Investigating sources of salinity associated with Ra and Sr in the Cambrian-Ordovician aquifer system of eastern WI

The Midwestern Cambrian-Ordovician aquifer system, an important drinking water source, contains elevated levels of radium (Ra) and strontium (Sr) in many Wisconsin municipalities. Radium is regulated in drinking water by the U.S. Environmental Protection Agency (EPA) due to its association with bone disease. Strontium is on the U.S. EPA Contaminant Candidate List 3 and may be regulated in the future. Known health effects of Sr consumption include tooth mottling and “strontium rickets,” a musculoskeletal disease. These contaminants exhibit similar chemical behavior and are typically associated with reducing conditions and old, high-salinity groundwater (i.e., groundwater elevated total dissolved solids). Reducing aquifer conditions can be induced by confining units or local stagnation zones. The sources of salinity are not well constrained, and can vary throughout the aquifer system.

The goal of the proposed study is to identify the water-rock interactions and sources of salinity within the Cambrian-Ordovician aquifer system (COAS) of eastern Wisconsin associated with elevated Ra and Sr, and develop an understanding of the transport of these contaminants to municipal wells. We plan to achieve this goal by studying elevated Ra and Sr in Fond du Lac County, and collaborating with the Fond du Lac Water Utility, homeowners and non-community drinking water systems, UW Biotechnology Center, and the Wisconsin State Laboratory of Hygiene. Our objectives include: 1) Identify wells in Fond du Lac and geochemically characterize groundwater elevated in Ra and Sr, 2) Determine water-rock interactions and sources of salinity within the aquifer system using a suite of isotopic tracers (δD, δ18O, δ 34S – SO4 2- , 234U/238U, 87Sr/86Sr), and 3) Model groundwater flow and contaminant transport to municipal wells. Results of the study will be shared with state water utilities and regulators, homeowners, and noncommunity drinking water systems, and will guide strategies for minimizing Ra and Sr uptake by municipal wells.