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West Elk Mine <br />Lower Coal Member (Mesaverde Formation) <br />The Lower Coal Member contains approximately 300 feet of interbedded shales, fine-to-medium- <br />grained sandstones and relatively persistent coal seams. The Lower Coal Member of the Mesaverde <br />Formation includes the A, B, and C coal seams. This member is generally considered to be that <br />portion of the Mesaverde Formation between the Rollins Sandstone and the D-Seam, and includes <br />the Upper and Lower Marine Sandstones. These sandstone units are not a single, persistent bed but <br />actually several thick lenticular sandstones occurring at progressively lower stratigraphic horizons. <br />The Lower Coal Member contains some sandstone units that locally may produce water. This is <br />supported by observations within the B Seam mine workings, which show that the average annual <br />inflow to the mine, prior to 1996, is approximately 12 gpm. While this observation continues to <br />hold true for sandstone units near the B Seam, development mining has encountered faults which <br />can contain significant quantities of water (see Permeability and Factors Influencing Permeability <br />later in this section). <br />Information from mines operating in the Lower Coal Member (i.e, Somerset and Bear No. 1 and <br />No. 2 Mines) demonstrates that there is a lack of water in this member. Even after the onset of <br />subsidence during retreat mining, there was no reported increased flow of groundwater from this <br />formation into the Somerset Mine, even though it is located down-dip of the North Fork (U.S. Steel <br />Somerset Mine MRP, Section 2.04-7, Hydrology Description). <br />Of specific importance in this Lower Coal Member of the Mesaverde Formation is the B Seam coal <br />itself. Five groundwater monitoring wells currently monitor the B Seam (SOM-129-H, RAV- <br />4b, So.W-1, O1-11-1B, and, most recently, SOM-3B). Monitoring well 01-11-1B was <br />constructed in 2001 down-dip of Box Canyon Panel 18 while monitoring well SOM-3B was <br />constructed in 2003 to begin assessing B Seam conditions prior to mining in the South of <br />Divide permit revision area. Between April and June 2002, the well casing in So. W-1 <br />collapsed making it no longer functional as a monitoring well. <br />SOM C-72-H was removed from the monitoring program in 1999, because the bottom of the well <br />was affected by mining in the B Seam. SOM C-72-H is actually completed in the sandstone unit <br />immediately above the B Seam. A pumping test analysis was conducted on well SOM-23-H-1, also <br />completed into the B Seam. However, the very low flow rate (estimated at 1 gpm) was insufficient <br />to be able to quantify any hydrogeologic parameters and therefore no meaningful conclusions could <br />be drawn from this analysis. SOM-23-H-1 was removed from the monitoring program in June <br />1998. <br />Slug-test analyses were performed on B Seam monitoring wells SOM-127-H (now sealed) and <br />SOM C-72-H. Permeability measurements from these analyses (presented in Table 5) indicate <br />that the in-situ values aze less than 10 feet per yeaz (1 x 10-5 cm/sec). This value was also <br />confirmed in core plug analysis of samples between the A and B Seam coals by Mayo and <br />Associates (1998). <br />U <br />2.04 -65 RevisedNavember 1004 PRt 0 <br />