If you're buying a home in Mankato, North Mankato, or anywhere in Southern Minnesota, you're in EPA Radon Zone 1 — the highest-risk zone in the country. About 40% of Minnesota homes test above the EPA action level of 4.0 pCi/L. The Minnesota Department of Health recommends testing every home, in every transaction, every two years.
Here's everything you need to know in plain English.
What is radon?
Radon is a colorless, odorless, tasteless radioactive gas. It comes from uranium decay in soil and rock — and Minnesota has plenty of both. The gas seeps up through foundation cracks, sump pits, plumbing penetrations, and concrete joints, and accumulates in the lowest level of the home.
Long-term exposure to elevated radon is the second leading cause of lung cancer after smoking — and the leading cause among non-smokers. The EPA estimates ~21,000 lung cancer deaths per year in the US are radon-related.
Why Mankato (and all of Minnesota) is high-risk
The geology under Southern Minnesota — limestone, shale, glacial till loaded with uranium-bearing minerals — is exactly the kind that produces radon. It's not anyone's fault. It's geology.
Local radon data:
- Blue Earth County (Mankato): ~42% of tested homes above 4.0 pCi/L
- Nicollet County (North Mankato, St. Peter): ~45%
- Le Sueur County: ~40%
- Brown County (New Ulm): ~38%
- Steele County (Owatonna): ~44%
Source: Minnesota Department of Health county-level radon test data.
How radon testing works (in your inspection)
I use a professional continuous radon monitor (CRM) — not the cheap charcoal canister you can buy at Menards. Here's why it matters:
- The CRM logs hourly readings for a minimum of 48 hours
- Tamper-resistant placement and chain of custody
- Same-day results when the test ends — not a 7-day lab wait
- Can detect anomalies like windows being opened during the test (which would skew a charcoal reading)
I drop the monitor at your home (or the home you're buying) at the start of the inspection, leave it for 48 hours in the lowest livable level, and pick it up. Results within minutes of pickup.
Cost: $200 standalone, $150 bundled with your inspection.
Reading the result
| Reading (pCi/L) | What it means |
|---|---|
| 0.0–1.9 | Low. Re-test every 2 years. |
| 2.0–3.9 | Moderate. EPA recommends considering mitigation. Re-test annually. |
| 4.0+ | EPA action level. Mitigate. |
What to do if the test is high
Don't panic. Mitigation is straightforward and effective.
The standard fix is a sub-slab depressurization (SSD) system: a contractor drills a small hole in your slab, runs PVC pipe up through the home (or outside it), and adds an inline fan that creates negative pressure under the slab. The radon gets pulled out before it can enter the house.
- Cost: $1,200–$2,500 for most Mankato-area homes
- Effectiveness: typically drops levels to under 2.0 pCi/L
- Time: 1 day to install
- Negotiation: if you're buying, request the seller pay for mitigation OR credit you the cost at closing. Most sellers agree — once the test is on paper, it has to be disclosed to the next buyer too.
FAQ
Is radon really that big a deal in Minnesota?
Can I just buy a charcoal kit at the store?
Does mitigation work?
Should I retest after mitigation?
Can radon enter through windows or doors?
Schedule a radon test (bundled with inspection saves $50)
— Lisa Meine, InterNACHI Certified Master Inspector & Continuous Radon Monitor Certified Operator