What EPA's radon map says about Horry County

EPA places Horry 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 31st percentile for radon potential — Horry County outranks 31% of every county EPA has rated.

Horry County by the numbers

About 413,391 people live in Horry County, South Carolina, spread over 1,133.151 square miles. Averaged across its land area, Horry County runs about 365 people per square mile. Among counties sharing Horry County's EPA zone, it outranks 94% of them by population. EPA's geology-based Region 4 groups Horry County with 735 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

At Zone 3, Horry County's predicted county average is under the national indoor average (~1.3 pCi/L) and well below EPA's 4 pCi/L action level — outdoor air nationally runs about 0.4 pCi/L for comparison. Don't read Zone 3 as a pass for Horry County — EPA's guidance to test every home makes no exception for counties predicted low.

If Horry County tests above the action level

Mitigation cost doesn't depend on Horry County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find South Carolina's state radon program

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

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Horry County carries, the zone explainer covers what it does and doesn't tell you about any one house.