Sonoma County, CA radon potential

EPA places Sonoma 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. Rank it against the rest of the country and Sonoma County lands in the 31st percentile for radon potential.

Sonoma County by the numbers

Sonoma County, California is home to about 485,375 people across 1,575.337 square miles. Averaged across its land area, Sonoma County runs about 308 people per square mile. Within its own EPA zone, Sonoma County is bigger by population than 95% of the counties that share it. EPA's geology-based Region 9 groups Sonoma County with 94 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Sonoma County

Sonoma County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. Low doesn't mean zero: EPA's own data shows homes in Zone 3 counties like Sonoma County testing above the action level often enough that skipping a test isn't the safe assumption.

Testing and mitigation in Sonoma County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find California's state radon program

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

Where Sonoma County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.