In August 1984, Governor James R. Thompson signed legislation directed toward protection of groundwater from contamination. Public Act 83-1268 provides that the Illinois Dept. of Energy and Natural Resources, with cooperation from the Illinois Environmental Protection Agency and the Illinois Dept. of Public Health, will complete an assessment of current groundwater in Illinois by July 1, 1985. This document responds to the mandate of PA 83-1268 to develop a unified statewide groundwater protection plan. The plan identifies critical groundwaters that have been or are partially susceptible to contamination by hazardous substances.