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~.. <br />Subsidence ~lonitorin <br />While ARCO plans to prevent any subsidence effects under the Dry Fork, <br />Norse Creek and South Prong stream channels, detailed subsidence <br />information will be gathered over the life of the mine. This will <br />allow the mine plan and design to be adjusted as new information on <br />subsidence effects is obtained. The mine plan calls for mining to _ <br />proceed throughout the lease block in a counter-clockwise manner. <br />Approximately ten years will elapse before the mains, "limited <br />mining", extend beneath the Dry Fork and approximately 11 years before <br />active mining takes place around the western course of Dry Fork. It <br />will be another 29 plus years before mining is projected to occur <br />under the eastern half of Dry Fork. Therefore, ample time will be <br />available to gather subsidence data prior to mining in the vicinity of <br />Dry fork. <br />The subsidence program will consist of establishing a neiwork of sur- <br />vey monuments to monitor any vertical and horizontal displacements. <br />The first net:vork will be installed over the first panel to be fully <br />mined, with other net:orks established at appropriate locations as <br />mining progresses. Data from these networks will be used to verify <br />the design of the buffer zone under the Dry fork and predict the <br />magnitude of subsidence effects expected over the rest of the pro- <br />perty. <br />As an additional precaution, a subsidence monitoring network is <br />planned for the Dry fork area to assure that no adverse impacts affect <br />the stream channel as mining approaches the area. <br /> <br />(13) <br />