Is Orange County, CA a radon risk area?

Orange County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Orange County sits at the 33rd percentile nationally for radon potential — above 33 of every 100 rated counties.

How Orange County compares

About 3,170,435 people live in Orange County, California, spread over 793.249 square miles. Population density there runs about 3,997 people per square mile. Rank 3 by population within its EPA zone puts Orange County at the 100th percentile among zone peers. Geologically, Orange County is grouped into EPA Region 9 alongside 94 other counties that share its rock and soil setting.

Zone vs. an actual test

At Zone 3, Orange 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. A Zone 3 label describes Orange County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Testing and mitigation in Orange County

Nothing about Orange 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 California's state radon program

Orange County's test kit answers today; a Airthings radon monitor keeps answering for Orange 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

Orange County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Orange County carries, the zone explainer covers what it does and doesn't tell you about any one house.