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<br />-54- <br />As a portion of its November, 1984 permit revision application, <br />WECC proposed a relocation of the originally required subsidence <br />test panel and accompanying subsidence monitoring network. <br />Reconfiguration of the underground mine plan, necessitated by an <br />approved reorientation of the mains to avoid an area of bad coal <br />and roof conditions, has resulted in a need to relocate the first <br />panel to be subsided. The relocation is not significant, allowing <br />the originally installed ground water monitoring wells to serve <br />their original purpose, monitoring ground water response to <br />subsidence of the test panel. However, the surface subsidence <br />monument locations require amendment. The amended monitoring <br />network is depicted in Figures 7, 8 and 9 of Appendix A to WECC's <br />November, 1984 permit revision application. A row of monuments <br />installed parallel to the axis of the test panel will be spaced on <br />100-foot centers. Two rows of monuments will transect the test <br />panel and will be spaced on nominal 50-foot centers. These <br />transverse monument rows will extend to the east of the panel <br />centerline above the mains and to the west for at least 750 feet to <br />the west of the panel centerline. WECC will tie the monitoring to <br />a network of more permanent surveying triangulation bench marks to <br />be established beyond the area of potential subsidence influence. <br />Resurveying of triangulation monuments will be performed annually, <br />to all crrelation of semi-annual aerial photogrammetric surveys <br />discussed heraafter. <br />WECC commits to two pre-subsidence field surveys of all monitoring <br />points and annual resurvey of triangulation monuments with Second <br />Order Class II horizontal accuracy. WECC commits to achieving <br />vertical error no greater than + 0.2 feet. WECC will compare these <br />field survey results with the results of a aerial photogrammetric <br />survey of the monument grid. In order to avoid misunderstanding <br />the Division has imposed a stipulation defining the accuracy <br />standards to be achieved in completing both the field and aerial <br />photogrammetric pre-subsidence surveys. <br />Further, the Division believes the photogrammetric subsidence <br />monitoring technique to represent an interesting potential <br />technical innovation. However, the technique is unproven for the <br />completion of subsidence monitoring surveys. Therefore, the <br />Division believes it prudent to require the applicant to correlate <br />its aerial photogrammetric monument surveys to traditional ground <br />survey monitoring of selected triangulation monuments. In order to <br />avoid misunderstanding, the Division has imposed a stipulation <br />defining the accuracy standards to be achieved in completing <br />post-subsidence aerial photogrammetric surveys of the subsidence <br />monumentation grid. <br />Subsequent to the original submission of exhibit 3.4.8.A, the <br />Division addressed additional concerns to WECC regarding the <br />possible effects of subsidence upon landslide deposits neighboring <br />Beaver and Minnesota Reservoirs. WECC responded in letter form <br />indicating that it desires that the final designation of possible <br />