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• The Staley Gordon Mine, abandoned in 1970, was mined using the room and pillar method. There is no detected subsidence above the abandoned mine although the overburden thickness is less than 200 feet and there are large caved areas in the abandoned mine. This indicates that the subsidence caused by small room and pillar sections will have minimal visual impact on the surface. However, the subsidence caused by the abandoned Staley Gordon Mine cannot be compared to the expected subsidence of the Deserado Mine because of its much larger scale of coal extraction. The highest recovery in caved pillar robbing areas of the Staley Gordon Mine was determined from the mine map to be approximately 68%. To calculate the maximum predicted surface subsidence and strain, a more conservative recovery of 75% was used. Using the actual depth of 300 feet at this location and a mining height of 6 feet, a maximum tensile strain of approximately 1700 micro-strains should be produced. This amount of tensile strain probably caused some surface cracks to open up. Since the mining and subsequent subsidence occurred more than ten years ago, normal weathering of the surface would have erased any surface cracking or other visible evidence of subsidence. This has in fact been found to be true; a visual inspection of the surtace over the caved areas showed no surtace cracks, tilted trees or other indications that subsidence had even occurred. III.A.7.c Subsidence Prediction. Predictions of the maximum surface subsidence and horizontal tensile strain for the Deserado Mine D Seam and B Seam longwall panels are presented in Table III-1. Map No. 119 and 120 show the locations of these panels within the mine. These predictions are based on results of subsidence studies made by the U.S. Bureau of Mines and on the model produced by the British National Coal Board. The USBM studies were conducted in underground coal mines having similar geologic conditions as that found in the Deserado Mine. The NCB model is based on 187 subsidence profiles measured across 165 longwall panels. The Deserado Mine subsidence predictions were derived primarily from the British National Coal Board model with input from a model developed by the U.S. Bureau of Mines at the York Canyon Mine. The predictions rely more heavily on the NCB model which is based on 187 subsidence profiles measured across 165 longwall panels. The York Canyon model is based on information collected from only 11 profiles. It is recognized that the British model is for their Carboniferous strata, whereas the Deserado Mine strata is late Cretaceous and Tertiary. The Cretaceous formations found in the U.S. are generally stronger than the British Argillaceous strata. (The Deserado Mine Mesa Verde formation above the coal seam is discussed in the geology section of this application.) • Permit Renewal #3 (Rev, 8/99) III-11