Radon: The Invisible Risk in Every Basement
Radioactive, odorless, and the second-leading cause of lung cancer in the United States.
What radon is
Radon is a naturally occurring radioactive gas produced by the decay of uranium in rocks and soil. Uranium is present in trace amounts almost everywhere — and as it decays over millions of years, it produces radon, which seeps up through soil and into the buildings above.
Outdoors, radon disperses harmlessly. Indoors, it can accumulate to concentrations that significantly increase lung cancer risk. The EPA estimates that radon causes about 21,000 lung cancer deaths per year in the U.S. — more than secondhand smoke, more than drunk driving accidents.
Why basements (and ground floors)
Radon enters homes through cracks in the foundation, gaps around pipes, sump pits, drains, and any direct opening between the soil and the indoor air. Basements and slab-on-grade ground floors have the most surface area in contact with the soil, which is why they tend to have the highest levels.
But "my house doesn't have a basement" is not a reason to skip testing. Slab homes, crawl-space homes, and even upper floors can have elevated radon.
The numbers
EPA action level: 4 picocuries per liter (pCi/L). At or above this level, the EPA recommends mitigation.
EPA "consider mitigation" level: 2-4 pCi/L. The agency notes that no level is safe and recommends action below 4 pCi/L if practical.
WHO action level: 100 Bq/m³ (about 2.7 pCi/L).
Average indoor U.S. level: about 1.3 pCi/L.
Short-term vs. long-term tests
Short-term tests (2 to 90 days) are the fastest way to find out if you have a problem. EPA recommends short-term testing as a first step for almost everyone. Results vary day-to-day, so a short test gives you a snapshot.
Long-term tests (90+ days, often 12 months) give a true annual average. EPA recommends a long-term test if a short-term test is between 2 and 4 pCi/L, or after mitigation to confirm the system is working.
Best practice: a short-term test first. If it's above 4 pCi/L, mitigate. If it's between 2 and 4, follow up with a long-term test.
Radon in water
If your home is on a private well, radon can enter your water as well as your air. When you shower, run the dishwasher, or do laundry, radon escapes from the water into the air — adding to your indoor exposure.
There is no federal MCL for radon in water yet, but the EPA's proposed standard is 4,000 pCi/L if your state requires multi-media radon programs, or 300 pCi/L otherwise. Well water radon should be tested separately from indoor air radon.
Mitigation
Active soil depressurization (ASD) is the standard mitigation: a fan and vent pipe pull radon from beneath the foundation and exhaust it above the roofline before it can enter the home. Typical cost: $1,000-$2,500. Effective: usually drops levels by 50-99%.
Sealing cracks alone is not sufficient — it can reduce levels somewhat, but it doesn't address the pressure differential that pulls radon in.
For radon in well water: aeration systems are the most effective; granular activated carbon also works for low-to-moderate levels.
After installing any mitigation system, retest within 30 days to confirm it's working. Then retest every 2 years.
If you've never tested for radon
Do a short-term test now. They take 2-7 days and cost less than $50. The EPA recommends it for every home in every state, regardless of whether your neighbors have tested.
General education, not advice. This article is for information only — not medical or legal advice. Lab results should be interpreted in the context of your specific home and situation. See our full Disclaimer.