Studies of the environmental impact of underground coal gasification (UCG), conducted at the four UCG test sites at Hanna, Wyo., by the Department of Energy, Laramie Energy Technology Center, included the effects of the process gas cleanup system, the effects of migrating water on the process and the surrounding ground water, and the effects of subsidence. In phase 2 of Hanna II experiments (Dec. 1975-May 1976), particulate matter and 14 trace elements were monitored during seven periods in order to obtain data for the necessary gas scrubbing and cleaning facilities. In the Hanna III experiments (June-July 1977) base-line aquifer and ground-water characteristics were monitored and changes in water quality and hydrologic conditions during and after gasification were determined by means of temperature, hydrostatic pressure, and conductivity tests at 12 monitoring wells. For the modified Hanna IV experiments (to be started in Aug. 1978), studies will include analyses of particulates and trace components in the product stream and of by-product hydrocarbons, subsidence monitoring, analyses of water condensed from the gas stream, and polynuclear aromatics concentrations before and after flaring.