EPA radon zone by city
| City | County | EPA zone | Predicted county average |
|---|---|---|---|
| Albuquerque | Bernalillo County, NM | Zone 1 | above 4 pCi/L |
| Boston | Middlesex County, MA | Zone 1 | above 4 pCi/L |
| Cincinnati | Hamilton County, OH | Zone 1 | above 4 pCi/L |
| Colorado Springs | El Paso County, CO | Zone 1 | above 4 pCi/L |
| Columbus | Franklin County, OH | Zone 1 | above 4 pCi/L |
| Denver | Denver County, CO | Zone 1 | above 4 pCi/L |
| Indianapolis | Marion County, IN | Zone 1 | above 4 pCi/L |
| Kansas City | Jackson County, MO | Zone 1 | above 4 pCi/L |
| Louisville | Jefferson County, KY | Zone 1 | above 4 pCi/L |
| Madison | Dane County, WI | Zone 1 | above 4 pCi/L |
| Minneapolis | Hennepin County, MN | Zone 1 | above 4 pCi/L |
| Nashville | Davidson County, TN | Zone 1 | above 4 pCi/L |
| Omaha | Douglas County, NE | Zone 1 | above 4 pCi/L |
| Pittsburgh | Allegheny County, PA | Zone 1 | above 4 pCi/L |
| Spokane | Spokane County, WA | Zone 1 | above 4 pCi/L |
| Boise | Ada County, ID | Zone 2 | 2–4 pCi/L |
| Chicago | Cook County, IL | Zone 2 | 2–4 pCi/L |
| Cleveland | Cuyahoga County, OH | Zone 2 | 2–4 pCi/L |
| Milwaukee | Milwaukee County, WI | Zone 2 | 2–4 pCi/L |
| Phoenix | Maricopa County, AZ | Zone 2 | 2–4 pCi/L |
| Portland | Multnomah County, OR | Zone 2 | 2–4 pCi/L |
| Charlotte | Mecklenburg County, NC | Zone 3 | below 2 pCi/L |
| Detroit | Wayne County, MI | Zone 3 | below 2 pCi/L |
| Philadelphia | Philadelphia County, PA | Zone 3 | below 2 pCi/L |
| San Diego | San Diego County, CA | Zone 3 | below 2 pCi/L |
| Seattle | King County, WA | Zone 3 | below 2 pCi/L |
Chicago and Pittsburgh link to full local guides. For any other U.S. county, look it up on the EPA map.
What the zones mean
Zone 1 · Highest potential
The EPA predicts a county-average indoor radon level above 4 pCi/L.
Zone 2 · Moderate potential
The EPA predicts a county-average indoor radon level 2–4 pCi/L.
Zone 3 · Low potential
The EPA predicts a county-average indoor radon level below 2 pCi/L. Lower potential is not no potential: homes in Zone 3 counties can and do test above 4 pCi/L.
Your zone doesn't replace a test
Radon depends on the soil and the construction of each house, so two neighbors can get very different results. The EPA's action level is 4 pCi/L, and it recommends considering a fix between 2 and 4 pCi/L. A short-term test kit costs around $15–30; a continuous monitor shows how levels change over weeks and seasons.