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Scientists Home in on Causes of High Radium Levels in Key Midwestern Aquifer

Oxygen levels, dissolved minerals among factors responsible for high concentrations of radium in untreated water from aquifer that underlies six states

U.S. Geological Survey scientists have shed new light on processes that happen deep underground.

These processes — which cause radium to leach from aquifer rocks into groundwater — are responsible for high concentrations of naturally occurring radium in groundwater from the Cambrian-Ordovician aquifer. This aquifer provides more than 630 million gallons of water a day for public supply to parts of Illinois, Iowa, Missouri, Michigan, Minnesota, and Wisconsin.

A newly published USGS study helps explain how radium isotopes 224, 226, and 228 make their way into water in the Cambrian-Ordovician aquifer and where concentrations are highest. The study, part of the USGS National Water Quality Assessment Project, reports that water that was recharged into the aquifer long ago, that contains greater amounts of dissolved minerals, and that is low in dissolved oxygen is more likely to leach radium from the surrounding rock.

The groundwater tested came from public supply wells, before treatment and distribution. Radium can be removed from drinking water through treatment, thereby limiting the health risks it poses. Private wells were not tested during this study, however, more than half a million people get their drinking water from private wells that tap the Cambrian-Ordovician aquifer. These homeowners might consider having their water tested for radium.

For additional information on the article, contact Paul Stackelberg,


Stackelberg, P.E., Szabo, Z., and Jurgens, B. Radium mobility and the age of groundwater in public-drinking- water supplies from the Cambrian-Ordovician aquifer system, north-central USA. Sci. Total Environ. 2017.

Explore USGS interactive maps— Decadal Trends in the Quality of the Nation’s Groundwater:


Map of trends in Chloride concentrations in the U.S.

Untreated groundwater from public-supply wells in the confined region of the Cambrian-Ordovician aquifer was more likely than wells in the unconfined region to contain combined radium at levels above the Maximum Contaminant Level (MCL) for drinking water of 5 picocuries per liter. Low concentrations of dissolved oxygen and high concentrations of dissolved minerals are among the factors that cause radium to leach from the aquifer rocks into the groundwater.

The Cambrian-Ordovician aquifer is a source of drinking water
for residents of Minneapolis and other cities in the upper

The Cambrian-Ordovician aquifer is a source of drinking water for residents of Minneapolis and other cities in the upper Midwest.


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Page Last Modified: Wednesday, 13-Dec-2017 12:54:17 EST