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sandstone beds are generally discontinuous and widely spaced. Locally, however, the massive sandstone units display <br />numerous, closely spaced joints. The orientation of jointing appears to be near vertical. In summary, the overburden <br />geology in the planned longwall mining area is similar to that which occurs throughout the EC Mine complex. <br />Local Mining Experience <br />Local mining experience concerning subsidence occurrence can be divided into two (2) categories: 1) subsidence <br />resulting from mining in the EC Mine complex prior to EC's acquisition of the property (prior subsidence) and 2) <br />subsidence resulting from EC's operation (monitored subsidence). <br />Prior Subsidence. Trough -type subsidence has occurred where full -extraction room -and -pillar mining has been <br />conducted in the Wise Hill No. 4 Mine. In these areas, no surface subsidence features or damages can be identified <br />even though the full -extraction was relatively near the surface. Similar subsidence has been experienced over the full - <br />extraction areas of the No. 5 Mine, although some superficial effects, consisting of cracking are evidenced. <br />Although minor dewatering of the sandstone aquifers may have resulted from previous subsidence occurrences, no <br />noticeable or significant effects have been experienced. In addition, no material damage has resulted from previous <br />subsidence occurrences. Hydrologic monitoring Well 259 (as shown on the Subsidence Monitoring Map (Map 31)) <br />continues to flow from approximately 85 feet deep, which indicates that the caving experience in the Wise Hill No. 4 <br />Mine has not had a significant effect upon the overlying aquifer. <br />Monitored Subsidence. EC has and continues to conduct detailed subsidence monitoring throughout the EC Mine <br />complex. Monitoring of mining -induced subsidence has been conducted in areas of: <br />• Full -extraction room -and -pillar mining (F -seam workings), <br />• Longwall mining under non subsided ground (F -seam workings, and <br />• Longwall mining underground subsided by previous mining in the E -Seam workings. <br />The results of these subsidence monitoring programs (refer to Map 31) have been provided to the State in semiannual <br />and annual subsidence monitoring reports. The results are summarized briefly in this section. <br />Subsidence monitoring above full -extraction room -and -pillar mining in the F -seam workings was conducted in the <br />third East area. The results of this monitoring indicated that for an extraction height of from eight to ten feet and an <br />approximate extraction ration of 80 percent, the magnitude of maximum subsidence was 4.8 feet. The only visually <br />observable surface effects were some surface cracks associated with this subsidence. This surface cracking generally <br />occurred above the barrier pillar ribsides. The maximum width of the cracks was one foot. The vertical offset across <br />the cracks was less than one foot. The cracks tended to close up after about 24 months. <br />Subsidence monitoring of longwall mining in the F -seam workings was conducted above longwall panels 12 East, 13 <br />East, and 14 East. This monitoring represents mining of longwall panels under previously non subsided ground. The <br />monitoring indicated that for an extraction height of approximately 10 feet, the magnitude o maximum subsidence was <br />from 6.5 to 7.5 feet. Surface cracking has been associated with this subsidence. In general, the cracks tended to <br />parallel the surface topography. Surface cracking was best developed where sandstone beds lie at or near the ground <br />surface. <br />Subsidence monitoring of longwall mining in the E -seam workings continues at this time. It was conducted above <br />longwall panels I East and 2 East. This monitoring represents mining of longwall panels under two overburden <br />conditions: (1) ground subsided previously by F -seam longwall mining, and (2) ground with partial extraction room - <br />and -pillar mining in the F -seam. <br />The monitoring indicated that for an extraction height of approximately 10 to 10.5 feet, the magnitude of maximum <br />subsidence was from 9 to 9.5 feet under previously longwall mined overburden. <br />Permit Revision 04-34 2.05-57 Revised 7/2/04 <br />