If you've just gotten a radon test result above 4 pCi/L, the next question is almost always the same: how does radon mitigation actually work? Here's the direct answer, followed by the full process breakdown so you know exactly what a contractor should be doing in your basement or crawlspace.
How does radon mitigation work?
Radon mitigation works by installing an active soil depressurization (ASD) system — a sealed pipe connected to a fan that pulls radon gas from beneath the foundation and vents it above the roofline before it ever enters your living space. A hole is cut through the concrete slab, a suction pit is dug into the sub-slab gravel, PVC pipe is routed up through the house (or along an exterior wall), and a continuously-running in-line fan creates negative pressure under the slab. This depressurized zone intercepts radon before it can seep up through the floor, cracks, or sump pit.
What actually happens during ASD installation
Active soil depressurization is the same core method used in roughly 90%+ of U.S. radon mitigation installs, including nearly all Minnesota basements and slab-on-grade homes. The steps a licensed installer follows are fairly consistent:
- Diagnostic evaluation: The mitigator identifies the best suction point — usually the sump basket if one exists, since it's already a direct path to the aggregate below the slab.
- Suction pit: If no sump is available, they cut a 4–6 inch hole in the slab and hand-dig a small pit in the sub-slab material to give the system more surface area to pull air from.
- Piping: Schedule 40 PVC pipe runs from that point through the basement, up through a closet, garage, or exterior wall, and terminates at least 10 feet above grade and away from windows or eaves, per AARST/ANSI radon mitigation standards.
- Fan installation: An inline radon fan (typically mounted in the attic or on an exterior wall, never inside a livable space) runs continuously, drawing roughly the same wattage as a couple of incandescent light bulbs — most residential radon fans use around 40–100 watts.
- Sealing: Foundation cracks, the sump lid, and slab penetrations are sealed with polyurethane caulk so the system's vacuum isn't leaking room air instead of soil gas.
- Verification: A U-tube manometer is installed to visually confirm the system is maintaining vacuum, and a follow-up radon test is recommended within 30 days of activation to confirm the reduction.
Why Minnesota homes need this more than most states
Minnesota consistently ranks among the states with the highest average indoor radon levels in the country. That's largely because of glacial soil deposits rich in uranium-bearing minerals across much of the state, combined with basements built directly on or below grade — the most common foundation style here. The Minnesota Department of Health has long recommended every home be tested, regardless of age or foundation type, because radon levels can vary significantly between two houses on the same block depending on soil permeability and foundation cracking.
One detail most competitors skip: Minnesota winters actually make radon readings higher on average, because homes are sealed tight against the cold and the stack effect (warm indoor air rising and pulling soil gas in through the lowest level) is stronger. If you tested in summer with windows open, a winter re-test is worth doing before ruling out mitigation.
What radon levels are actually dangerous?
The EPA's action level is 4 picocuries per liter (pCi/L) — at or above that, the EPA recommends mitigation. The EPA also notes there is no truly "safe" level of radon exposure, since it's a radioactive gas linked to lung cancer risk that increases with both concentration and duration of exposure, but 4 pCi/L is the practical threshold used nationwide for deciding when to act. Between 2 and 4 pCi/L, the EPA still suggests homeowners consider mitigation, especially in a state with Minnesota's soil profile.
January is designated National Radon Action Month by the EPA — a good annual reminder to test or re-test, since radon levels can shift year to year as soil, weather, and home sealing change.
FAQ
What is active soil depressurization?
Active soil depressurization (ASD) is the standard radon mitigation method that uses a fan-powered vent pipe to create negative pressure beneath a home's foundation, drawing radon gas from the soil and expelling it outdoors above the roofline instead of letting it enter the house through slab cracks or the sump.
How much exposure to radon is dangerous?
There's no exposure-free threshold, but the EPA sets 4 pCi/L as the action level for mitigation, since long-term exposure at or above that concentration is associated with meaningfully increased lung cancer risk. Risk is cumulative — it depends on both the concentration measured and how many hours per day you spend in that space, so a bedroom or finished basement matters more than a rarely-used utility room.
Does a radon mitigation system need maintenance?
Yes — the fan should be checked visually via the manometer periodically, and most radon fans have a functional lifespan of roughly 5–10 years before needing replacement. A failed fan won't necessarily be obvious without checking the manometer gauge, so an annual glance at it is worth the two minutes.
This article is educational and general in nature and is not a substitute for an on-site radon test, a licensed mitigation contractor's evaluation, or guidance from the Minnesota Department of Health. Radon test results, mitigation requirements, and permitting rules can vary by municipality — check your local building department before installation.