My test came back above the EPA action level. Is that a real problem?

What pCi/L actually measures

A pCi/L (picocurie per liter) is a unit of radioactivity per volume of air. One picocurie is one trillionth of a curie. The number on your test is the average concentration of radon gas during the test window, in the room where the test sat.

Outdoor radon averages about 0.4 pCi/L. The U.S. national indoor estimate is around 1.3 pCi/L. The Minnesota state arithmetic mean (2014 to 2023) is 3.9 pCi/L. Half of tested Rochester homes sit above 3.2.

The three action lines

EPA action level: 4 pCi/L

The U.S. Environmental Protection Agency recommends taking action when a long-term test result lands at or above 4 pCi/L. The number is a practical line, set decades ago when home mitigation systems were less effective than they are now. Modern systems routinely bring homes well below 2 pCi/L, so the EPA line is more of a starting point than a stopping point.

WHO recommendation: 2.7 pCi/L

The World Health Organization recommends acting above 100 Bq/m³, which converts to roughly 2.7 pCi/L. The WHO number is more conservative than the EPA number, reflecting more recent risk modeling.

MDH guidance: 2 pCi/L

The Minnesota Department of Health recommends action when long-term test results exceed 2 pCi/L. About 68% of tested Olmsted County homes are at or above this threshold. Most of our installs target post-mitigation numbers below 2.

Short-term test versus long-term test

A short-term test runs 2 to 7 days, often with a charcoal kit or a continuous radon monitor. It is the right tool when you want a fast read or you are inside a real estate timeline. It also reflects whatever the weather and the house were doing during the test window.

A long-term test runs 90 days or more. It averages out the seasonal swing and gives a better picture of what the home actually breathes year-round. The EPA recommends a long-term test before any mitigation decision when there is no time pressure.

If your short-term result is below 4 pCi/L but above 2, MDH guidance suggests following up with a long-term test before deciding. If the short-term result is well above 4, the long-term result almost always confirms the picture.

What changes how you read the number

• Season. A winter short-term test will land higher than a summer one. Statewide, the difference is about 26%.
• Closed-house conditions. Windows and outside doors closed except for normal use, for 12 hours before and during the test, is the standard. Short-term tests that did not follow that protocol read lower than the home's actual number.
• Where the test sat. Tests in the basement read higher than tests on the main floor. The standard is to test the lowest livable level.
• Recent home changes. A new HVAC system, a renovation, or a new sump pit cover can shift the number from one test to the next.

What the next step looks like

For a number well above 4, the next step is a conversation about mitigation. For a number between 2 and 4, the next step is usually a follow-up test (long-term if there is no time pressure) and a decision about whether to mitigate. For a number below 2, the right move is to re-test in a few years and after any major home change.

We do free short-term tests across the Rochester area. If you have a number on a kit and want to talk through what it means for your specific home, that is what the phone is for.

Sources

• U.S. Environmental Protection Agency, Citizen's Guide to Radon.
• World Health Organization, WHO Handbook on Indoor Radon.
• Minnesota Department of Health, Indoor Air Unit, radon guidance.