2022-09-29_PERMIT FILE - C1980007 (2)

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West Elk Mine wells 23-H-1 (B Seam), 23-H-3 (F Seam), and 23-H-4 (Barren Member). Water depths in the other three wells are at various levels, typically 100 to 200 feet above the completion interval. These data indicate the erratic nature of groundwater occurrence and the lack of interconnected water-bearing zones in the Mesaverde Formation. We1196-27-1 was completed in the fall of 1996. Baseline data for this well has been collected and is available in the 1997 and subsequent Annual Hydrology Reports. In 2003, three additional E Seam monitoring wells were constructed. These include Sec 3 E Seam Well, SOM-3-E, and 1-11-1-E which were constructed to provide baseline monitoring data. Conceptually, it is useful to visualize the following subsurface disturbance pattern for two-seam mining as illustrated in Figure 21. In this case, the B and E Seam are being mined. The B Seam is typically 1,000 feet to 1,200 feet under the ground surface in the Apache Rocks mining azea while the E Seam is typically at a depth of 800 to 1,000 feet. This indicates that the typical sepazation distance between the B and E Seam is 200 feet. Consequently, as the E Seam is mined, a caved zone 30 feet above the top of the seam will develop, along with a fractured zone extending up another 220 feet. This will place the combined caved/fractured zone up to 250 feet above the E Seam. Following E Seam mining, the B Seam will be mined. A total thickness of subsurface disturbance of approximately 450 feet can be calculated by adding the height of caved/fractured zone above the E Seam to the interburden distance between the B Seam and E Seam. The interburden distance was used instead of the caved/fractured zone above the B Seam, since the caved/fractured zone above the B Seam overlaps with the caved/fracture zone above the E Seam. Any groundwater within this 450-foot thickness may be disrupted and if such groundwater feeds springs/seeps, the springs/seeps aze likely to be affected, also. With respect to surface flow impacts, however, the minimum separation thickness between the top of the E Seam fractured zone and the ground surface is 150 feet, which means that surface flows (including springs) aze insulated from the caved and fractured zones by a minimum of 150 feet. Based on the available data, experience in the F and B Seams, and general knowledge of the Mesaverde Formation, mining in the E Seam is not expected to have significant impacts on the groundwater systems within the permit azea. Inter-relationships Between Groundwater and Snrinps The probable hydrologic consequences of B and E Seam mining and the expected subsidence effects on springs was previously discussed in Section 2.05.6. As discussed in that section, springs which are supplied by water-bearing bedrock units are at greater risk of relocation or dry-up as a consequence of longwall mining if: (1) The source bedrock unit is within the combined subsidence caved and fractured zone (approximately 270 feet above the B or E Seam mine workings, based on a conservative estimate by Mr. Dunrud), or (2) The bedrock unit from which a spring discharge is within approximately 100 feet of the surface and continuous across a chain or bamer pillaz (100 feet is a conservative projection by Mr. Dunrud of the maximum depth of surface cracks). 2.05-276 Revised June 2005 PRIG; Rev. March 1006; Rev. May 2006 PRIG