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.. <br />Memo to Dan Mathews <br />Deserado Mine TR-40 <br />page 2 <br />longwall panel. Because of RP-1's thinner overburden thickness, there is a <br />somewhat higher likelihood that discrete phenomena, such as stope collapse <br />might occur. These local and discrete phenomena are easily detectible by visual <br />inspection. In my opinion, expensive repetitive aerial photogrammetric <br />monitoring is not warranted in this instance. WFU commits to continue visual <br />inspection above RP-1 and to complete any required repairs. <br />In my opinion the extensive monitoring conducted above longwall panel LW-1 <br />verified WFU's original predictive techniques and provided reliable information <br />regarding the subsidence characteristics above the Deserado mine. I recommend <br />approval of WFU's request to forego aerial photogrammetric subsidence <br />monitoring above panel RP-1 with the following conditions. The surface above <br />RP-1 shall be visually inspected twice a year. If any unanticipated deleterious <br />subsidence phenomena are detected, such as stope or chimney collapse, WFU <br />shall complete an aerial photogrammetric survey and mapping of detected <br />subsidence versus the baseline mapping, if directed by the Division. If the <br />Division requests an aerial photogrammetric subsidence survey, WFU shall <br />complete the survey and submit the map and letter report within six months. <br />Cc: Larry Routten <br />Doc: C:\WP51\COAL\WFUTR40.SU6 <br />JP/Jp <br />