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Jim Herron -2- September 20, 1983 <br /> (3) The current subsidence monitoring scheme will not allow determination <br /> of an angle of draw sufficient to discern between the operator's projected <br /> 150 from vertical and the imposed 20.50 angle of draw. Closer spacing of <br /> subsidence monuments would be required in order to accomplish the necessary <br /> discrimination. <br /> The operator' s proposed monitoring plan amendment requests "that only those <br /> points in close proximity to areas from which coal is being extracted be <br /> monitored at the frequency now specified in the approved plan (see map), and <br /> that those remote stations outside the area of mining influence (computed with <br /> a draw angle of 350) be surveyed only in the last year of the permitted <br /> five-year plan." The amended subsidence monitoring net map IV-F-2 indicates <br /> cessation of monitoring of monuments MC-1 and MC-5 through MC-9. Monuments <br /> MC-5 and MC-6 have demonstrated subsidence movement in both 1982 and 1983 <br /> observations years. In order to determine whether additional subsidence <br /> adjustments occur, and at what relative rates, these two monuments should be <br /> monitored until cessation of movement has been demonstrated. Monitoring of <br /> monuments MC-1 and MC-7 through MC-9 can be ceased until the final year of the <br /> permit term. <br /> The subsidence report prepared by Mine Subsidence Engineering Company observes <br /> that control point TP-5, used to survey monuments MC-1, MC-2 and MC-3, has <br /> subsided. The operator must reestablish control appropriate to continue <br /> monitoring of those three monuments, in order to allow completion of next <br /> season's monitoring. <br /> The operator proposes the installation of six additional monuments, MC-10 <br /> through MC-15, indicated on the amended subsidence monitoring net map IV-F-2 <br /> in green, not red as indicated in the letter requesting amendment. These <br /> subsidence monitoring points should be installed and surveyed for control as <br /> soon as possible this fall. These monuments shall be installed as depicted <br /> and described in "Characterization of Subsidence Over Multiple Lift Longwall <br /> Panels" by Collin Stewart of Mine Subsidence Engineering Company. <br /> It is imperative that the proposed subsidence monument installation and <br /> reestablishment of survey control be accomplished as soon as possible. It is <br /> unfortunate that the operator did not submit a more appropriately timed <br /> request for amendment. The submission, dated September 12 and received by the <br /> Division September 14, 1983, allows little time to accomplish the required <br /> tasks. The operator is reminded that compliance with the approved subsidence <br /> monitoring plan remains the responsibility of the operator. Failure to <br /> complete the proposed subsidence monument installation and survey control <br /> reestablishment this fall may result in loss of valuable subsidence data, <br /> which might be extremely important in resolving future permitting-related <br /> subsidence questions. <br /> /mt <br /> cc: Brian Munson <br /> Doc. No. 5669 <br />