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Subsidence_Report___Longwall_Area Longwell subsidence and slope monitoring points were installed and surveyed in the fourth quarter of 1984. The location of these points and the advancement of the first longwall panel ere shown on the enclosed map titled "Longwell Subsidence Topo Map", drawing number 8519-LS. The monuments have been surveyed on a quarterly basis since the longwall began production in May, 1985. The results of the data obtained from these three surveys is included in this report. I Results of the June survey indicate that no detectable subsidence took place during the second quarter of 1985. This is attributable to the fact that the longwall had only advanced 580 feet by the end of June. By the end of September, the longwall had advanced a total of 1,530 feet since production began. The September survey results clearly show that subsidence had occurred as evidenced by the change in elevations of monuments R-2 through R-14. The maximum subsidence detected was 4.4 feet. Visual observations during the September survey revealed that I subsidence cracks had developed on the surface above the longwall area. These cracks have been surveyed and their locations are shown on the Longwell Subsidence Topo Map. By the end of 1985, the longwall had advanced a total of 2,750 feet. The December results show that subsidence continued as the longwall advanced. The enclosed drawing, "Subsidence Monitoring Profiles", number 8518-5MP, depict the measured vertical changes of each of the monitoring rows. The cross-sections are based on the December, 1985, survey results. The maximum subsidence for the affected rows are as follows: ' Maximum Row Subsidence Comment --- ---------- ------- R 6.08 ft. Pt. located downdip of panel centerline NPR 5.13 ft. Centerline of panel R 6.11 Pt. located downdip of panel centerline The cross-sections show that the original ground. has dropped ' as much as one foot in elevation in areas that should show no subsidence. It is apparent that these changes in elevation are due mainly to suface settlement. This is to be expected since many of the monuments are located on reclaimed spoil from strip mining.