Yes. Every Central Ohio county sits in EPA Radon Zone 1, and Franklin County's 16,142 pre-mitigation tests from 2008 to 2017 had an estimated mean of 9.5 pCi/L, more than twice the EPA action level of 4.0.
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The county figure comes from an American Lung Association analysis of CDC tracking data, and it agrees with much older state work: the 1988-89 EPA and Ohio residential survey found 64 percent of 170 Franklin County homes above 4 pCi/L on short screening tests. The cause is geology. The Ohio Shale, the largest uranium source in the state, runs in a north-south band under Franklin and Delaware counties, and glaciers smeared shale and limestone debris across the region. The health stakes come from the EPA: about 21,000 US lung cancer deaths a year are tied to radon, roughly 2,900 of them among people who never smoked. None of that predicts a single house. Averages describe the region, and only a test tells you what your own basement is doing. See why Ohio radon runs high.