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West Elk Mine <br />Until summer 1991, mining at West Elk Mine was by room-and-pillaz methods within the F <br />Seam. Although no further F Seam mining is planned at West Elk Mine, valuable information <br />can be derived from the historic F Seam mining; consequently, this subject is addressed. <br />The F Seam mine inflow map in the Annual Hydrology Reports shows all areas within the F <br />Seam mine workings at which there were observed inflows between 1981 and the beginning of B <br />Seam longwall mining in July 1992. Areas in which noticeable dampness or water inflow had <br />been reported were limited to less than 5 percent of the total mine workings. Sustained inflows <br />were observed only in areas of low cover neaz the portal and the Sylvester Gulch fan. Most of <br />the low cover areas within the permit azea correspond to the fracture controlled drainages shown <br />on Map 24. <br />The portal and vent azeas, also used for entry access to the B Seam mine workings, receive <br />seasonal inflows from colluvial/landslide and alluvial materials during spring snowmelt. Initial <br />inflows in these areas were typically observed at three to five times the rate of steady or long- <br />term flow rates within the mine. With the exception of the neaz-surface azeas, noticeable inflows <br />to the mine workings were observed only under Lone Pine Gulch and the upper reaches of <br />Sylvester Gulch. These inflows aze somewhat seasonal and controlled mainly by fracturing and <br />shallower overburden. This relationship was exemplified by the absence of water inflow when <br />main entries (Jumbo North and B West Mains) were developed under the upper reaches of Gribble <br />Gulch. <br />Figure 24 shows the response of monitor well SOM 38-H-1 to mining in the F Seam. This well <br />represents one of several water level monitoring wells under which F Seam room-and-pillar mining <br />occurred. As can be observed in the Figure 24 hydrograph, a drop in groundwater level of <br />approximately 100 feet occurred over approximately a six month period starting in January 1987 <br />following retreat mining beneath the well. Groundwater levels subsequently recovered to elevations <br />compazable with pre-mining conditions. This decline and subsequent recovery suggests that caving <br />followed by stress redistribution and "healing" (closing of the fractures) occurred within <br />approximately three months following the sudden drop in water level. Monitor well SOM 38-H-1 is <br />completed in the Barren Member of the Mesaverde Formation approximately 500 feet above the F <br />Seam. This influence was observed at a greater height above the F Seam than that predicted for the <br />E and B Seam longwall mining, however, it is important to note that room and pillar mining creates <br />fractures that aze less uniform and less predictive than those from longwall mining. <br />B Seam Impacts on Groundwater <br />B Seam longwall mining operations began during Summer 1992 (see Map 52). Several water <br />level monitoring wells in the current B Seam longwall mining area have been used to observe <br />groundwater effects resulting from this mining method. These monitoring wells include SOM <br />38-H-1, SOM C-72-H, and SW-1 through SW-6 and JMB-12. <br />The 1NW Panel was the first panel mined using the longwall mining technique. Complete <br />mining of this panel took approximately nine months (i.e., July 24, 1992, to May 1, 1993). <br />Figure 24 shows the observed water levels in monitoring well SOM 38-H-1, including the <br />• <br />2.05-223 Revised November 1004 PRIG <br />