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Coal Board (NCB) and U.S. Bureau of Mines modeling. The operator has predicted up to <br />7.7 feet of surface subsidence for longwall mining azeas and up to 0.5 feet of subsidence <br />for room and pillaz mining azea. Based on predicted horizontal tensile strains, surface <br />cracks up to several inches wide aze anticipated within zones of maximal subsidence, with <br />the extent of cracking dependent on the nature of neaz surface geologic strata and surface <br />soil cover. <br />Measures employed to prevent subsidence material damage are addressed in Section <br />III.A.7.g, of the application, and include a network of permanently supported mains and <br />submains, barrier pillazs, chain pillars, and unmined coal blocks in specific azeas. The <br />operator has committed to a program of visual monitoring to identify subsidence caused <br />damage to surface structures, stock ponds, and major drainages, and has committed to <br />repair hazardous tension cracks, subsidence features interrupting flow in Red Wash or <br />Scullion Gulch, or damage to surface structures. <br />The Probable Hydrologic Consequences section of this Findings Document addresses <br />monitoring results of subsidence in Red Wash. In summary, clay and silt quickly filled in <br />depressions and cracks that appeared in Red Wash as a result of subsidence, and the <br />channel has not been significantly altered. Similaz subsidence effects aze expected for <br />Scullion Gulch. The operator has committed to conduct visual monitoring at least twice <br />per week upon commencement of longwall retreat mining on Panel LW-IB beneath <br />Scullion Gulch, with repairs to be implemented as necessary following consultation with <br />BLM and Army Corps of Engineers. Refer to permit section IILA.7.j, for further detail. <br />The operator designed a program to yield subsidence data that would be used to verify the <br />accuracy of initial predictions under actual ground conditions, and which could be used to <br />predict future effects after monitoring the first longwall and the first room and pillaz panel. <br />The operator monitored subsidence over the first longwall panel (LW 1) using state-of-the- <br />art analytical photogrammetry. Twice per yeaz visual monitoring was employed over the <br />first room and pillaz azea (RP-1), which was mined in 1995 and 1996, and this visual <br />monitoring along with annual reporting remains in effect. LW 1 was mined in calendaz <br />yeaz 1987 and the first two months in 1988, and the monitoring conducted is described <br />below. The photograznmetric survey for L W 1 has been terminated, based on <br />documentation provided. Photogrammetric survey of RP-1 is not required, unless <br />significant unanticipated ground movement is detected. <br />Four flights were flown to record and monitor the surface over LW 1. The first flight was <br />flown during August 1986 to establish baseline conditions and base drawings for both <br />LW 1 and RPS for comparison with the future flights. The second and third flights <br />occurred in May 1987 and September 1987. Data and drawings from these flights were <br />presented to the Division in a report in December 1987 for review. The fourth flight <br />occurred in June 1988. The fourth flight information and drawings were assembled into a <br />final report and presented to the Division in October 1988. <br />Conventional semi-annual survey monitoring of five control points located within the zone <br />41 <br />