Radon Levels in Winona and Winona County
Minnesota is one of the highest radon states in the nation. The geology of the Driftless Area, where Winona sits, is a big part of why. This page covers the data and what it means for your house.
The numbers
| Measure | Value | Source |
|---|---|---|
| Minnesota homes above the 4.0 pCi/L action level | About 2 in 5 | MDH, January 2024 |
| Minnesota average indoor radon | ~4.2 pCi/L | MDH |
| U.S. average indoor radon | ~1.3 pCi/L | EPA |
| Winona County EPA radon zone | Zone 1, highest potential | EPA state map |
| U.S. lung cancer deaths from radon per year | ~21,000 | EPA / Surgeon General |
| U.S. homes above the action level | About 1 in 15 | EPA |
The Minnesota Department of Health publishes county-by-county test results on its interactive radon map. A county average describes the area, not your house. Two identical homes on the same Winona block can test very differently. The only number that matters for your family is the one from your own test.
Why this area tests high
Winona County lies in the Driftless Area, the corner of southeastern Minnesota the last glaciers never reached. There is no deep blanket of glacial till here. Instead you get thin soil over fractured Paleozoic bedrock, the limestone, dolomite, and sandstone that form the bluffs along the Mississippi. That rock and soil carry trace uranium, and uranium's decay chain produces radon gas. Karst features and rock fractures give the gas ready-made channels toward the surface. From there it enters a house through any pressure path it can find: slab cracks, floor drains, sump baskets, and utility penetrations.
Climate finishes the job. A Winona home spends most of October through April closed up and heated. Warm air rising out of the house pulls replacement air up from the soil. That stack effect turns the whole building into a gentle vacuum on the ground beneath it. It is why Minnesota's indoor average runs more than three times the national average, and why a winter test reads higher than a summer one.
What this means for Winona homes specifically
Much of Winona's housing predates any radon rule. Minnesota did not require radon-resistant construction until June 2009, so most homes in Winona, Goodview, Lewiston, St. Charles, and the surrounding townships were built with no radon protection. The older neighborhoods near the river carry full, lived-in basements, and a finished basement means someone breathes that lower-level air for hours a day. An open sump adds a direct soil-gas path. Both raise exposure.
Test the house. If it reads 4.0 pCi/L or higher, fix it. The EPA also suggests weighing a fix from 2.0 up. Costs and what drives them are in the Winona cost guide.