The Laramie Energy Technology Center is conducting field tests of in situ coal gasification, oil shale retorting, and recovery of bitumen from tar sands. In situ processes involve several potential hydrologic impacts; the complex series of underground chemical reactions will affect ground water quality, and heat from the reaction zone and fracturing necessary to improve reaction conditions will alter existing aquifer characteristics and ground water flow patterns. Disposal and handling of solid and liquid wastes generated by the processes may also involve significant hydrologic impacts.