If you live in Cleveland, Akron, Youngstown, Canton, or anywhere in Northeast Ohio, the rock beneath your house is the single biggest factor in your home's radon profile. The Devonian Ohio Shale — a black, organic-rich, uranium-bearing shale formed approximately 360 million years ago — underlies most of the region and is one of the most radon-productive bedrock units in the eastern United States.
What is the Ohio Shale?
The Ohio Shale is a Devonian-age (Late Devonian, ~360 Ma) marine black shale that formed at the bottom of a shallow inland sea that covered much of what is now Ohio. The shale contains 1-20% organic carbon (one of the highest concentrations of any U.S. shale formation), along with trace uranium incorporated during deposition. Today, the Ohio Shale outcrops or sits at shallow depth across most of Northeast Ohio — including Cuyahoga County (Cleveland), Summit County (Akron), Mahoning County (Youngstown), and Stark County (Canton).
How does Ohio Shale produce radon?
Uranium in the shale decays through a multi-step chain that eventually produces radium-226, which in turn decays to radon-222 — the radioactive gas that enters homes through soil gas migration. Because the Ohio Shale sits directly beneath much of Northeast Ohio's surface, radon-rich soil gas has a short distance to travel before reaching the soil above home foundations. When that soil gas encounters cracks in basement floors, sump pits, pipe penetrations, or crawl-space openings, it enters the home and concentrates indoors.
The result: counties underlain by Ohio Shale consistently show some of the highest indoor radon averages in the state. Mahoning County (Youngstown) averages ~5.8 pCi/L; Summit County (Akron) averages ~5.5 pCi/L; Cuyahoga County (Cleveland) averages ~5.2 pCi/L — all well above the EPA action level of 4 pCi/L.
Which Ohio counties are underlain by Ohio Shale?
The Ohio Shale belt runs in a roughly north-south arc across Northeast and Central Ohio:
- Northeast Ohio: Cuyahoga, Summit, Mahoning, Stark, Portage, Trumbull, Geauga counties
- North-Central Ohio: Richland, Ashland, Wayne, Holmes counties
- Central Ohio: Franklin (Columbus), Licking, Delaware counties (deeper, with glacial till cover)
- South-Central Ohio: Ross, Pike, Scioto counties (shallow exposure)
What does this mean for radon mitigation?
When the bedrock beneath a home is Ohio Shale (or close to it), active sub-slab depressurization (ASD) remains the gold standard mitigation approach. However, NRPP- and ODH-licensed contractors in Northeast Ohio adapt the design in several ways:
- Higher-CFM fans: Shale-source radon often requires stronger suction (higher inlet flow) to maintain negative pressure relative to a uranium-rich bedrock source
- Deeper suction points: Drilling through the basement slab to within several inches of the shale-soil interface improves capture efficiency
- Sealed sump basins: Sump pits are particularly vulnerable in shale-bedrock areas because they often penetrate near or into the radon source rock
- Post-mitigation verification testing after 48-72 hours of system operation, with adjustments as needed to bring indoor levels below 2 pCi/L
What about Southwest and Southwest Ohio?
The radon story is different in Southwest Ohio (Cincinnati, Dayton). There the bedrock is dominated by Ordovician-age Cincinnati Arch limestone and shale (Kope, Fairview, Waynesville Formations) — also uranium-bearing, but with different geochemistry than Ohio Shale. Both regions are EPA Zone 1 (highest radon potential), but the mitigation approach varies by bedrock type.
Bottom line
If your home is in Northeast Ohio, plan for radon testing as a baseline expectation — not an unusual finding. The Ohio Shale beneath the region is a primary radon source. The good news: properly designed sub-slab depressurization systems consistently bring indoor levels from above 8 pCi/L down to under 2 pCi/L. Use a contractor who is both NRPP-certified and ODH-licensed per Ohio Admin. Code Chapter 3701-69, and request a post-mitigation verification test in writing.