Geologic sources of radium to municipal wells in Wisconsin
Matthew Ginder-Vogel, University of Wisconsin-Madison
Madeline Gotkowitz, Wisconsin Geological and Natural History Survey
Radium commonly occurs in groundwater obtained from the Midwestern, Cambrian-Ordovician aquifer system at activities (a measure of concentration) close to or exceeding the U.S. Environmental Protection Agency’s Maximum Contaminant Level (MCL) of 5 pCi/L for combined 226Ra and 228Ra. Many communities in Wisconsin and the north-central United States rely on these regionally extensive, dolomitic and sandstone aquifers for their principal source of drinking water. A recent U.S. Geological Survey study of radium occurrence and geochemistry found this aquifer in the Midcontinent and Ozark Plateau region has the highest frequency of Ra occurrence among the 15 major aquifer systems in the country. The 95 public water systems in Wisconsin with Ra levels exceeding the MCL have adopted various strategies to bring their systems into compliance. These strategies include well reconstruction, water treatment by ion exchange or blending, and/or abandonment of groundwater systems in favor of surface water sources. However, the source of Ra contamination to the groundwater has not been identified: therefore it is difficult to plan municipal well construction to avoid Ra contaminated water. The proposed research project is designed to address this gap in knowledge by developing a quantitative relationship between sediment and aqueous geochemistry and the concentration of Ra in groundwater.