If you live in Greenville, Spartanburg, Anderson, Pickens or Oconee County, you have probably heard that radon "is a thing here." It is. But the useful question is not whether the Upstate has radon. It is what the numbers actually say and what they mean for your house.
This guide pulls together the public data in one place: South Carolina's own county test results, the EPA's radon zone map and the American Lung Association's estimates. Then we cover the part people tend to skip: what an average can and cannot tell you.
The short version
- The EPA recommends fixing a home at or above 4 pCi/L (picocuries per liter) and says to consider fixing between 2 and 4 pCi/L.
- For comparison, the EPA puts the average US home at about 1.3 pCi/L and outdoor air at about 0.4 pCi/L.
- Every one of the five Upstate counties has an average test result above the national home average, and each has recorded individual homes far above the action level.
- Greenville County is the only county in South Carolina in EPA Radon Zone 1. The other four Upstate counties are Zone 2.
- None of that predicts your house. Only a test does.
County-by-county radon test results
South Carolina's radon program publishes average results by county for initial tests. The figures below run through June 30, 2022, and come from the state's county summary (published by what is now the SC Department of Environmental Services, or SCDES).
| County | EPA zone | Initial tests | Average (pCi/L) | Highest (pCi/L) |
|---|---|---|---|---|
| Greenville | Zone 1 | 5,220 | 3.4 | 126.6 |
| Spartanburg | Zone 2 | 1,136 | 2.6 | 41.0 |
| Anderson | Zone 2 | 711 | 1.7 | 38.0 |
| Pickens | Zone 2 | 726 | 3.0 | 48.1 |
| Oconee | Zone 2 | 1,045 | 5.0 | 37.1 |
A few things jump out:
- Oconee County has the highest average of the five at 5.0 pCi/L, which is above the EPA action level on its own, even though Oconee is a Zone 2 county.
- Greenville County has by far the most tests and an average of 3.4 pCi/L, squarely in the EPA's "consider fixing" range. Its highest recorded result, 126.6 pCi/L, is more than 30 times the action level.
- Pickens (3.0) and Spartanburg (2.6) also average inside the 2 to 4 range.
- Anderson County averages 1.7, the lowest of the group, but it still has a recorded high of 38.0 pCi/L.
If you are in Seneca or elsewhere in Oconee County, or in Easley, Clemson or the rest of Pickens County, the averages are a good reason not to put testing off. You can read more on our Seneca and Easley pages.
What the EPA radon zones mean here
The EPA's radon zone map sorts counties by their potential for elevated indoor radon. Zone 1 is the highest potential and Zone 3 the lowest. The map dates to 1993 and was updated in 2019.
Statewide, South Carolina has 1 Zone 1 county, 8 Zone 2 counties and 37 Zone 3 counties. The one Zone 1 county is Greenville. Spartanburg, Anderson, Pickens and Oconee are all Zone 2. In other words, the Upstate holds the state's only highest-potential county and several of its moderate-potential ones.
The EPA is clear that the zone map is a planning tool, not a verdict on any home. Its guidance is to test every home regardless of zone. The Oconee numbers above show why: a Zone 2 county can still post the highest average in the region. For more on the Zone 1 designation, see our post on why Greenville County is SC's only Zone 1 county.
A second data set: American Lung Association estimates
The American Lung Association looked at South Carolina radon data from 2008 through 2017. Its findings line up with the state numbers:
- Greenville County had the most radon tests in the state over that period, 12,004, with an estimated mean of 2.9 pCi/L.
- Oconee County had the highest estimated average in the state, about 4.8 pCi/L.
- The estimated statewide mean was 1.7 pCi/L.
Different years and methods, same pattern: the Upstate, and Oconee and Greenville counties in particular, run higher than the rest of South Carolina.
What county averages don't tell you
Averages are useful for one thing: telling you whether radon is common enough in your area to take seriously. In the Upstate, it clearly is. Beyond that, they have real limits.
Neighbors can test very differently
Radon comes from the soil and rock under a home. How much gets inside depends on the ground under that specific lot and on how the house is built and sealed. Two houses on the same street can test far apart. A county average of 1.7 does not mean your Anderson home is at 1.7, and an average of 5.0 does not mean your Oconee home is high.
The averages come from homes that were tested
These are results from homes whose owners chose to test, not a survey of every house in the county. Counties with fewer tests, like Anderson and Pickens with a little over 700 each, have less data behind their averages.
An average hides the high end
Look at the "highest" column again. Every Upstate county has recorded homes at roughly 9 to 30 or more times the action level. Those homes are part of the average too, and you cannot tell from the average whether yours is one of them.
Foundation type matters
Many Upstate homes sit on crawl spaces or slabs, and older homes may have basements. Each lets soil gas in differently, and each is fixed differently. Our guide to radon in crawl space homes covers the most common setup we see.
Already have a number? If your test came back at 4 pCi/L or higher, or between 2 and 4 and you want it lower, we can look at your foundation and give you a clear written estimate. Get a free quote.
How to get your own number
Testing is simple and inexpensive compared with almost anything else you do to a house.
- Test the lowest lived-in level. That is a finished basement if you use it, otherwise the main floor. Not the crawl space itself.
- Pick a test length. Short-term tests run 2 to 90 days. Long-term tests run more than 90 days and give a better picture of your year-round average.
- Keep the house closed. For short-term tests, keep windows and exterior doors closed for 12 hours before and during the test, apart from normal coming and going.
- Act on the result. At 4 pCi/L or above, the EPA recommends fixing the home. Between 2 and 4, consider it. Our post on radon between 2 and 4 pCi/L walks through that decision.
South Carolina offers one free test kit per home while supplies last through SCDES. You can also buy a kit or hire a professional; our comparison of DIY and professional radon tests explains when each makes sense, and our radon testing page covers how we do it.
What it costs to bring levels down
If your result is high, the fix is usually an active soil depressurization system: a sealed pipe and a quiet in-line fan that pull radon from under the house and vent it above the roof. Typical ranges in our area:
- Sub-slab depressurization (slab or basement): typical range $900–$2,500
- Crawl space sub-membrane system: typical range $1,500–$3,500
- Combination foundations: typical range $2,200–$3,800
These are estimates; your final price comes after an on-site look. See our full radon mitigation cost guide for details, or start with our main radon mitigation page. Whatever system goes in, retest afterward to confirm the level dropped.
Frequently asked questions
Which Upstate SC county has the highest radon levels?
Based on South Carolina's initial test results through June 2022, Oconee County has the highest average of the five Upstate counties at 5.0 pCi/L, above the EPA action level of 4. Greenville County averages 3.4 and has the highest single recorded result, 126.6 pCi/L. The American Lung Association's 2008–2017 review also found Oconee had the highest estimated average in the state.
Does a low county average mean I don't need to test?
No. Radon levels vary from house to house depending on the soil under the lot and how the home is built. Anderson County averages 1.7 pCi/L but has recorded a home at 38.0. The EPA recommends testing every home regardless of zone or county average. A test is the only way to know your own level.