Principal Aquifers Can Contribute Radium to Sources of
Drinking Water Under Certain Geochemical Conditions
By Zoltan Szabo, Jeffrey M. Fischer, and Tracy Connell Hancock
What are the most important factors affecting dissolved radium concentrations in principal aquifers used for drinking
water in the United States? Study results reveal where radium was detected and how rock type and chemical processes
control radium occurrence. Knowledge of the geochemical conditions may help water-resource managers anticipate
where radium may be elevated in groundwater and minimize exposure to radium, which contributes to cancer risk.
Summary of Major Findings
- Concentrations of radium in principal
aquifers used for drinking water
throughout the United States generally
were below 5 picocuries per liter
(pCi/L), the U.S. Environmental
Protection Agency (USEPA) maximum
contaminant level (MCL) for combined
radium—radium-226 (Ra-226) plus
radium-228 (Ra-228)—in public water
supplies. About 3 percent of sampled
wells had combined radium concentrations
greater than the MCL.
- Elevated concentrations of combined
radium were more common in groundwater
in the eastern and central United
States than in other regions of the
Nation. About 98 percent of the wells
that contained combined radium at
concentrations greater than the MCL
were east of the High Plains.
- The highest concentrations of combined
radium were in the Mid-Continent and
Ozark Plateau Cambro-Ordovician aquifer
system and the Northern Atlantic Coastal
Plain aquifer system. More than 20 percent
of sampled wells in these aquifers had
combined radium concentrations that
were greater than or equal to the MCL.
- Concentrations of Ra-226 correlated
with those of Ra-228. Radium-226 and
Ra-228 occur most frequently together
in unconsolidated sand aquifers, and
their presence is strongly linked to
- Three common geochemical factors
are associated with the highest radium
concentrations in groundwater:
(1) oxygen-poor water, (2) acidic
conditions (low pH), and (3) high
concentrations of dissolved solids.
First posted February 7, 2012
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Szabo, Zoltan, Fischer, J.M., and Hancock, T.C., 2012, Principal aquifers can contribute radium to sources of
drinking water under certain geochemical conditions: U.S. Geological Survey Fact Sheet 2010–3113, 6 p., available at https://pubs.usgs.gov/fs/2010/3113/.