2008-06-09_PERMIT FILE - C1980007 (5)

Home Browse Search

Summary MCC has analyzed the use of directional drilling to achieve degasification goals from sites outside the IRA and has noted the following: Based on preliminary plans these types of boreholes alone are inadequate for proper ventilation and efficient mine operations. These methods are already used by MCC where possible. Directionally Drill MDWs from Outside IRAs Directional drilling is limited by the thickness of overburden (or amount of rock) overlying the coal E seam. This limited thickness of overburden precludes the ability to drill exclusively from outside the IRA boundaries and hit the MDW targets needed in the ventilation plan. MCC expended a tremendous effort over athree- year period in an attempt to find a means to successfully accomplish degas drainage using the in-mine horizontal drilling system. These holes were drilled in the gateroads of the 14-17 panels and connected to a massive collection system to exhaust the gases from the mine. The conclusion of this effort was that the holes could not be drilled large enough, or stay open long enough, to allow safe mining of the coal (due to resulting high methane concentrations). They were simply very inefficient collectors of minimal quality gas, due to the limits of the drilling equipment in this application and the location of the gas-producing zones within the overlying strata. In MCC's previous experience in the B Seain approximately 13 percent of total mine methane was able to be vented horizontally (extracted from BLM analysis, 2007). Any attempt to degas the E seam via the horizontal drilling system would have the same issues and possibly more due to constraints of the overlying strata. Therefore, use of directional drilling opportunities has been used as much as possible, however because in places the overburden is not thick enough that directional drilling either from outside the IRA is practical or possible, therefore some of the operations must be placed in the IRA Helicopter Drilling of IRA Sites For safety reasons, in addition to, technical reasons regarding weight limits, this alternative was not carried forward for detailed analysis. Comparison of Alternatives This section provides a surmnary of the effects of implementing each alternative considered in detail (Table S-1). Information in the table is focused on activities and effects where different levels of effects or outputs can be distinguished quantitatively or qualitatively among alternatives. The analysis assumed that since coal could not be mined economically without the methane drainage, ventilation shaft and escapeway, the Alternative 1 would result in previously leased coal not being mined from the area affected. As discussed earlier in this chapter, the no action alternative would likely cause underground coal mining operations in the E seam to slow significantly or diminish entirely over time, due to the economic feasibility. Agency Preferred Alternative Alternative 2 -Proposed Action, including the design criteria is the Forest Service's preferred alternative. • • S-12 Deer Creek Ventilation Shaft and E Seam Methane Drainage Wells FEIS