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Subsidence and Geologic Field Observations <br />Apache Rocks and Box Canyon Mining Areas <br />July 12-15, 2004 <br />upper reaches of Sylvester Gulch above mined longwall panels 15 and 16 (overburden depth to <br />the BSeam-about 900 to 2,000 feet). Also, the two stock watering ponds located above the <br />headgate entries of mined longwall panel 15 (Twin Ponds) showed no noticeable water level <br />difference compared to annual observations in years prior to the mining of longwall panels 15 <br />and 16. The clays and silts, derived from the Wasatch Formation, provide a good yieldable seal <br />for the ponds when [he underlying longwall panels are mined. <br />No landslides in the Apache Rocks mining area were noticeably affected by longwall mining. <br />No recent cracking or bulging was observed as of July 15, 2004. The cracks, bulges, and steps <br />observed on the landslide terrain on the north side of Minnesota Reservoir and the landslides <br />north of un-mined longwall mining panels 18A, 18, and 19~utside any mining influence- <br />have caused a much greater impact on the surface than any of the subsidence features observed <br />during the subsidence field studies of the last nine years (1996 through 2004). <br />Based on this historic information, in regard to mining effects on landslides, no effects on the <br />landslides located south of the North Fork of the Gunnison River (the Highway 133 landslides), <br />are expected if longwall mining panels 18, 18A, and 19 are mined in periods of normal <br />precipitation. Should these longwall panels be mined during a very wet period, renewed <br />landslide activity could occur. However, based on the conclusion that very little, if any, effects <br />were observed on landslides on Jumbo Mountain during the mining of longwall panels 8 and 9, <br />any renewed landslide activity would be primarily due to natural causes. <br />Recent activity in the rockfall and landslide area on the headwall azea of the first east side canyon <br />of Sylvester Gulch was likely caused, at least to some degree, by mining in longwall panel 22. <br />' Comparison of photos taken in July 2003 (prior to mining) and July 2004 (after mining was <br />completed beneath the rockfall/landslide area) show rockfall and some slide activity, which <br />indicates an acceleration of natural rockfall activity. The natural rockfall process in this area <br />(with an already very high natural rockfall potential~an area with the highest cliffs and steepest <br />' slopes in the Apache Rocks and Box Canyon mining areas- may be further accelerated when <br />831-032.640 Wright Water Engineers, Inc. Page 47 <br />^ September 2004 <br />