Radon in Delaware County, OH: Test Results and Mitigation Cost

Delaware County, just north of Columbus, has one of the highest radon test failure rates in Ohio's busiest testing region. The Ohio Department of Health county dashboard lists 23,086 pre-mitigation tests for the county, and 49.64% of them read at or above EPA's 4 pCi/L action level (ODH data, 2010 to present, retrieved Oct 16, 2026).

That compares with 34.4% for the state as a whole by our test-weighted count of the ODH file. ODH lists Delaware County's geometric mean at 3.89 pCi/L and its arithmetic mean at 5.95 pCi/L. EPA's 1993 map puts the county in Zone 1, and all 10 ZIP areas centered in the county in the Census Bureau file are Zone 1.

For a typical Delaware County basement home, HomeGuide's Feb 2026 survey prices a sub-slab system at $1,200 to $2,000 installed, with a national average of $1,600.

Licensing and permits

Ohio licenses radon work: under Ohio Administrative Code Chapter 3701-69 (for example OAC 3701-69-04), ODH licenses radon testers, mitigation specialists and mitigation contractors. Ask a bidder for both the specialist's license and the contractor's.

Verify before signing: ODH publishes a radon licensure data set on data.ohio.gov that lists current licensees.

Local permits: Delaware County's townships and cities set their own building and electrical permit rules; some want a permit for the fan circuit. HomeGuide reports radon permits at $25 to $150 where required.

New subdivisions: much of the county was built after 1990. Ask whether your builder left a passive radon pipe; adding a fan to one was about $300 in EPA's 2010 guide (2010 dollars).

Local conditions

The Ohio DNR Geological Survey ties high indoor radon in central Ohio to glacial till that carried fragments of uranium-bearing Ohio Shale, and to permeable sand and gravel that lets soil gas move. In Delaware County, the Ohio Shale crops out along the Olentangy River north of Columbus, and glacial till blankets the uplands east and west of it.

ODH data for the neighboring counties shows the same regional pattern: Franklin County (Columbus) logged 114,203 tests with 44.88% at or above 4 pCi/L, Morrow County to the north 721 tests at 51.60%, Licking County to the east 11,407 at 51.08%, and Union County to the west 4,094 at 43.11% (ODH data).

ODH's file lists a maximum single reading of 260.9 pCi/L in Delaware County. Extremes like that are rare, but they are why EPA tells every household to test rather than rely on a county figure.

What drives local prices

Newer basement homes along US 23 and around Powell and Lewis Center usually take one sub-slab point, $1,200 to $2,000 based on HomeGuide's published survey.
Large homes in the county's southern townships may need more suction; our calculator uses an est. ×1.25 at 2,500 sq ft or more, and HomeGuide's range runs $2,500 or more for large homes.
Slab additions and bonus rooms over a basement can mean a second suction area, an est. ×1.5.
Permit $25 to $150 where required, and a professional retest $125 to $400 (HomeGuide).
Ohio's licensing rule adds training and reporting costs for installers compared with unregulated states (Cornelia Cove estimate).

Common jobs

Sub-slab systems in newer basement homes in Liberty, Orange and Genoa townships.
Fan activation on builder-installed passive pipes.
Systems for older farmhouses and village homes in Sunbury, Galena and Ostrander.
Inspection-period tests and fixes in a fast-moving resale market.

From test to fixed, and where we cover

Step 1: test with an ODH-licensed tester or a kit in the lowest lived-in level. Step 2: at 4 pCi/L or more, get two bids from ODH-licensed mitigation contractors.

Step 3: compare each bid with the calculator. Step 4: retest after the system runs at least 24 hours (EPA Consumer's Guide).

We cover Delaware, Powell, Lewis Center, Sunbury, Galena, Ostrander, Ashley and the Delaware County part of Westerville, along I-71, US 23, US 36 and State Route 315.

Communities: Delaware, Powell, Lewis Center, Sunbury, Galena, Ostrander, Ashley, Westerville

Before you sign

A high result is a reason to act within weeks, not hours (EPA Citizen's Guide). Check the ODH license, get the fan warranty in writing, and schedule a post-mitigation test.

Questions about Delaware County

How common is high radon in Delaware County, Ohio?

49.64% of 23,086 tests in the ODH county dashboard read 4 pCi/L or higher.

Why is radon high north of Columbus?

The Ohio DNR Geological Survey links central Ohio radon to glacial till carrying Ohio Shale fragments and to permeable sand and gravel.

Does my Ohio mitigator need a license?

Yes. ODH licenses mitigation specialists and contractors under OAC Chapter 3701-69.

What does a radon system cost in Delaware County?

HomeGuide's national survey puts a sub-slab system at $1,200 to $2,000; get two ODH-licensed bids.

Sources

Nearby counties

Radon in Ohio (statewide)

Rules and fees change; confirm with the state radon office. Price your own system with the radon mitigation cost calculator, read the radon mitigation cost guide, or check any ZIP with the radon levels by ZIP tool.