If you've tested your home and seen a number next to "pCi/L," you're probably wondering whether it's actually bad — and Iowa is a confusing place to ask that question, because the state's radon readings run higher than almost anywhere else in the country. Here's what the numbers mean and how the fix, active soil depressurization (ASD), actually works underneath your slab.
What Radon Level Is Considered Dangerous in Iowa Homes?
The U.S. Environmental Protection Agency's action level of 4 picocuries per liter (pCi/L) is the threshold at which mitigation is recommended for any home in the country, including Iowa. Because Iowa's glacial soils release radon gas at unusually high rates, it's common for homes here to test at 8 pCi/L or higher — double the national trigger point.
The EPA's own guidance, A Citizen's Guide to Radon (epa.gov/radon), notes there's technically no known "safe" level of radon exposure, since it's a radioactive gas linked to lung cancer at any concentration. The 4 pCi/L line is a risk-versus-cost benchmark, not a safety cliff — a reading of 3.8 pCi/L isn't meaningfully safer than 4.2 pCi/L, it's just below the line where the EPA formally recommends action.
How Do Iowa's Radon Levels Compare to the Rest of the Country?
Iowa's statewide average indoor radon level runs well above the national average, largely because the entire state sits on glacially deposited soil rich in uranium-bearing minerals. That geology — not construction quality — is the primary reason homes in Des Moines, Ankeny, Altoona, Urbandale, Cedar Rapids, and small towns across the state routinely test high regardless of age or foundation type.
During the last continental glaciation, ice sheets ground up granite and other uranium-bearing rock from farther north and deposited it as loess and till across nearly the entire state. As uranium in that soil naturally decays, it produces radon gas, which is drawn into homes through foundation cracks, sump pits, and utility penetrations — especially during Iowa's cold months, when furnaces and stack effect pull more air (and soil gas) up through the house.
What Is Active Soil Depressurization and How Does It Lower Radon?
Active soil depressurization (ASD) is the standard radon mitigation method: a fan-powered pipe system installed through the slab or foundation that continuously pulls soil gas from beneath the home and vents it above the roofline before it can seep into living space. It's sometimes called active sub-slab depressurization or active subslab suction — all three terms describe the same system.
In a typical Iowa installation, the licensed operators in our network core a hole through the basement or garage slab, insert PVC pipe down into the gravel or soil layer, and route it vertically through a closet, utility chase, or exterior wall to a termination point above the roof edge. An inline fan — usually mounted in the attic or on the exterior — runs continuously to maintain negative pressure under the slab. A small U-tube manometer near the pipe shows at a glance whether the fan is still creating suction, which is how a homeowner can visually confirm the system is working between tests.
Where the pipe goes matters
Placement isn't arbitrary — sealed sump pits, French drains, and any known soil gas entry points typically get tied into the same suction field so one fan can depressurize the whole slab rather than just one corner of the basement.
How Long Does It Take for an ASD System to Reduce Radon Levels?
Most active soil depressurization systems drop indoor radon significantly within the first 24 hours of running, since the fan immediately starts reversing the pressure difference that was pulling soil gas indoors. Full confirmation, however, requires a follow-up test rather than guesswork.
Best practice — consistent with EPA testing protocols — is to wait at least 24 hours after activation before retesting, and many operators recommend a short-term retest between 2 and 30 days post-installation to confirm the reading has stabilized below 4 pCi/L. Because radon fluctuates with weather, soil moisture, and season, a single-day reading right after installation isn't the whole picture; a home tested in humid August conditions can read differently than the same home during a dry Iowa winter.
Do Iowa Radon Mitigation Systems Need Ongoing Maintenance?
Yes — an ASD system is mechanical, and the fan is the part that eventually fails. Most radon fans are rated for roughly 5 to 15 years of continuous operation, and a failed fan means the system stops protecting the home even though the pipe is still in place. Checking the manometer periodically, and after any storm or power outage, is the easiest way to catch a dead fan early.
System design and installation in the mitigation industry generally follows ANSI/AARST standards for soil gas mitigation in existing homes, which cover things like pipe sizing, fan placement, and labeling requirements so a future homeowner or inspector can identify the system. Iowa's Department of Health and Human Services also maintains program oversight for radon measurement and mitigation professionals operating in the state. Retesting every two years, or any time you renovate the foundation, add a room, or notice the manometer reading has changed, keeps the system honest over its lifespan.
This article is educational and does not replace a current radon test or an in-home evaluation. Radon levels vary by property, season, and soil conditions even within the same neighborhood; rules for testing devices, contractor certification, and retesting intervals can vary by municipality, so confirm specifics with a licensed operator or your local health department before making a mitigation decision.