Humboldt County, CA radon potential

Humboldt County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. That puts Humboldt County in the 27th percentile nationally for radon potential — higher than 27% of the counties EPA has rated.

Where Humboldt County sits nationally

Humboldt County, California is home to about 132,380 people across 3,568.025 square miles. Population density there runs about 37 people per square mile. Within its own EPA zone, Humboldt County is bigger by population than 82% of the counties that share it. Humboldt County falls in EPA Radon Region 9, one of 95 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

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

Testing and mitigation in Humboldt 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 Humboldt County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Humboldt County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where Humboldt 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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.