Is Butte County, CA a radon risk area?

EPA places Butte 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. Nationally that's the 29th percentile for radon potential — Butte County outranks 29% of every county EPA has rated.

Where Butte County sits nationally

About 208,334 people live in Butte County, California, spread over 1,636.511 square miles. Population density there runs about 127 people per square mile. Rank 126 by population within its EPA zone puts Butte County at the 88th percentile among zone peers. Geologically, Butte County is grouped into EPA Region 9 alongside 94 other counties that share its rock and soil setting.

Zone vs. an actual test

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

If Butte County tests above the action level

Nothing about Butte 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

Butte County's test kit answers today; a Airthings radon monitor keeps answering for Butte 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

Butte County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Butte County carries, the zone explainer covers what it does and doesn't tell you about any one house.