Call (609) 764-0850 to Get Connected
The EPA action level 4 pCi/L is the most-cited number in residential radon, and almost nobody who is not a radon professional understands what it actually means. It is not a safety threshold. It is not a regulatory limit in New Jersey. It is not a number below which radon is harmless. It is an EPA-recommended action point: the level at which the EPA tells homeowners “the cost of mitigation is reasonable compared to the long-term lung-cancer risk reduction.” Knowing what 4 pCi/L is and what it is not changes how Burlington County homeowners read their test results.
What pCi/L Even Means
“pCi/L” is picocuries per liter, a unit of radioactivity per volume of air. One picocurie is a trillionth of a curie. One picocurie per liter means that, in a single liter of air, there are radioactive disintegrations happening at a specific tiny rate. The unit measures how much radon is present and how much radioactive decay is occurring in the air your household breathes.
The relevant comparison: outdoor air across most of the continental US averages about 0.4 pCi/L. The EPA estimates the average indoor reading nationally is about 1.3 pCi/L. New Jersey averages slightly higher than the national mean because of regional geology. A 4.0 pCi/L reading is roughly 10x outdoor background and 3x the national indoor average. That is a meaningful elevation, but it is not an emergency number.
Why 4.0 And Not Some Other Number
The EPA chose 4.0 pCi/L in the 1980s based on cost-benefit analysis combining radon-induced lung cancer risk with the practical cost and feasibility of mitigation systems available at the time. The math behind it: at 4 pCi/L, sustained over decades of exposure, the lifetime risk of lung cancer is meaningfully elevated; mitigation systems can typically reduce home radon below this level for $1,500 to $3,000 installed; that cost-per-life-year-saved was within ranges the EPA considered reasonable for a public-health recommendation.
The EPA explicitly acknowledges that radon risk does not start at 4.0 pCi/L. Risk starts at any radon level above zero and rises proportionally. The agency suggests homeowners “consider mitigation” between 2.0 and 4.0 pCi/L, with mitigation strongly recommended at 4.0 and above. Some states (notably some New England states) have set their action levels lower for residential schools or for new construction.
How Burlington County Homes Actually Read
Test results are not evenly distributed across the EPA action level 4 pCi/L threshold. The Burlington County distribution looks roughly like this:
- About 35-45% of homes test below 2.0 pCi/L on a single 48-hour test
- About 35-40% test in the 2.0 to 4.0 pCi/L band (the “consider mitigation” zone)
- About 15-20% test in the 4.0 to 8.0 pCi/L band (clear mitigation candidates)
- About 3-7% test above 8.0 pCi/L (high-priority mitigation)
These distributions vary by zone. Western river-corridor homes skew higher; Pinelands homes skew lower on average but with tall outliers; suburban-ring homes cluster heavily in the 2.0 to 6.0 pCi/L band. Delaware River corridor radon, Pinelands radon, and Suburban radon cover the per-zone patterns.
What 4 pCi/L Means For A Real-Estate Transaction
NJ residential real-estate disclosure rules require any known radon test result to be shared with the buyer. The EPA action level 4 pCi/L is the de-facto threshold most NJ buyer’s inspectors use to flag a property for mitigation. A reading at or above 4.0 typically triggers one of three outcomes: seller installs mitigation before closing, buyer takes a credit and installs after closing, or the deal renegotiates. Below 4.0, mitigation is typically not contractually required, although some buyers ask for mitigation in the 2.0 to 4.0 band as additional leverage. Real-estate transaction radon details.
What surprises a lot of sellers: the buyer’s inspector test is a 48-hour short-term test, not a long-term annual-average measurement. A 48-hour reading taken during a cold snap with a tightly closed-up home can read meaningfully higher than the same home would average over a full year. Sellers occasionally challenge a 5.5 pCi/L buyer-inspector reading by arguing the 48-hour window was not representative. The EPA protocol still uses the short-term reading for transaction purposes.
What The Number Means For An Owner-Occupied Home
If you live in your home and your test comes back at 4.5 pCi/L, here is the practical math: lung-cancer risk from radon scales linearly with both concentration and exposure time. A 4.5 pCi/L number sustained for 30 years is meaningfully different from the same number sustained for 3 years. The EPA’s recommendation for owner-occupied homes is to mitigate at 4.0 and above, consider mitigation between 2.0 and 4.0 (especially if children sleep in the lowest level), and re-test every 2 years even after mitigation is in place.
For a 4.5 pCi/L home, mitigation drops the level below 2.0 pCi/L typically. The cost is usually $1,500 to $2,500 installed for a single-zone system. The fan runs about $7-10/month in electricity. Compared to the lifetime lung-cancer risk reduction, the math is favorable. How sub-slab depressurization works.
Common Misreadings Of The Number
- “Below 4.0 means safe.” Not what the EPA says. EPA uses language like “consider mitigation” between 2.0 and 4.0 pCi/L precisely because risk continues below the action level.
- “4.0 is a New Jersey legal limit.” Not for residential ownership. Some real-estate-transaction contractual structures and some lender programs treat 4.0 as a hard threshold but New Jersey does not impose a residential mitigation requirement.
- “My DIY kit said 3.8 pCi/L so I am fine.” A 3.8 reading is well within the variability of a single short-term test. Repeat the test or run a long-term alpha track for a more reliable annual-average number.
- “My basement reads 6.0 but I do not spend time there.” True, but the number above the basement is usually meaningfully elevated too. The basement reading often correlates with first-floor sleeping-area readings in the 2.5 to 4.0 range, which is also within the EPA “consider mitigation” zone.
If Your Number Is Above 4 pCi/L
The next step is a system design walk-through with a NJ-DEP-certified mitigation contractor. The system design depends on foundation type and zone; the EPA action level 4 pCi/L is the trigger but not the prescription. Contact a NJ-DEP-certified contractor in our network with the property address, your test number, and the foundation type.
By submitting this form you consent to be contacted by one or more NJ-DEP-certified radon mitigation contractors by phone, text, and email using the contact information you provide. Your information may be shared with our contractor partners to provide the requested quote. Reply STOP to any text to opt out. Standard message and data rates may apply. See our Privacy Policy and Disclaimer for details.
Related read: why a winter radon reading in Medford or Evesham is the one that counts.