.
Relatively few studies have measured the hydrologic impact from longwall undermining.
However, one important study, Water Resources Investigations Report 95-4025, Hydrology of
the North Fork of the Right Fork of Miller Creek, Carbon Count Utah, Before, During, and
After Underground Coal Mining, 1995 found that subsidence in 300-500 feet of overburden
caused the stream to enter a fracture, drying up the stream bed below. Water quality was also
dramatically impacted. Temporary loss of stream flow is also documented in Colorado (Foidel
Creek mine). The potential for significant impacts to the Dry Fork above Minnesota Reservoir
above Panels E2 and E3 cannot be understated. Please reconsider conclusion #3.
99. Regarding conclusion #4 of Exhibit 60B, while the DMG agrees that visual evidence of
cracking in unconsolidated material (like alluvium) is rare, fracturing of bedrock immediately
below the alluvium has been confirmed in numerous cases. Fracturing of the underlying
bedrock would almost certainly result in leakage of the saturated alluvial aquifer and possibly