Is Williamsburg County, SC a radon risk area?

EPA places Williamsburg County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally that's the 18th percentile for radon potential — Williamsburg County outranks 18% of every county EPA has rated.

How Williamsburg County compares

About 29,865 people live in Williamsburg County, South Carolina, spread over 934.166 square miles. That works out to roughly 32 people per square mile. Rank 482 by population within its EPA zone puts Williamsburg County at the 53rd percentile among zone peers. Geologically, Williamsburg County is grouped into EPA Region 4 alongside 735 other counties that share its rock and soil setting.

What this actually means for a house in Williamsburg County

Williamsburg County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. A Zone 3 label describes Williamsburg County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

If Williamsburg County tests above the action level

Nothing about Williamsburg County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find South Carolina's state radon program

Williamsburg County's test kit answers today; a Airthings radon monitor keeps answering for Williamsburg County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

More on how this number was built

Williamsburg County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.