PERMFILE42013 - Laserfiche WebLink

Home Browse Search

Subsidence Evaluation For Exhibit 608 South of Divide Mining Area Page 22 through ES (located in parts of Sections 3, 4, 9, and 10, Township 14 South, Range 90 West). 7. This azea contains 3 rockfall azeas that have an estimated Iow to [ugh rockfall potential. It is located in the Lick Creek azea south of any cun•ently planned mining (located in parts of Sections 8, 9, and 16, Township 14 South, Range 90 West). Of the seven azeas listed above, six occur near local drill roads or agricultural access roads, which have only local, limited traffic on them. Any rocks that may fall in these azeas could be readily removed before local traffic is impacted, should rockfalls occur on these remote roads. Evidence of naturally occurring rockfalls, such as remnant boulders located at the base of steep slopes, or in the run-out zones of these azeas, should be documented prior to mining. Based on annual observations in the Apache Rocks and Box Canyon mining azeas during the last six yeazs (1999-2004 inclusive), subsidence and any seismic activity caused by longwall mining is not expected to significantly affect rockfall azeas with an estimated high to low rockfall potential. Only rockfall azeas with an estimated very high rockfall potential were noticeably affected. However, because there are no rockfall azeas in the South of Divide mining azea with an estimated very high rockfall potential, the planned longwall panels in this mining area will most likely not be affected. It is suggested that signs stating, "Watch for Falling Rock," be posted in strategic places along the more well traveled roads, such as the roads along the main fork of Minnesota Creek, Dry Fork and Lick Creek, before mining begins. This procedure would be similaz to signs posted along such major interstate highways as I-70 in the Glenwood Canyon area, where the rockfall potential and risk to travelers is high to very high (compared to low to very low risk to travelers in the South of Divide mining azea). 10.3 Importance of Baseline Landslide and Rockfall Data The most significant landslide in the South of Divide area, in terms of proximity to man-made structures, is located above the northern pazt of longwall panel E9 (Map 1). Although there is a lazge landslide within the azea of mining influence of the southeast comer of un-mined longwall panel E8 (mostly in the NEYa of Section 8), the landslides located north and south of Minnesota Reservoir aze the most important in the mining azea. It is important to monitor the existing, natural (baseline) conditions before mining begins in order to document their natural state. The cracks, bulges, and depressions observed in the landslide azeas north and south of Minnesota Reservoir aze much more extensive and dramatic than those caused by subsidence. The vertical aerial photographs obtained by the West Elk Mine {dated July 2, 2004) will provide good baseline images of all the natural, pre-mine features in the South of Divide mining azea. Observations made by the author in the West Etk mining area indicate that mining may accelerate the natural landslide process, where there are landslides that have already become unstable. However, annual observations of the surface cracks and depressions in the landslide azea on 831-032.620 Wright Water Engineers, Inc.