Is Fairfax County, VA a radon risk area?

Fairfax County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally, Fairfax County ranks higher in radon potential than 100% of rated counties (the 100th percentile).

Fairfax County by the numbers

About 1,160,925 people live in Fairfax County, Virginia, spread over 391.021 square miles. Population density there runs about 2,969 people per square mile. Rank 5 by population within its EPA zone puts Fairfax County at the 100th percentile among zone peers. EPA's geology-based Region 3 groups Fairfax County with 244 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Fairfax County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Fairfax County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Fairfax County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Fairfax County

Nothing about Fairfax 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 Virginia's state radon program

Fairfax County's test kit answers today; a Airthings radon monitor keeps answering for Fairfax 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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.