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_ <~ <br />~~~.~,~ <br />' <br />-50- ' Vi ~ v(J~~~~ <br />Empire Energy Corporation has submitted five subsidence monitoring reports for <br />the mined areas, in compliance with the existing permit for the Eagle No. 5 <br />and No. 9 Mines. Analysis of these survey subsidence monitoring results by <br />the Division allows several observations to be made; <br />(1j Subsidence monuments installed above areas of development and retreat <br />extraction in the 3rd-East area of the Eagle No. 5 Mine, ad~oining~the <br />oil pipeline, and above the No. 9 north main, in the vicinity of State <br />Highway 13, discerned a similar subsidence response. Areas of room and <br />pillar limited development extraction demonstrated initiai vertical <br />subsidence commonly exceeding a magnitude of 0.25 feet. This initial <br />subsidence appears to manifest itself within a few months following <br />initial developmental extraction. <br />(2) Areas of limited development extraction appear to remain stable <br />following manifestation of the limited initial surface subsidence. <br />(3) Following retreat pillaring of developed areas, additional ground <br />surface subsidence was observed. Within the 3rd-East area of the Eagle <br />No. 5 Mine, retreat extraction has resulted in maximum observed vertical <br />subsidence between 2.0 and approximately 4.7'. The maximum observed <br />subsidence averaged 41 percent of the extracted seam height. <br />(4) The predictive equation developed by Abel and lee (Figure IV-12) for use <br />in predicting subsidence above room and pillar workings appears to under <br />estimate subsidence by approximately 25 percent for overburden <br />thicknesses of less than 300 feet. For overburden thicknesses in excess <br />of 400 feet, the predictive equation demonstrates accuracy within 2 <br />percent. <br />(5) The average observed angle Of draw above the 3rd East area of the No. 5 <br />Mine was approximately 200, for the three monument cross-section lines <br />monitored. <br />Empire Energy Corporation's analytical projections of subsidence within the <br />permit area present several basic conclusions: <br />(1) Initial development extraction, limited to the creation of pillar sizes <br />listed on Table IY-15, is protected to result in long term stability of <br />the underground mine workings. The applicant projects that pillars of <br />these minimum dimensions will prevent subsidence of the overlying <br />overburden, thereby preventing subsidence of the overlying ground <br />surface. <br />(2) In areas of retreat pillaring, subsidence is projected to result in the <br />maximum predicted (probable) subsidence magnitudes presented on Table <br />IV-11. <br />(3) In the event of pillar failure, which the applicant believes improbable, <br />the "worst-case predicted subsidence" magnitudes presented on Table <br />IV-11 might be realized within the permit area. <br />