REV07929 - Laserfiche WebLink

Home Browse Search

West Elk Mine The greater the overburden thickness, the smaller the probability that fractures from the mined area will reach the rechazge source for any given colluvial spring. Within the South of Divide permit revision area, the overburden above the E Seam is relatively thick, thus all but eliminating the probability ofmining-induced impacts on colluvial springs. Within the current pemut azea, including the Box Canyon revision area, greater minimum distances between the B Seam mining and surface flows are maintained with the exception of the Gribble Gulch azea, west of the 7NW longwall panel. In this azea, the minimum 300 feet of B Seam overburden provides little buffer between the combined caved/fractured zone height and the known springs. Detailed monitoring of this azea during mining will allow MCC to assess potential impacts to well springs in the upper fractured zone and to support or refine predicted effects. There is a higher probability that colluvial and alluvial springs will be impacted by surface cracks, although this risk is also quite small, for the many reasons that aze presented in Section 2.05.6 (3)(b)(iii & viii) Surface Water Quantity Effects, Streams. Consider the following factors: 1. It is not feasible to quantify the probability that a spring will encounter a surface crack. However, as with stream channels and stock ponds, the probability that a spring in the mining azea will encounter a crack is quite small. 2. Spring flows that enter a crack will continue to move downgradient, leading to spring relocation rather than spring loss. 3. Cracks that do occur are likely to be found in association with chain and barrier pillars. The evidence from the northwest longwall panels 1 through 8 and experience elsewhere, indicates the probability of cracking within the internal portions of the panels is much lower. This will facilitate crack monitoring and mitigation. 4. In the unlikely event that cracks do develop within the internal portions of the panels, there aze various "healing" mechanisms, which will act to fill in the crack within a few months. 5. Although surface cracks located over the pillars are less likely to "heal" themselves, they will fill in over time via "sealing" mechanisms, principally in the form of sediment inflows. 6. Most spring flows which infiltrate into surface cracks will re-emerge downgradient; consequently, the water will not be "lost" to the basin, which is important from a water rights standpoint. In short, it is very unlikely that the rechazge source for any given alluvialfcolluvial spring or spring itself will encounter a surface crack. If this does happen, however, the ameliorating factors listed above will apply. 2.05-I70 Revised June 2005 PRlO