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February 14, 2023

PEMBROKE, N.H. More than half of New Hampshire is underlain by groundwater that has a 50% or higher probability of having elevated levels of radon, according to a recent study by the U.S. Geological Survey. The new USGS research also finds that a small portion of the state is underlain by groundwater with elevated concentrations of uranium.

This is the most comprehensive study to date and the first to create detailed statewide maps on the probability for any location in New Hampshire to have groundwater with either of those two radioactive elements.

Both radon and uranium can be a concern to human health in communities that have private wells. Approximately 40% of New Hampshire residents rely on private wells for uses such as drinking water, and those wells are supplied by groundwater.

The recent study represents groundwater and not necessarily drinking water, as groundwater can be filtered or treated prior to becoming drinking water. USGS scientists investigated where the substances, which are naturally occurring, may exist and in some cases be elevated above safe drinking water levels in accordance with standards identified by the state or the U.S. Environmental Protection Agency.

The EPA regulates public water supplies, but maintenance, testing and treatment of private water supplies are the responsibility of the homeowner. These findings highlight the importance of private well owners working with their local and state officials to determine the best way to test and, if necessary, treat their water supplies. Unless wells are tested, there’s no way to confirm the presence or absence of these contaminants. New Hampshire residents interested in testing their private wells for radon and uranium can find more information on the New Hampshire Department of Environmental Services website.

The USGS estimates that 55% of the state is more likely than not to have elevated radon in groundwater.

USGS map identifying the percent probability for any location in New Hampshire to have groundwater with radon concentrations greater than the state government’s standard of 2,000 picocuries per liter for drinking water.
USGS map identifying the percent probability for any location in New Hampshire to have groundwater with radon concentrations greater than the state government’s standard of 2,000 picocuries per liter for drinking water.

For uranium, 7% of the groundwater samples in the study were at elevated levels. Since it was found in a small part of New Hampshire, USGS scientists created a statewide probability estimate for lower, detectable levels – not necessarily at levels of concern. The USGS estimates that 76% of the state has a 50% or more probability for detectable concentrations of uranium in groundwater.

Much of the White Mountain region in the northcentral part of the state has relatively high probabilities for radon and uranium. Lower levels were found across parts of southern regions of the state.

“This is the first study to look across New Hampshire and estimate the likelihood of encountering radon or uranium in groundwater, helping identify who is living in an area with potential impacts to well water quality,” said Richard Moore, USGS hydrologist and the lead author of the new study.

“The process of where and how groundwater moves varies across the state and is influenced by factors such as regional geology,” continued Moore. “This study applies a comprehensive dataset to understand potential transportation of radon and uranium in different settings, allowing us to produce location-specific estimates for both elements.”

The New Hampshire state government’s standard for radon in drinking water is 2,000 picocuries per liter. The New Hampshire and EPA standard for uranium in drinking water is 30 micrograms per liter.

This assessment focused on identifying areas with radon or uranium in groundwater. The volume of groundwater underneath depends on the location.

This research builds upon a previous USGS study in 2004 on radon in the state’s groundwater. The recently published study looks at both radon and uranium, includes more samples, uses a new methodology for statistical analysis and assesses more factors within the groundwater system such as bedrock types.

The new study was done in cooperation with and received partial funding from the New Hampshire Department of Health and Human Services Environmental Public Health Tracking Program.

Learn more by reading an article by the USGS New England Water Science Center at

The study is available online at

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The USGS provides science for a changing world. Learn more at or follow us on Facebook @USGeologicalSurvey, YouTube @USGS, Instagram @USGS, or Twitter @USGS.  


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