Radon Level of 4 pCi/L or Higher: What to Do Next

There is no fully safe radon level — EPA is explicit that some risk exists at any concentration. What exists instead is a practical scale: 4.0 pCi/L and above is the EPA action level where mitigation is recommended; between 2.0 and 4.0 pCi/L, EPA recommends considering mitigation, especially for regularly occupied lower levels; below 2.0 pCi/L is the range well-designed mitigation systems typically achieve and is comparable to many homes’ baseline; and average outdoor air runs around 0.4 pCi/L. So the honest answer to "what is a safe level" is: as low as practically achievable — with 4.0 as the fix-it threshold, not a safety certificate.

No — it is an action level, not a line between safe and unsafe. EPA set 4.0 pCi/L as the level at which mitigation is recommended, while also noting that no radon level is risk-free and that mitigation is worth considering between 2.0 and 4.0 pCi/L. The action level exists because sub-slab mitigation systems reliably reduce homes below it, making it a practical fix threshold rather than a health guarantee. Two homes at 3.9 and 4.1 pCi/L have nearly identical risk; the difference is which one the guidance formally tells to mitigate. That is why occupancy matters in borderline decisions: a rarely entered basement at 3.5 pCi/L is a different situation from a basement bedroom at the same number.

Retest when the number is borderline or the first test is questionable; act directly when the number is high and the test was sound. A result near the action level from a single short-term test can move above or below 4.0 pCi/L on a second test, so a follow-up short-term test (or better, a long-term test) firms up the decision. A result several times the action level from a properly placed, properly conditioned test rarely changes category on retest — moving straight to mitigation planning is reasonable. If the result sits inside a real-estate deadline, weigh the days a retest costs against what it could change; often the practical answer is pricing mitigation now and letting the post-mitigation test serve as verification.

The fix goes by several names — radon mitigation, remediation, abatement, or removal all describe the same service — and it is almost always an active soil depressurization system: a suction point drilled through the slab (or set under a sealed crawlspace membrane), piping, and a continuously running in-line fan that pulls soil gas from under the foundation and vents it above the roofline. Installation is typically a one-day job that does not require excavation or major construction. The design varies with the foundation — sump-pit suction, multiple suction points for additions, or membrane systems for crawlspaces — which is why quotes should name the foundation areas they cover. In New Jersey, hired mitigation work must be performed by an NJDEP-certified professional; certification can be verified through the NJDEP Radon Program.

A post-mitigation radon test, run with the system operating, is the only real answer. The system’s manometer shows the fan is creating suction, but only a test shows the indoor radon number. The result should come back below 4.0 pCi/L — well-designed systems commonly land far lower — and the report should be kept with the system details in the home’s records, because future buyers and agents will ask for exactly that package. After that, periodic retesting (NJDEP guidance suggests about every two years, and after renovations or fan repairs) confirms the system keeps performing over its life.