Elevated radium (Ra) and barium (Ba) concentrations are found in deep bedrock aquifers in parts of northern Illinois. There is rapid development occurring in the Chicago region, and many residents rely on groundwater for their drinking water. Radium and barium contamination is the most important water quality issue for public water suppliers in most of northern Illinois. Water from deep bedrock aquifers typically has to be treated or blended to reduce concentrations of these contaminants. In addition to health considerations, the presence of Ba can cause precipitation of barite (BaSO(sub 4)) in well bores, pumps, and discharge pipes, necessitating expensive maintenance. Because most wells drilled into deep bedrock aquifers are open to multiple aquifers, allowing waters to mix within the borehole, it is difficult to establish if one or more specific aquifers are primarily responsible for the elevated Ra and/or Ba. Previously it was suggested that the Ironton-Galesville aquifer may be the major source of contamination, based primarily on indirect evidence. The objective of this project was to identify and sample wells open only to individual deep bedrock aquifers in the Chicago region, and analyze for radioisotopes ((sup 226)Ra, (sup 228)Ra), Ba, and complete inorganic chemistry. A better understanding of the occurrence of Ra and Ba may help public water suppliers in siting future deep bedrock wells.
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