Take a breath — you’re in good company
A high radon test feels like bad news about your house. Around Sioux Falls, it’s closer to a routine finding. Eastern South Dakota sits in the EPA’s highest-potential radon zone, and a large share of the homes tested in this state read at or above the action level. The published numbers are collected at radon levels in your area, and they’ll make you feel less singled out.
Here’s what your result does not mean. It doesn’t mean your house is defective, or that someone built it wrong, or that you’ve done something to cause it. Radon rises out of the soil under every home. Some soil gives off more, some houses hold more of it, and the only way anyone finds out is the way you just did.
It also doesn’t mean anything needs to happen today. Radon risk is about long-term exposure, measured in years. This is not a gas leak, not a same-day emergency. You have time to confirm the number, understand it, and fix it properly.
And it is fixable, reliably, without tearing up the house. Mitigation is established work with a verifiable result, and most of this page is about what that path looks like. The short version: understand your number, confirm it if it’s close to the line, fix it if it isn’t, and prove the fix with a retest.
That’s the whole map. The rest is detail.
Where your number sits, per EPA guidance
Under 2 pCi/L
- What EPA guidance says
- Low for an occupied home
- A sensible next move
- Retest in a few years
2 to 4 pCi/L
- What EPA guidance says
- Consider fixing the home
- A sensible next move
- Confirm, then decide
4 to 8 pCi/L
- What EPA guidance says
- At the action level; fix
- A sensible next move
- Confirm if time allows, then mitigate
8 pCi/L and up
- What EPA guidance says
- Well past the action level
- A sensible next move
- Plan mitigation now, verify by retest
| Your result | What EPA guidance says | A sensible next move |
|---|---|---|
| Under 2 pCi/L | Low for an occupied home | Retest in a few years |
| 2 to 4 pCi/L | Consider fixing the home | Confirm, then decide |
| 4 to 8 pCi/L | At the action level; fix | Confirm if time allows, then mitigate |
| 8 pCi/L and up | Well past the action level | Plan mitigation now, verify by retest |
Radon is measured in picocuries per liter (pCi/L). The EPA action level is 4 pCi/L.
What the number actually means
Radon is measured in picocuries per liter, written pCi/L. The EPA’s action level is 4. At or above that, guidance says fix the home. Between 2 and 4, guidance says consider fixing it. Reduction there is still worthwhile, just less urgent. What the numbers mean unpacks the whole scale if you want the longer version.
One thing worth knowing before you stare too hard at your exact digits: radon levels move. Season, weather, and how the house was used during the test all push the reading around. A basement that reads 5.1 in January might read 3.4 in June. Neither number is a lie. Both are snapshots of a moving target, which is why guidance is built around ranges, not decimals.
That’s also why a follow-up test sometimes makes sense before spending money. If a short-term screen came back near the line, say 4 to 8, a second test (or better, a long-term test) tells you whether the first reading was the house’s honest average. If your result came from a multi-day monitored test, or the number is well past 8, confirmation adds less. The picture is already clear enough to act on.
A deadline changes the calculus. If the test happened because a home is changing hands, there’s usually no room for a 90-day follow-up, and a monitored transaction test is solid enough to move straight to reducing the level. More on that below.
Have the number in hand? An estimate turns it into a plan
What fixing it involves
The fix is a mitigation system, and the concept fits in a sentence: give the gas an easier way out than through your floor.
In practice, a hole gets cored through the basement slab and a shallow pit hollowed out beneath it. A PVC pipe runs from that pit up through the house, often through a garage or utility chase, sometimes up an outside wall, to a vent above the roofline. An inline fan runs continuously, pulling soil gas from under the slab and pushing it out above the roof, where it disperses into open air. A small u-tube gauge on the pipe shows the system is holding suction. Homes over crawlspaces, or with sump pits, get variations on the same idea. The full component-by-component tour, with the reasoning behind each part, is in how radon mitigation works.
Before any of that, someone looks at the house. Foundation type, slab sections, sump pit, finished rooms: the layout decides where the system pulls from and where the pipe can run. That assessment is where a real scope comes from. Treat any firm design quoted sight-unseen with suspicion.
Now the honesty clause, because this is where marketing usually oversells. A properly designed system is built to bring the home below the action level, and most land well below it. But nobody can promise your basement a specific number in advance — soil doesn’t sign contracts. What a good installer promises instead is verification: a follow-up test after the system is running. If the number isn’t under the action level, the system gets adjusted until it is. The retest is the guarantee, in the only form an honest trade can offer one.
If you’re under contract
A high result mid-deal compresses the timeline. It doesn’t change the fix.
Elevated radon is one of the most routinely resolved inspection findings in a home sale. The parties negotiate who handles it (a seller-paid install, a credit at closing, occasionally a shared cost) and the system goes in on the deal’s schedule. The verification retest produces the document everyone actually wants: a written number below the action level, attached to the file.
What deadlines punish is delay, not the problem itself. The confirm-with-a-long-term-test step usually gets skipped, sensibly, because a monitored 48-hour transaction test is already trustworthy. If that’s your situation, radon in a home sale walks through the sequencing, who typically pays, and how the paperwork lands, all at deal speed.