Laserfiche WebLink
West Elk Mine <br />• Within the South of Divide pemut azea, the height of the caved zone above E Seam mining is <br />conservatively estimated at 3t or 42 feet. The height of the fractured zone above the longwall <br />panels is conservatively estimated at 20t or 280 feet when t =14 feet. <br />This can be compazed with the minimum overburden thicknesses in the mine plan azea. <br />Minimum overburden thickness above the E Seam in the South of Divide permit area is 375 feet. <br />This comparison demonstrates that fractures extending upward from the mined area would not <br />impact streamflows. <br />Analysis of Impacts to Streams <br />Subsidence in the South of Divide permit revision area has the potential to affect streams in <br />two ways. Fractures, which extend upward from the mined seam may intersect the stream or, <br />more likely, surface cracks may develop which intersect the stream. The principal problem that <br />longwall-induced subsidence creates with respect to streamflows is surface cracks that may cause <br />the loss (normally on a temporary basis) of surface flows. WWE, working closely with Messrs. <br />Rold and Dunrud, has evaluated the phenomenon of surface cracking in association with longwall <br />mining at West Elk Mine and has referred to comparable experience in the North Fork Valley and in <br />the relevant literature. It is WWE's general conclusion that, in the permit azea, there will be very <br />little modification of the existing surface water flow regime as a consequence of surface cracks <br />caused by mining. <br />• As discussed in Section 2.05.6 (6)(b)(i), Description of Possible Subsidence Consequences, surface <br />cracks resulting from longwall mining subsidence aze infrequent at the mine. In fact, where <br />cracks have formed above longwall panels, additional factors have usually played a role. <br />• The crack above the east side of 1NW longwall panel was influenced byroom-and-pillar mining <br />in the F Seam. <br />• The cracks along the southern edge of Section 17 had influence from both MCC's F Seam <br />mining and Beaz's B and C Seam mining and the barrier pillars between them. <br />• The cracks located between SNW and 6NW longwall panels were most likely caused by the <br />reinitiation of an old landslide. <br />• The cracks above 8NW longwall panel that CDMG had eazlier attributed to subsidence were in <br />areas of low overburden and within a lazge old landslide mass. Other cracks have been <br />observed within the old landslide mass that is completely outside the mining azea of influence. <br />Therefore, when assessing the potential for surface cracks due to longwall mining subsidence, the <br />presence of mitigating factors must be considered, such as existing landslide activity, adjacent to or <br />overlying mine workings, and very low overburden. <br />An additional factor in predicting the probability of surface cracking is the location with respect to <br />the longwall panel layout. With the exception of two of the 8NW longwall panel cracks, all of the <br />cracks were located above chain or barrier pillars, where stresses are maximised. The only cracks to <br />2.05-I59 Revised Jwe 2005 PRIO <br />