2008-03-21_PERMIT FILE - C1980007A (4)

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Vest Elk Mine is Lower Coal Member (Mesa Verde Formation) The Lower Coal Member contains approximately 300 feet of interbedded shales, fine-to-medium- grained sandstones and relatively persistent coal seams. The Lower Coal Member of the Mesaverde Formation includes the A, B, and C coal seams. This member is generally considered to be that portion of the Mesaverde Formation between the Rollins Sandstone and the D-Seam, and includes the Upper and Lower Marine Sandstones. These sandstone units are not a single, persistent bed but actually several thick lenticular sandstones occurring at progressively lower stratigraphic horizons. The Lower Coal Member contains some sandstone units that locally may produce water. This is supported by observations within the B Seam mine workings, which show that the average annual inflow to the mine, prior to 1996, is approximately 12 gpm. While this observation continues to hold true for sandstone units near the B Seam, development mining has encountered faults which can contain significant quantities of water (see Permeability and Factors Influencing Permeability later in this section). Information from mines operating in the Lower Coal Member (i.e., Somerset and Bear No. 1 and No. 2 Mules) demonstrates that there is a lack of water in this member. Even after the onset of subsidence during retreat mining, there was no reported increased flow of groundwater fiom this formation into the Somerset Mine, even though it is located down-dip of the North Fork (U.S. Steel Somerset Mine MRP, Section 2.04-7, Hydrology Description). Of specific importance in this Lower Coal Member of the Mesaverde Formation is the B Seam coal itself. Five groundwater monitoring wells currently monitor the B Seam (SOM-129-H, RAV- 4b, So.W-1, 01-11-1B, and, most recently, SOM-3B). Monitoring well 01-11-1B was constructed in 2001 down-dip of Box Canyon Panel 18 while monitoring well SOM-3B was constructed in 2003 to begin assessing B Seam conditions prior to mining in the South of Divide permit revision area. Well SOM-23-H-1 was constructed in 1974 and monitoring was reinitiated in 2005 to assess B-Seam conditions prior to inning in the South of Divide pen-nit revision area. However, the well casing in this well has been damaged and monitoring will not be continued. Between April and June 2002, the well casing in So. W-1 collapsed making it no longer functional as a monitoring well. SOM C-72-H was removed from the monitoring program in 1999, because the bottom of the well was affected by mining in the B Seam. SOM C-72-H is actually completed in the sandstone unit irmnediately above the B Seam. A pumping test analysis was conducted on well SOM-23-H-1, also completed into the B Seam. However, the very low flow rate (estimated at 1 gpm) was insufficient to be able to quantify any hydrogeologic parameters and therefore no meaningful conclusions could be drawn from this analysis. SOM-23-H-1 was removed from the monitoring program in June 1998. Slug-test analyses were performed on B Seam monitoring wells SOM-127-H (now sealed) and SOM C-72-H. Permeability measurements from these analyses (presented in Table 5) indicate that the in-situ values are less than 10 feet per year (1 x 10-5 cm/sec). This value was also confirmed in core plug analysis of samples between the A and B Seam coals by Mayo and 2.04-65 Revised June 2005 PRIG, Marcia 2006; Rev. April 2006 PRIO, Sep. 2007PR12