The recovery of shale oil by the in situ retort process may cause hydrologic impacts, the most significant being ground water contamination and possible transport of contaminants into unaffected areas. Although these impacts are site-specific, many of the techniques used to investigate each retort operation commonly will be the same. The U. S. Geological Survey has begun a study of hydrologic impacts in the area of an in situ retort near Rock Springs, Wyoming, as a means of refining and demonstrating these techniques. Geologic investigations include determining the areal extent and thickness of aquifers. Emphasis will be place on determining litho logic variations from geophysical logging. Hydrologic investigations include mapping of potentiometric surfaces, determining rates of ground-water discharge, and estimating aquifer properties by analytical techniques. Water-quality investigations include monitoring solute migration from the retort site and evaluating sampling techniques by standard statistical procedures. A ground water flow and solute transport model will be developed to predict future movement of the solute plume away from the retort.