Radon Levels in South Carolina
By Daniel SmokeDirector of Operations
Radon is present across South Carolina, but how much accumulates in any given home varies widely, by region, by geology, and by how the house is built. Some areas of the state, particularly the Upstate, tend to produce higher radon readings than others. But local averages only tell you the odds; the only way to know your home's actual level is to test it.
Radon Risk Varies Across the State
South Carolina spans several geologic regions, and radon potential changes with them. The Upstate and Piedmont, the rolling, granite-rich interior, carries the state's highest radon potential, while the sandy coastal plain runs low.
On the EPA Map of Radon Zones, Greenville County is the only county in South Carolina rated Zone 1 (the highest); the surrounding Upstate counties are Zone 2, and the Midlands, Pee Dee, and coast are Zone 3 (lowest).
County test averages compiled by the SC Department of Environmental Services (SC DES) show the same gradient: several Upstate counties average at or near the 4.0 pCi/L action level, while coastal counties average well under 1.0. Even so, elevated radon has turned up in homes in every part of the state.
| County | EPA zone | SC DES average |
|---|---|---|
| Oconee | Zone 2 | 5.0 pCi/L |
| Greenville | Zone 1 (highest) | 3.4 pCi/L |
| Pickens | Zone 2 | 3.0 pCi/L |
| Spartanburg | Zone 2 | 2.6 pCi/L |
| Charleston (coast) | Zone 3 | 0.9 pCi/L |
| Horry / Myrtle Beach (coast) | Zone 3 | 0.8 pCi/L |
Why the Upstate Tends to Run Higher
Radon comes from the natural breakdown of uranium in soil and rock. The Piedmont geology underlying the Upstate contains more of the granitic rock associated with radon production, so soil gas in these areas can carry more radon into homes through foundation cracks and openings. The counties most often flagged as higher-risk are concentrated in this region:
- Greenville County, the only EPA Zone 1 county in the state, averaging about 3.4 pCi/L across more than 5,000 SC DES test results.
- Oconee County, the highest Upstate average on record at roughly 5.0 pCi/L (EPA Zone 2).
- Pickens, Spartanburg, Cherokee, and Anderson, other Upstate Zone 2 counties along and below the Blue Ridge.
- Homes with basements or crawlspaces anywhere in the Upstate, which give soil gas more entry points.
Local Averages Do Not Predict Your Home
Two houses on the same street can have very different radon levels depending on their foundation, construction, and how they are operated. A regional map tells you the general likelihood, not your result. The EPA recommends that every home be tested regardless of its area's zone, because a 'low-risk' map designation does not mean an individual home is safe. It only means elevated levels are statistically less common.
What an Elevated Result Means
The EPA action level is 4 pCi/L. At or above that level, mitigation is recommended to reduce your exposure. Radon is the second leading cause of lung cancer in the United States, and because it is invisible and odorless, testing is the only way to detect it. If your result is elevated, a mitigation system can typically bring levels well below the action level.
How Much Does Radon Mitigation Cost in South Carolina?
Mitigation costs in South Carolina fall within the same national range. Most residential systems run about $800 to $2,500 installed, with many homeowners paying around $1,200 to $1,500. The exact price depends on your foundation type and how complex the system needs to be, not on the state. Upstate homes with basements or crawlspaces can sit anywhere in that range depending on the design. Our radon mitigation cost guide breaks down what drives the price and the small monthly cost to run the fan.
Testing in South Carolina
Whether you are in the Upstate, the Midlands, or along the coast, testing is straightforward and is the right first step. Peerless Environmental supports radon testing for properties across the Southeast, including communities throughout South Carolina, and can walk you through mitigation options if a result comes back high.
Sources
The radon figures on this page come from these primary sources:
- U.S. EPA: Map of Radon Zones (county radon zone designations).
- SC Department of Environmental Services: Average In-Home Radon Concentrations by County (SC Radon Program test results for un-mitigated homes through 6/30/2022).
Common Questions
Which South Carolina counties have the highest radon levels?
The Upstate counties run highest. On the SC DES county averages, Oconee leads at about 5.0 pCi/L and Greenville averages 3.4 pCi/L across more than 5,000 tests; Greenville is also the only county the EPA rates Zone 1. Neighboring Upstate counties like Pickens, Spartanburg, and Cherokee are EPA Zone 2. Coastal counties such as Charleston and Horry average under 1.0 pCi/L, but elevated radon still turns up in homes statewide.
Is radon a problem in Greenville, SC?
Yes. Greenville is the only South Carolina county the EPA rates Zone 1 (its highest), and SC DES testing puts the county average around 3.4 pCi/L. That is below the 4.0 pCi/L action level on average, but averages hide wide variation, and many individual Greenville homes test well above it. Testing is the only way to know a specific home's level.
Do I need to test for radon if I don't live in the Upstate?
Yes. A lower regional average only means elevated levels are statistically less common, not that any given home is safe. The EPA recommends testing every home regardless of its area's radon zone, because foundation type and construction can produce a high reading even in a lower-risk area.
How often should I retest for radon in South Carolina?
The EPA recommends retesting about every two years for most homes, and sooner after any major foundation or HVAC change. If you have a mitigation system, confirm it is still working with a periodic retest.
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