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Jwnr 1991 Cyprxr TCC • Analytic of Subsidence F~foru on Hldmfogy • 9 • It should be noted that coal is mined bcneath significant bodies of surface water, including major rivers and oceans, in many nations (Great Britain, Canada, Australia, Japan, Chile, and Turkey). The minimum cover to seabed for total extraction (longwall mining) ranges in various nations from 60 meters (197 feet) in Japan to 213.4 meters (700 feet) in Nova Scotia. Guidelines developed by [he U.S. Bureau of Mines (Wardell, 1976) state that "any single seam of coal beneath or in the vicinity of any body of rurfaoe water may be totally extracted, whether by longwall mining or by pillar drawing, provided that for each 1 foot thickness of coal seam extracted a thickness of 60 feet of solid strata cover exists between the proposed workings and the bed of the body of rurfaa water'. This means that for the Foidel Creek Mine, the proposed longwall operations would be safe under a signifiant water body given a minimum overburden thickness of 570 feet. Potential impacts of rubsidence due to longwall mining in Panels 5 and 6 on surface and ground water hydrology in the Fish Creek AVF may be summarized as follows: • Changes in Fish Creek gradient due to subsidence would have a minor impact on flow characteristic • Impacts on rurface water quality could occur only as limited increase of sediment for a shoe period of time • No impacts on bedrock aquifers underlying Fish Creek are anticipated • • Potential for impacts on the alluvial aquifer due to rurface tensile fracturing is not significant The conclusion of this study of subsidence and potential related impacts on the Fish Creek Alluvial Valley Floor is that mining in Panels 5 and 6 will not have any significant detrimental impacts on the essen[ial hydrologic functions or water availability of the AVF. 5.0 LIST OF REFERENCES Abel, J.F. Jr., and F.T. Lee, 1980. Lithologic Controls on Subsidence. SME-AIME Fall Meeting and Exhibit, Minneapolis, MN, October 22-24. Adamek, V., P.W. Jeran, and M. Trcvits, 1987. Prediction of Surface Deformations Over Longwall Panels in the Northern Appalachian Coalfield. U.S. Bureau of Mines Report of Investigations, RI 9142. Aston, T.R.C. and R.N. Singh, 1983. A Reappraisal of Investigations into Strata Permeability Changes Associated with Longwall Mining, International Journal of Mine Water, Granada, Spain, Vol. 2, No. 1. Aston, T.RC., RN. Singh, and B.N. Whittaker, 1983. The Effects of Test Cavity Geology on the In Situ Permeability of Coal Measures Strata Assodated with Longwall Mining. International Journal of Mine Water, Granada, Spain, Vol. 2, No. 4, pp. 1-18. Boettcher, A.J., 1972. Ground-Water Occurrence in Northern and Central Parts of Wes[ern Colorado. Colorado Water Conservation Board, Water Resources Circular No. 15. ACZ Inc. • P.O. Boz 77/018 • Steamboat Spring; Colorado 80177 •(303)8796160