Some areas of the country consistently produce higher indoor radon levels than others. But what makes a location high-risk? Understanding the geological and environmental factors behind radon hotspots can help you better assess your own home's risk.
Geology Is the Primary Factor
Radon originates from uranium in the earth's crust. Areas with naturally high uranium concentrations in the underlying rock and soil will produce more radon. The key geological formations associated with high radon risk include:
- Granite bedrock — Granite is naturally rich in uranium and radium, making granite-heavy regions some of the highest-risk areas in the world.
- Uranium-bearing shale — Certain shale formations contain elevated uranium levels that generate significant radon.
- Phosphate-rich soils — Phosphate deposits often contain uranium as a naturally occurring impurity.
- Glacial deposits — Areas covered by glaciers during the last ice age may have uranium-rich till and gravel deposits spread across wide regions.
High-Risk Regions in the United States
- The Reading Prong — A geological formation stretching through Pennsylvania, New Jersey, and New York with extremely high radon potential due to uranium-rich metamorphic rock.
- The Midwest — Iowa, Minnesota, Wisconsin, and surrounding states sit on glacial deposits with elevated uranium content.
- The Mountain West — Colorado, Wyoming, Montana, and Idaho have uranium-rich geology from ancient volcanic and sedimentary activity.
- Appalachian Region — Parts of Pennsylvania, Ohio, and West Virginia have high radon potential from shale and limestone formations.
Building Factors That Increase Risk
Even in lower-risk geological areas, certain building characteristics can concentrate radon to dangerous levels:
- Homes built on crawl spaces or slabs with poor sealing
- Buildings with sump pumps or open drainage systems
- Tightly sealed, energy-efficient homes with low air exchange rates
- Homes with well water from underground sources
No Area Is Completely Safe
Even in regions classified as low-risk, individual homes can have elevated radon levels due to local soil variations, building construction, and ventilation. The EPA emphasizes that every home should be tested, regardless of location.
Find Out Your Home's True Risk
Don't rely on regional averages. The GZAIR Radon Detector gives you the exact radon level in your specific home — continuous, real-time data that no map can provide.
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