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/wnc 1991 Cj~pnv 7'~CC •Anolysir o/'Sw6srdrnce E/fav on HJdrology • 4 <br />According to Singh (1986), the ara of disturbance above a longwall panel is generally divided <br />into the following five zones, based on the eaten[ of fracturing: <br />ZONE 1 -Zone of primary raving where the pved rock is completely disintegrated; <br />ZONE 2 -Zone of bed separation where sepazation occurs primarily along pre-atisting <br />bedding planes; <br />ZONE 3 -Zone of vertical relaxation where a slight increase of permeability is <br />experienced; <br />ZONE 4 -Zone of horizontal extension where shallow fractures may develop at the <br />surface; <br />ZONE 5 -Zone of horizontal compression where shallow fractures may develop ac the <br />surface. <br />For the Foidel Creek Mine, these zones are illustrated by Figure 3, Cross-Section B-B'. <br />Based on international experience, the total thickness of the first and second zones, where <br />significant changes in permeability typically occur ranges from 3 [0 3.5 limes (Ropski and Lama, <br />1973), to a maximum of 10 times the height of the eatracted seam (Wardell, 1976). <br />The height of the third zone, or the total height where any significant changes in permeability <br />due to subsidence can occur, is described by various authors as ranging from 30 t to 60 t, where <br />t is the fully extracted seam thickness (58 t-Gviroman, 1977, 33.7 t-Williamson, 1978, and 30 [- <br />Wardell, 1976). <br />Results of studies performed in the Appalachian bituminous coal region are consistent with <br />documented international research. A study of subsidence in the Dunkazd Basin (Owili-Eger, <br />1982) concluded that water levels in aquifers located within 330 feet above the mined coal <br />recovered after mining, and that there was no lasting deterioration of ground water quality. <br />Another study of subsidence in Western Pennrylvania (Hill and Price, 1983) concluded that, <br />with an average thickness of the overburden of 550 feet, the shallow aquifer rystem was isolated <br />from any significant mining related impacts. These authors also observed that for wells which <br />are undermined by longwall operations, once mos[ of the subsidence occurs the affected strata <br />settle and ground water levels rebound as reconsolidationcorastricts and eliminates flow paths. <br />Stoner (1983) performed a study of subsidence due to mining in the Pittsburgh Seam in Greene <br />County, southwestern Pennsylvania. During [he study he monitored a well located above a <br />longwall panel. The water level in the monitored well declined during undermining but <br />returned to within 3 feet of the pre-mining level when mining advanced beyond the well. <br />The U.S. Bureau of Mines (Walker, 1988) monitored surface svbsidena and water level <br />fluctuations in 10 shallow observation wells above a series of four adjacent longwall panels in <br />southern Pennsylvania, for about 4 years. Results of this study indiate that wells are generally <br />unaffected by mining of a preceding panel. The most important conclusion of the study was <br />• that nine out of the ten wells investigated recovered to pre-mining water levels after mining was <br />completed. <br />ACZ Inc. • P.O. Bos 77!018 • Stvmbaot Springx Colorado 80477 • (303J879-6260 <br />