Richland County, SC: EPA's radon zone, explained

EPA places Richland 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, Richland County ranks higher in radon potential than 31% of rated counties (the 31st percentile).

Where Richland County sits nationally

Richland County, South Carolina is home to about 430,651 people across 757.309 square miles. Averaged across its land area, Richland County runs about 569 people per square mile. By population, Richland County is the 62nd largest of every county sharing its EPA zone — the 94th percentile by population within that zone. Geologically, Richland County is grouped into EPA Region 4 alongside 735 other counties that share its rock and soil setting.

Zone vs. an actual test

At Zone 3, Richland 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 Richland County — EPA's guidance to test every home makes no exception for counties predicted low.

If Richland County tests above the action level

For a Richland County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find South Carolina's state radon program

For Richland County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Richland County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

Where Richland County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Richland County's numbers. Whatever zone Richland County carries, the zone explainer covers what it does and doesn't tell you about any one house.