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-59- but proposes to prevent damage to significant permit area features such as the Dry Fork of Minnesota Creek, and Beaver and Minnesota Reservoirs, by utilizing a limited extraction plan beneath these critical features. This limited extraction will ensure that no adverse effects of subsidence will occur. The subsidence evaluation prepared by WECC reflects the current state-of-the-subsidence-prediction-art. It includes an analysis of pillar strength in areas proposed for protection by limited extraction withuut pillar recovery upon retreat. The originally approved WECC plan also included the installation and monitoring of the subsidence monitoring network over the first panel to be fully mined, during the third year~of the first five-year permit period. Data from this monitoring network is to be utilized to verify the design of the buffer zones proposed beneath the Dry Fork of Minnesota Creek and to predict the magnitude of subsidence and subsidence phenomena to be expected throughout the remainder of the lease property. Additional future subsidence monitoring networks shall also be proposed for the Dry Fork area to assure that subsidence impacts are prevented. As a portion of its November, 1984 permit revision application, WECC proposed a relocation of the originally required subsidence test panel and accompanying subsidence monitoring network. Reconfiguration of the underground mine plan, necessitated by an approved reorientation of the mains to avoid an area of bad coal and roof conditions, has resulted in a need to relocate the first panel to be subsided. The relocation is not significant, allowing the originally installed ground water monitoring wells to serve their original purpose, monitoring ground water response to subsidence of the test panel. However, the surface subsidence monument locations required amendment. The amended monitoring network is depicted in Figures 7, 8 and 9 of Appendix A to WECC's November, 1984 permit revision application. A row of monuments installed parallel to the axis of the test panel will be spaced on 100-foot centers. Two rows of monuments will transect the test panel and will be spaced on nominal 50-foot centers. These transverse monument rows will extend to the east of the panel centerline above the mains and tb the west for at least 750 feet to the west of the panel centerline. WECC will tie the monitoring to a network of more permanent surveying triangulation bench marks to be established beyond the area of potential subsidence influence. Resurveying of triangulation monuments will be performed annually, to allow correlation of semi-annual aerial photogrammetric surveys discussed hereafter. WECC commits to two pre-subsidence field surveys of all monitoring points and annual resurvey of triangulation monuments with Second Order Class II horizontal accuracy. WECC commits to achieving vertical error no greater than + 0.2 feet. WECC will compare these field survey results with the results of an aerial photogrammetric survey of the monument grid. In order to avoid misunderstanding, '~ , .. . ~ ..