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.• <br />Carol Russell -2- March 2, 1981 <br />If WSC intends to rely upon roof bolting to maintain roof control and prevent <br />subsidence in these additional entries, the survey monuments pictured in <br />Figure 4.20.1-A will have to be installed prior to excavation of those entries. <br />If any subsidence were detected in subsequent monitoring of the survey <br />monuments installed along that highway WSC will be required to install appropriate <br />steel arch support and to repair damage to the highway initiated by subsidence <br />events. If the monuments depicted in Figure 4.20.1-A have been installed, the <br />application should include monitoring results listing a location and any affects <br />to date. <br />~(5) Western Slope Carbon's permanent permit application states that in several <br />places that subsidence monitoring need only be continued for twelve months <br />following the cessation of mining beneath any monument. No rock mechanics data <br />is provided to justify such a statement. '.The monitoring suggested does not <br />satisfy the requirements of Pule 2.05.6(6)(c)(i)(F). The results of the subsidence <br />monitoring program will determine when cessation of observations at any <br />monument becomes appropriate. <br />mab <br />cc: Ed Bischoff <br />