Radon in the Upstate: why Greenville tests high

Greenville County sits in the only Zone 1 ring the Environmental Protection Agency draws anywhere in the Upstate, the agency's highest radon-potential category, while every county around it sits one band down. South Carolina's own homeowner testing backs that up: through June 2022, Greenville had more radon tests on file than any other county in the state, and the average came in just under the point where EPA says to fix a house. The zone and the average both describe the county. Only a test describes your house.

Why does Greenville County test high for radon?

EPA's Map of Radon Zones, first drawn in 1993 from geology, soil radioactivity and foundation data, puts Greenville County alone among the Upstate's counties in Zone 1, the category for counties with a predicted average indoor radon screening level above 4 picocuries per liter (pCi/L). Pickens, Oconee, Anderson, Laurens, Spartanburg, Cherokee and York sit one band down, in Zone 2, predicted between 2 and 4 pCi/L. The rest of South Carolina falls into Zone 3, under 2 pCi/L. EPA is blunt about what the map cannot tell you: "The map should not be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested for radon."

South Carolina's own numbers back the county up, and go further. The state's radon program has logged homeowner test results by county since free kits went out, and through June 30, 2022, Greenville had 5,220 homes tested, by far the most of any South Carolina county and more than four times the next-highest, Lexington's 1,329. The average Greenville result was 3.4 pCi/L, just under the 4.0 pCi/L point where EPA recommends fixing a home. The highest single Greenville test on that list came back at 126.6 pCi/L, more than thirty times the action level.

What radon level means you should fix your home?

EPA sets the same threshold nationwide. Fix a home once a confirmed radon level is 4 pCi/L or higher; radon levels less than 4 pCi/L still pose a risk, and in many cases can be reduced further. The agency recommends homeowners "consider fixing" anywhere from 2 to 4 pCi/L. The stakes are the reason for the threshold at all: radon is the leading cause of lung cancer among people who have never smoked and the second-leading cause of lung cancer overall, after smoking, and EPA attributes roughly 21,000 lung cancer deaths a year to it nationwide, about 2,900 of them in people who never smoked.

Why do radon tests usually happen as winter sets in?

Radon can build up indoors at any time of year, but EPA's own regional office has made the seasonal case plainly: "it's during the cold winter months when our houses are shut tight to retain heat that radon is most likely to accumulate," and "the best time to test your home for radon is during the winter months when windows are closed." A closed house lets in less outdoor air to dilute whatever radon is seeping up through the foundation, so a test run while the Upstate's homes are sealed against the cold reads closer to a worst case than one run with the windows open in April.

How do you test a house for radon in South Carolina?

There are two kinds of kit. A short-term test stays in the home for two to 90 days, run for a minimum of 48 hours, and gives a faster but rougher reading; a long-term test runs more than 90 days and gives a better picture of a home's year-round average. Passive devices, the kind that do not need power, are generally inexpensive; active devices need power and usually cost more. South Carolina's radon program, run today by the state Department of Environmental Services, offers a free short-term kit to South Carolina homeowners while supplies last, requested at des.sc.gov/radon, and a free follow-up kit if that first result comes back at or above 4.0 pCi/L. The program does not supply kits for real estate transactions; EPA publishes a separate pamphlet, the Home Buyer's and Seller's Guide to Radon, for testing tied to a sale.

What does a radon mitigation system actually do?

EPA generally recommends soil suction, and the method works before radon gets inside rather than after. A contractor runs one or more sealed pipes from beneath the slab or the crawlspace membrane up through the house and out above the roofline, where a fan continuously draws radon out from under the foundation and vents it into outdoor air before it ever reaches a living space. A contractor may run diagnostic tests first, tracing chemical smoke through cracks, drains and sumps, or pulling a vacuum hose against the foundation to see how easily air moves underneath it, to decide which system design will actually work for that house. Done well, EPA says these systems "can reduce radon levels in your home by up to 99 percent," and that "most homes can be fixed for about the same cost as other common home repairs," though the real number depends on a home's size, foundation type and which method the diagnostics point to. A fan-driven system also adds a little to the electric bill, which is worth asking a contractor to estimate before signing anything. EPA recommends hiring a state-certified or otherwise qualified mitigation contractor, getting more than one written estimate, and putting the total cost, the timeline and any guarantee to reach an agreed radon level in a signed contract before work starts.

Does being in Zone 1 mean every Greenville house tests high?

No. EPA's own map carries that caveat for a reason South Carolina's testing data illustrates directly. Oconee County, one tier down in Zone 2, posted the highest average radon result of any South Carolina county in the state's 2022 testing data, 5.0 pCi/L, above the level where EPA says to fix a house. Greenville, the only Upstate county EPA rates Zone 1, averaged 3.4 pCi/L, below it. A county-wide zone or average is a starting point for understanding risk across a region, not a verdict on one address. A Greenville home can test low, and a home one county over, rated "moderate," can test well above the action level. The only way to know what a specific house is holding is to test it.

Where this fits for a buyer or seller

A radon test is not something a real estate agent runs, and the team is not a lab or a mitigation contractor. Advantage Inspection Upstate, the inspection firm on the team's vendor list, adds radon testing as an option alongside a home or new-construction inspection, which is the practical way most Greenville buyers end up testing a house before they are living in it. A seller who wants certainty ahead of listing, or an owner whose house has sat closed up all winter, can request a free short-term kit from South Carolina's own radon program instead and get a baseline before the heating season ends.