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<br />III.A.7.k Subsidence Effects on the Powerline. A need to re-orient the mine plan impacted the <br />initially proposed non-subsidence corridor. Either considerable longwall tonnage would be eliminated <br />or the concept of anon-subsidence corridor had to be abandoned. To ensure that maximum <br />economic recovery of the coal is achieved, BME chose the latter alternative. <br />As discussed elsewhere, the waterline could be protected from subsidence either by relocating <br />underground or constructing an offset Tine to bypass any affected portion of the waterline. However, <br />relocation of the 138-Kv powerline was not economically feasible and portions of the powerline were <br />allowed to subside with mitigative measures in place. In actuality no effect of subsidence was noted <br />on the waterline during the mining of LW-1 to LW-5. <br />An analysis of subsidence effects on the 138-kV powerline indicated that some of the pole structures <br />would be affected by the subsidence. The worst possible consequences of subsidence to the power <br />line would be the interruption of power supply to the mine. The consequences of such a power failure <br />would be the same as those experienced in past power failures; the mine would be evacuated of all <br />personnel until the power supply is reestablished and all safety procedures determine that the mine is <br />safe to reenter. <br />There are a total of 28 structures within the permit boundary on the 138-kV powerline. Of this total, 11 <br />• structures are in positions where they could have been affected by subsidence. The structures are <br />bolted wooden two-pole structures with connecting crossbraces. BME owns the structures and lines <br />and is the only customer served by the powerline. <br />On the north-south leg of the powerline, two structures and possibly a third were expected to be <br />affected by longwall subsidence. One structure overlies room-and-pillar area 2 (RP-2). Two structures <br />are within the outline of longwall panels 1 and 2 (LW-1 and LW-2) and initial tilting toward the <br />southwest was expected as the subsidence wave passed them. As subsidence is completed they <br />were expected to return to a vertical or near vertical orientation. The third structure was on the edge of <br />the subsidence. The three structures over the longwall panels, as discussed above, were to be <br />affected in 1987, 1988 and 1989. No tilting of the structures due to longwall mining was observed <br />during active subsidence. <br />• i6narerrrr K~r~~w t~~~v~;~~ m' <br />