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Permit Revision Adequacy Comment Response November 30, 2004 Page 17 of 24 ~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. MCC Response: Revised text. 94. Please explain how subsidence observations from B-seam mining in azeas 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 scenazio? MCC Response: MCC addressed this in Exhibit 60B. 95. In Exhibit SSA, page 10, the report states "These sediment yields are not expected to change by more than 5% 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%? MCC Response: Both, depending on slope change. Text changed. 96. Exhibit SSA states "Monitoring of any channel morphology and geometry changes will allow for site -specific prescriptive mitigation as deemed necessary" What aze these prescriptive mitigation measures? MCC Response: This relates to comments 56 and 89, MCC has established study transects in the SOD drainages and proposed mitigation measures and monitoring. 97. Conclusion #2 in Exhibit 60B says predicted vertical displacement, tilt, and horizontal strain predicted for the SOD azea 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 reater than predicted in two out of three panels, contradicting conclusion #2. Please explain and correct as necessary. MCC Response: Figure 6 in 60B relates to calibration of the model and not prediction there is no contradiction. 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 pereruual stream and its associated alluvium has occurred only in extremely limited azeas due to B-seam mining with relatively thick overburden. Mining of 14 feet of the E-seam coal in the northwest corner of section 33, T13S, R90W along the Dry Fork is predicted to result in 6-11 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