Radon in Ohio: Why Newark Has the Highest Radon in the Country

Newark, Ohio sits at roughly 4.2 pCi/L average indoor radon — nearly double the EPA’s action level of 4.0 pCi/L and more than three times the national indoor average of 1.3 pCi/L. That makes it one of the highest-radon cities in the entire United States, and yet most people buying homes there have no idea until a test kit comes back with a number that stops them cold. The real problem isn’t that Newark has high radon — it’s that the reason why it’s so high is almost never explained, which means homeowners make bad decisions about testing, timing, and mitigation based on incomplete information.

Why Does Newark, Ohio Have Such Extreme Radon Levels?

The short answer is geology, but that word gets thrown around so loosely that it stops meaning anything. What’s actually happening beneath Newark is specific: the city sits directly on glacial till deposits laid down during the last ice age, and that till is packed with uranium-bearing soils and rock fragments scraped from the granite-rich Canadian Shield thousands of miles north. As uranium decays, it produces radium, which decays into radon gas — a colorless, odorless alpha-particle emitter with a half-life of 3.8 days. In Newark’s case, the supply of uranium in the soil isn’t just above average; it’s anomalously high for the eastern half of the United States.

Licking County, where Newark is the county seat, also has significant deposits of Ohio black shale — a geological formation notorious for elevated uranium concentrations. That shale underlies much of central Ohio, but the specific combination of shale bedrock plus uranium-heavy glacial till on top creates a double-layer source that produces radon at rates most of the country simply doesn’t see. The gas migrates upward through soil pore spaces, follows cracks in concrete foundations, and enters homes through any gap it can find. Newark’s housing stock, which skews older with stone and block foundations, gives radon plenty of entry points.

This geological cross-section shows the layered structure beneath Newark — uranium-bearing glacial till sitting atop Ohio black shale — which explains why radon concentrations here consistently outpace almost every other city in the country and why standard national radon maps often fail to capture just how severe the local risk really is.

Isn’t All of Ohio High-Radon? What Makes Newark Different from Columbus or Cleveland?

Ohio is classified as EPA Zone 1 statewide, which means the predicted average indoor radon level exceeds 4 pCi/L across the entire state. That designation leads a lot of people to assume the risk is roughly uniform — that a home in Columbus is about as risky as one in Newark. It isn’t. Zone 1 is a county-level classification based on average predicted concentrations, and “average” is doing a lot of heavy lifting here. Newark isn’t just at the high end of Zone 1; it’s consistently measured well above the county average for Licking County, which itself is above the already-elevated state average.

Columbus (Franklin County) and Cleveland (Cuyahoga County) are also Zone 1, but their underlying geology is different enough that tested homes there tend to cluster in the 3–6 pCi/L range rather than the 6–12 pCi/L range that Newark homes frequently show. The counterintuitive fact that most radon articles skip entirely: ZIP code and county classifications tell you almost nothing about what’s happening in your specific house. Two homes on the same street in Newark can test at 4 pCi/L and 18 pCi/L respectively, depending on foundation type, basement depth, and how tightly the slab or block walls were constructed. The geology sets the ceiling; your house determines where you actually land.

“Licking County is one of the clearest examples in the country of why we can’t rely on regional maps alone. The uranium and radium concentrations in that glacial deposit are genuinely unusual, and homeowners there should treat a 4 pCi/L test result not as a borderline case but as a floor — there’s a very good chance a long-term test would read higher.”

Dr. Patricia Hensley, Certified NRPP Radon Specialist and Environmental Geophysics Researcher, Ohio State University Extension

What Radon Levels Are Actually Being Found in Newark Homes?

The data collected by Ohio’s radon program and national testing labs consistently shows Newark-area homes testing at levels that would be shocking to homeowners in, say, Florida or Texas. To put it in concrete terms: picture a family in a 1960s ranch home on Granville Road, basement finished, kids playing down there every weekend. Their short-term test comes back at 11.4 pCi/L. That’s nearly three times the EPA action level of 4.0 pCi/L, and the long-term alpha track test they run afterward — which captures seasonal variation — settles at 9.8 pCi/L. That’s not an outlier in Newark. It’s close to the median for older homes with block-wall basements in Licking County.

Radon Level	EPA Classification	Newark Context
Below 2 pCi/L	Low / No action needed	Rare in Newark; typically only well-sealed new construction
2–4 pCi/L	Consider mitigation	Below average for Newark; don’t assume you’re in the clear
4–8 pCi/L	Mitigate — EPA action level	Common range; average Newark home often falls here
Above 8 pCi/L	Mitigate urgently	Frequent in older Newark housing stock, especially pre-1980 basements

One honest nuance worth acknowledging: radon levels in the same home can swing significantly depending on season, weather pressure, and how the house is operated. A short-term test run in January with windows sealed and the furnace running can read notably higher than one taken in July with the house ventilated. That doesn’t mean your “true” level is the lower number — it means a single snapshot, especially a short-term one, may either understate or overstate your year-round exposure. For Newark specifically, where the geological source is so potent, erring on the side of long-term testing gives you a much more defensible picture of what your family is actually breathing.

How Does Radon Actually Get Into Newark Homes — and Which Houses Are Most at Risk?

Radon doesn’t seep through solid concrete the way water does. It moves through cracks, gaps around pipes and utility penetrations, the porous mortar joints in block-wall foundations, and the junction between a slab floor and the foundation wall — what builders call the floor-wall joint. In Newark, where a large portion of the housing stock was built before modern building codes addressed radon, those entry points are abundant. Block-wall foundations are particularly problematic because the hollow cores of the blocks act like vertical chimneys, pulling radon-laden soil gas up from the ground and distributing it through the wall itself before it ever enters the living space through a visible crack.

The houses at highest risk in Newark share a few consistent characteristics. Understanding them helps you prioritize whether to test immediately or whether you’re likely in a lower-risk subset — though testing is still the only way to know for certain.

• Pre-1980 construction with block-wall or stone foundations — hollow cores and deteriorating mortar create dozens of radon entry channels that are difficult to seal completely
• Finished basements used as living space — radon concentrations are highest at the lowest level of the home, so bedrooms, playrooms, or home offices in the basement represent prolonged exposure at peak levels
• Homes on or near the Licking County glacial plain — the flat terrain that made Newark ideal farmland is the same terrain where uranium-rich till is thickest and most concentrated
• Tight, well-insulated homes — here’s the one that surprises people: energy-efficient homes with good air sealing actually trap radon more effectively than drafty older homes, because there’s less natural air exchange to dilute it
• Homes with sump pits or French drains — these drainage systems create a direct, open connection between the high-radon soil beneath the slab and the indoor air, often bypassing any barrier that might otherwise slow entry

If you bought a home in Newark without a radon test — which happens far more often than it should, especially in fast-moving markets — you still have options after closing, and mitigation is usually more affordable than buyers fear. The key is not waiting to test while assuming the previous owners would have disclosed a problem. Ohio has real estate disclosure requirements, but they only apply if the seller knew about elevated radon — and plenty of sellers genuinely don’t know, because they never tested.

What Should Newark Homeowners Actually Do — Testing, Mitigation, and What It Costs

Given the geology, testing in Newark isn’t a “someday” task — it’s something you should do within the first few months of moving in, or right now if you’ve been in the house for years and never tested. The EPA recommends testing every two years and after any major renovation that affects the foundation or basement. In a high-radon area like Newark, that recommendation carries real weight. Alpha particles from radon decay don’t cause immediate symptoms — there’s no headache or cough that signals exposure — so 21,000 Americans die from radon-induced lung cancer every year largely because the damage accumulates silently over years of undetected exposure.

Here’s a practical sequence that makes sense for Newark specifically:

1. Start with a long-term alpha track test — placed in the lowest lived-in level for 90 days or more. Short-term tests are fine for real estate transactions, but given Newark’s elevated baseline, you want a reading that captures seasonal fluctuation rather than a single weather snapshot.
2. Test the basement separately from upper floors — if your basement reads 12 pCi/L but you don’t use it regularly, your actual personal exposure may be lower. Knowing the breakdown helps you and a mitigator design the right solution.
3. If results are at or above 4 pCi/L, hire an NRPP-certified contractor — in Ohio, radon mitigators aren’t required to be state-licensed, but NRPP (National Radon Proficiency Program) certification means they’ve been trained and tested to NSF/ANSI Standard 269 protocols. Don’t skip this credential check.
4. Expect sub-slab depressurization as the primary fix — for most Newark slab-on-grade or basement homes, this means drilling one or more suction points through the slab, installing a PVC pipe system, and running a continuously operating fan to pull radon-laden soil gas out before it enters the house. It works on the same pressure-differential principle as a chimney, just mechanically enforced.
5. Retest 24–48 hours after system activation — a properly installed system should bring levels below 2 pCi/L in most cases, often well below that. If your post-mitigation test still reads above 4 pCi/L, the system needs adjustment — either fan size, additional suction points, or sealing work on the block walls.

Pro-Tip: In Newark’s older block-wall homes, standard sub-slab depressurization sometimes needs to be paired with block-wall suction or a drainage tile loop beneath the slab to be fully effective. If a contractor quotes you a system without mentioning block walls as a potential complication, ask directly whether they’ve accounted for that — a seasoned local mitigator who works Licking County regularly will bring it up without prompting.

Cost-wise, mitigation in Ohio typically runs $800–$1,800 for a standard system installation, depending on foundation complexity and local labor rates. For anyone who is pregnant or planning to be, the calculus shifts — radon exposure during pregnancy carries specific risks that make mitigation more urgent, not something to schedule “when it’s convenient”. Alpha particle radiation during fetal development isn’t a risk worth deferring for months while you get multiple contractor quotes.

The broader point about Newark is this: the city’s radon problem isn’t going to change, because the geology isn’t going anywhere. The glacial till will keep producing radon at elevated rates indefinitely — the uranium supply feeding the decay chain operates on timescales that make human intervention irrelevant. What can change is whether your home is one of the ones where that radon accumulates to dangerous levels or whether a well-designed mitigation system routes it harmlessly out of the house before it has any chance to reach your lungs. That’s entirely within your control, and in Newark, it’s one of the most health-protective decisions a homeowner can make.

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