Use of Geophysical Logs to Estimate Water Quality of Basal Pennsylvanian Sandstones, Southwestern Illinois

Fresh water is found at depths up to 1000 feet in basal Pennsylvanian sandstone aquifers along the southern margin of the Illinois Basin. These aquifers, though not highly productive, represent a significant potential source of ground water in a region of very limited ground‐water supplies. A pilot study was undertaken in southwestern Illinois using geophysical logs and limited hydrologic data to evaluate the potential of these aquifers. Water quality, porosity, and permeability were estimated from the geophysical logs; these data were then used in conjunction with data from aquifer performance tests to delineate zones of potable water. The data indicate that fresh‐water lenses extend basinward in sandstone paleochannels.