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4.0 SUBSIDENCE MONITORING PROGRAM (RULE 2.05.6(6)(c)) <br />• The purpose of the subsidence monitoring program is measure <br />surface subsidence effects and to verify the accuracy of initial <br />predictions under actual ground conditions. The program is <br />designed to yield subsidence data that can be used to predict <br />effects of both development and retreat extraction methods. <br />Two lines of surface monuments are planned for each of two <br />areas, one line along the center line of a long axis of the <br />panels, and one cross line over the panels. All lines of <br />monuments will extend 0.7 times the depth beyond the panel rib <br />sides and the end lines. Extension of the monuments to 350 <br />beyond the rib sides and end lines will ensure that the limit of <br />subsidence will be determined. Thirty five degrees is the <br />maximum angle of draw predicted by the NCB. <br />• The sites selected for monument installation are <br />representative of the mining conditions (i.e., width to depth <br />ratio and mining thicknesses) present as a result of mining the <br />Red Arrow coal seam and the Dirty Jack coal seam. One monument <br />grid was located outside the limits of the old mine workings to <br />determine the effects under known control conditions. The second <br />was located over old mining and in an area with low overburden <br />depths. This area is representative of conditions under the <br />refuse pile area. The two locations were also selected because <br />development and production mining will occur in those areas <br />within the near future. Single monuments are also proposed at <br />locations of existing key structures to record magnitudes of <br />• subsidence as a result of the effects of proposed mining. All <br />mining locations are shown on the mine plan and topographic map <br />30 <br />