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2022-09-29_PERMIT FILE - C1980007 (2)
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2022-09-29_PERMIT FILE - C1980007 (2)
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Last modified
10/6/2022 2:39:13 PM
Creation date
10/6/2022 2:29:35 PM
Metadata
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Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
Permit File
Doc Date
9/29/2022
Doc Name
pg 2.05-200 to 2.05-300
Section_Exhibit Name
2.05.6 Mitigation of Surface Coal Mining Operation Impacts Part 2
Media Type
D
Archive
No
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West Elk Mine <br />• Cumulatively, the estimated "time to £ilP' the entire West Elk Mine workings in all three coal <br />seams is approximately 290 years (maximum fill time) based on current inflow observations <br />and those additional inflow estimates assumed for the South of Divide mining area. <br />F Seam Impacts on Groundwater <br />Until summer 1991, mining at West Elk Mine was by room-and-pillar 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 azeas 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 azeas of low cover near 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 areas, 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 azeas 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 near-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 />comparable 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 Mesauerde 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 pillaz 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 />• <br />1.03-164 Revised June 1005 PRIO; Rev. March 2006; Rev May 2006 PRl0 <br />
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