Why radon levels vary across Vermont

Even so, the state’s geologists say everyone should test their home,⁠¹ and the Health Department says neighboring homes can have significantly different levels.⁠²

Where radon comes from

Radon forms naturally from the radioactive decay of uranium in rocks, surficial materials and soils over millions of years. It can move through fractures and layering in rock, or through connected pores in soil, and enter a home through the foundation.⁠¹ It can also get into well water if a well is drilled into or near rock that contains uranium.⁠³

What the bedrock data shows

Since 2009, the Vermont Geological Survey and the Health Department have studied how indoor radon relates to geology. Their 2019 report groups Vermont’s bedrock into zones of rock with similar age and geologic history, then matches them with 14,131 Health Department radon in air tests.⁠¹

From Plate 2 of Vermont Geological Survey Open File Report VG2019-2, rounded to one decimal place. One more zone, the Cretaceous granites, had a single test and is left out.⁠⁴ The percentages are shares of tests, not of all homes.

The survey describes the pattern this way: the Precambrian basement, Green Mountain and Champlain Valley zones cluster around the statewide average of 13%, the Taconic, Connecticut Valley and Devonian granite zones have higher percentages of elevated tests, and the Bronson Hill zone has a lower percentage. It adds that the maps give only a general indication.⁠¹ To see the zones on a map, open the bedrock view of the Health Department’s Radon Risk in Vermont maps.⁠²

What happens at the house

Geology is only part of it. The amount of radon in a home depends on many factors, including geology, the construction of the home, its mechanical systems and the way the home is used.⁠⁵ The Health Department lists:⁠²

• the concentration of radon in the soil, and how permeable the soil under the home is
• the structure and construction of the home
• the type, operation and maintenance of the heating, ventilation and air-conditioning system

The Northeast Kingdom

In an October 2025 conference presentation, the Health Department said 1 in 5 Northeast Kingdom homes has unsafe levels of radon, compared with 1 in 7 statewide. It linked the higher risk to geology, and said the region also has low testing rates and limited data.⁠⁶ The Department’s Northeast Kingdom outreach work covered Orleans, Caledonia and Essex counties.⁠⁶

The same presentation gives newer bedrock figures based on more tests than the 2019 report: 20.7% of 5,703 homes tested in the Connecticut Valley zone and 26% of 219 homes tested in the Devonian granites had elevated radon.⁠⁶ We cite it as a Health Department presentation hosted on the website of AARST (the American Association of Radon Scientists and Technologists), because we haven’t found the Northeast Kingdom figure on a Health Department page.

Test anyway

High levels of radon have been found in all types of homes in every area of Vermont.⁠⁵ A low-radon zone or town doesn’t mean a low-radon house, and a high one doesn’t mean yours is high. See how tests came out in your town, then test your own home.

Last reviewed October 17, 2026 · How we source facts