CHAMPAIGN, Ill., 9/16/21: Walt Kelly, Illinois State Water Survey (ISWS) groundwater geochemist, answered questions about the findings of his recent study on radium levels in groundwater of the St. Peter Sandstone aquifer, with a study area in north-central Illinois. Radium levels are above the drinking water standard in many community water supply wells open to the aquifer.
What was the purpose of this study?
This study was part of a larger study undertaken to evaluate water supplies in the Middle Illinois Region. We were interested in what the water quality of the major aquifers was, and what the water chemistry could tell us about the evolution of groundwater in the deep aquifers.
Who was the report intended for?
The report was primarily for the scientific community, especially those interested in radioactivity in sandstone aquifers. But it was also intended for those communities and industries that use these aquifers, to help them understand and manage their water quality.
Why is it important to study radium in groundwater?
Drinking or cooking with water that contains too much radium can pose a hazard to human health. Drinking water is required to have no more than 5 picocuries per liter of radium. Being a radioactive element, it can also give us clues about what reactions are occurring within the aquifers and between them.
What are the environmental factors that affect the levels of radium in groundwater, particularly for north-central Illinois?
Radium is formed as uranium and thorium in the rock decay radioactively. There are many factors that can affect whether the radium remains in the water or is removed to solid phases, including the rock and water chemical characteristics.
What role do uranium and thorium play in the water levels of radium?
They are the “parents” of radium. They are formed as the uranium and thorium, which are found in the rocks, decay. The radium further decays, eventually forming non-radioactive lead. One form of radium also decays to radon, a carcinogenic gas. The more uranium and thorium in the rock, the more potential for radium and radon to be found in the groundwater.
What were the major results from the water sampling and analysis?
It’s been known for a long time that there are elevated radium levels in these aquifers. Our work has helped us understand the sources and transport of radium in this enormously complex hydrogeological and geochemical system. One thing we have been able to do is track the movement of Pleistocene meltwater into the aquifers and learn how they have mixed with brines and affected radium and uranium.
Where were the highest levels of radium in the study area and why?
The highest concentration we measured was 17.6 pCi/L. Earlier sampling north of our study region had many higher values, as high as 37 pCi/L. Differences in radium concentrations can be attributed to different amounts of the uranium and thorium and differences in solid and water chemistry that affect whether the radium remains in solution.
What are the implications of this study?
Communities using these aquifers will always have to deal with radium, because it is naturally occurring and is continually being produced. There may be several options, including various treatments or blending. One thing to remember in treatment is that the waste stream is radioactive, and its handling may be regulated by the Illinois Environmental Protection Agency.
What are the plans for future studies?
We have no concrete plans, but we are interested in looking more closely at rock cores to learn more about the association of uranium, thorium, and radium within the solid phase.
The report detailing the study, Hydrogeological and Geochemical Controls on Radium and Uranium in the St. Peter Sandstone Aquifer in the Middle Illinois Water Supply Planning Region, is available in the University of Illinois IDEALS depository. Co-authors include Samuel Panno, Keith Hackley, Daniel Hadley, and Devin Mannix.
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Media contact: Walt Kelly, 217-333-3729, wkelly@illinois.edu
news@prairie.illinois.edu
