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West Elk Mine <br />1. Caved Zone - As coal is extracted and a void is produced, the immediate roof rocks break <br />along bedding planes, joints, and fractures and fall to the mine floor. This is defined as the <br />"Caved Zone." Within this zone, existing fractures tend to open ("dilate") and many new <br />fractures are created. Therefore, this zone will be associated with a relatively high secondary <br />permeability and is directly tied to the highly permeable rubble zones in the workings. Any <br />groundwater present in the caved zone will drain into the mine immediately after caving <br />occurs. To date, no such observation of significant groundwater inflow has occurred in <br />the caved zone created by longwall mining indicating that there is little to no <br />groundwater in the materials overlying the mined B Seam coal. <br />2. Fractured Zone - A zone of fracturing and local sepazation along rock bedding planes and <br />joints occurs above the zone of caving and is termed the "Fractured Zone." Here, lateral and <br />vertical constraints within the adjacent overburden strata and the caved rocks below <br />minimize further displacement or rotation of the fractured rock. As such, displacement and <br />severity of fracturing tends to decrease upwazd as lateral and vertical confining stresses <br />increase. As a transitional zone, groundwater within permeable units closer to the caved <br />zone will tend to be more affected (lost to the mine workings) than those at greater distances <br />above the caved zone. In many cases, induced groundwater drainage (particulazly in the <br />upper part of the fractured zone, in the shale sequences between sandstone layers) will cease <br />as the water-bearing zone is restored following bed recompression and closure in response to <br />overburden load and subsidence completion. Evidence of restored water levels has been <br />reported in some wells in the West Elk Mine area after completion of F Seam retreat mining <br />and subsidence. <br />3. Continuous Deformation Zone -The continuous deformation zone is located between the <br />fractured zone and the surface. In this zone the strata deform without causing any major <br />continuous fracturing through the thickness of the strata, as is the case in the fracture zone. <br />Thus, the strata behave essentially as a continuous medium causing little, if any, disruption of <br />groundwater movement. Surface or tension cracking may disrupt water-bearing formations <br />within this zone, potentially causing downward migration of groundwater between permeable <br />units. <br />4. Near-Surface Zone (or Zone of Surface Cracking) -The "near-surface zone" typically <br />consists of weathered bedrock, colluvium, and soil ranging in depth from a few feet to a few <br />tens of feet, which may deform differently than the underlying bedrock, especially on steep <br />slopes. Within the neaz surface zone, movement can best be described as "elasto-plastic" in <br />nature. The neaz-surface strata aze typically draped over the underlying strata, and they <br />follow these strata downwazd in broad "S-shaped" curves. As in the continuous deformation <br />zone, groundwater within the colluvium or weathered bedrock may be disrupted by surface <br />cracking and diverted to permeable units deeper in the overburden. <br />Mine Inflows <br />Historically, mine inflows have been of relatively small scale and short duration. Until the spring <br />of 1996, when more than 2,500 gpm of water entered the mine through a fault system in the <br />i eastern portion of the mine (B East Mains), there had been no reason to plan for managing lazge <br />2.05-248 Revised Jura 2005 PRIO; Rev. March 2006; Rev. May 2006 PRIG <br />