The EPA sorts every U.S. county into three radon zones by geology and measured data. Dane County sits in Zone 1 — predicted average indoor levels above the 4 pCi/L action level. Here is how to use that information without either panicking or ignoring it.
What the zone actually measures
It is a prediction about averages, built from soil chemistry, aerial radioactivity surveys, and historical test results. It says testing in Madison is a when-not-if item — it says nothing certain about your specific foundation.
Wisconsin's own health department data agrees with the federal map: statewide, high tests are routine, and Dane County contributes its share.
Why neighbors test differently
Two houses on the same Verona cul-de-sac can read 2 and 14. Entry depends on the gravel and soil under each footprint, the cracks in each slab, whether the sump is sealed, and how each house breathes. The zone cannot see any of that; a $25 test can.
Local wrinkles worth knowing
Madison's mix skews the odds in specific ways: older near-campus homes with stone or block foundations leak soil gas generously, while newer tight construction in the suburbs holds whatever enters. Both patterns produce high readings — by different routes.
Finished basements, near-universal in newer Dane County builds, multiply exposure hours rather than concentration. The number matters more when someone sleeps down there.
Using the map correctly
Let Zone 1 set your default: test at purchase, test after finishing a basement, retest every two years. Treat an existing mitigation system on a listing as a solved problem with paperwork, not a defect. And never let a neighbor's low test — or high one — stand in for your own.
How to act on Zone 1
Test now if you never have; test in winter for the honest reading; retest every two years and after any project that touches the foundation or airflow. If the result is high, mitigate once and verify — the zone stops being your problem the day the manometer shows vacuum.
The map's job was only ever to get you to take the twenty-dollar step. Everything after that is specific to your house.
