Is Solano County, CA a radon risk area?

Solano County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Nationally, Solano County ranks higher in radon potential than 31% of rated counties (the 31st percentile).

Where Solano County sits nationally

About 455,101 people live in Solano County, California, spread over 821.738 square miles. Averaged across its land area, Solano County runs about 554 people per square mile. Rank 56 by population within its EPA zone puts Solano County at the 95th percentile among zone peers. EPA's geology-based Region 9 groups Solano County with 94 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

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

Next steps for a home in Solano County

Nothing about Solano 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

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

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Solano County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.