Radon Levels in Bismarck–Mandan: County Data
North Dakota is one of only two states with every county in EPA Zone 1. Here are the county figures from the state's survey, the geology behind them and what they mean today.
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The numbers by county
The ND Department of Health and EPA tested 1,596 homes in winter 1987–88. In Burleigh County 101 homes averaged 4.9 pCi/L, with a median of 3.8 and 47% above 4. In Morton County 99 homes averaged 5.6, with a median of 4.4 and 53% above 4.
Neighboring counties ran higher: Oliver 84%, Mercer 72%, McLean 71%, Grant 61%, Emmons 53% and Kidder 50%. This is the only county-level survey published, so no one has a newer county figure.
Why the ground here makes radon
North Dakota's glacial soils come largely from Cretaceous shales with above-average uranium. Dry clay cracks and lets soil gas travel. The highest reading in the 1987–88 survey was 184 pCi/L somewhere in the state.
Statewide, the DEQ says 63% of homes are above the 4.0 pCi/L action level (January 2026 release).
Health, in plain terms
The EPA links radon to about 21,000 US lung-cancer deaths a year and calls it the number one cause among non-smokers. The ND DEQ notes that radon-induced lung cancer typically develops 5–25 years after exposure.
North Dakota's lung cancer rate is 54.3 new cases per 100,000, against 52.8 nationally (American Lung Association, Nov 2025).
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Frequently asked questions
Is Bismarck high in radon?
Burleigh County is Zone 1 and 47% of 101 tested homes in 1987–88 were over 4 pCi/L. Test your own house, since levels vary house to house.
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