Trinity County, CA: EPA's radon zone, explained

Trinity 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 Trinity County in the 11th percentile nationally for radon potential — higher than 11% of the counties EPA has rated.

How Trinity County compares

Trinity County, California is home to about 15,642 people across 3,179.268 square miles. Averaged across its land area, Trinity County runs about 5 people per square mile. By population, Trinity County is the 700th largest of every county sharing its EPA zone — the 32nd percentile by population within that zone. EPA's geology-based Region 9 groups Trinity County with 94 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Trinity County

A Zone 3 county like Trinity County is predicted closer to the 0.4 pCi/L typical outdoors than to EPA's 4 pCi/L action level. A Zone 3 label describes Trinity 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 Trinity County

For a Trinity County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find California's state radon program

For Trinity County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Trinity 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 Trinity County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Trinity County's numbers. Whatever zone Trinity County carries, the zone explainer covers what it does and doesn't tell you about any one house.