Is San Joaquin County, CA a radon risk area?

EPA places San Joaquin 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. San Joaquin County sits at the 32nd percentile nationally for radon potential — above 32 of every 100 rated counties.

Where San Joaquin County sits nationally

About 816,108 people live in San Joaquin County, California, spread over 1,392.301 square miles. Averaged across its land area, San Joaquin County runs about 586 people per square mile. Rank 38 by population within its EPA zone puts San Joaquin County at the 96th percentile among zone peers. Geologically, San Joaquin County is grouped into EPA Region 9 alongside 94 other counties that share its rock and soil setting.

What this actually means for a house in San Joaquin County

A Zone 3 county like San Joaquin County is predicted closer to the 0.4 pCi/L typical outdoors than to EPA's 4 pCi/L action level. Don't read Zone 3 as a pass for San Joaquin County — EPA's guidance to test every home makes no exception for counties predicted low.

If San Joaquin County tests above the action level

Nothing about San Joaquin 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

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

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed San Joaquin County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.