Radon by ZIP

Radon zones in California

Last updated

EPA’s Map of Radon Zones places 58 California counties in its three radon potential zones: 2 in Zone 1 (highest), 29 in Zone 2 (moderate), and 27 in Zone 3 (low).

2Zone 1 · Highest potential
29Zone 2 · Moderate potential
27Zone 3 · Low potential

What this means for California homes

Most California counties fall in Zone 2. EPA predicts moderate average indoor levels (2 to 4 pCi/L) across much of California. Many homes will be below the action level, but many will not, and only a test can tell which.

EPA’s guidance is the same everywhere: test your home, fix it if the level is 4 pCi/L or higher, and consider fixing between 2 and 4 pCi/L. The zone map is from 1993 and should not be used to decide whether a single home needs testing.

California radon program

EPA lists the following state contact for California: CA Indoor Radon Program, phone 916-449-5674. Website: www.cdph.ca.gov/radon. State programs can tell you about local testing data, free or discounted test kits, disclosure rules for home sales, and credentialed radon professionals.

California counties and their EPA radon zones

CountyEPA radon zone
Alameda CountyZone 2
Alpine CountyZone 2
Amador CountyZone 2
Butte CountyZone 3
Calaveras CountyZone 2
Colusa CountyZone 3
Contra Costa CountyZone 2
Del Norte CountyZone 3
El Dorado CountyZone 2
Fresno CountyZone 2
Glenn CountyZone 3
Humboldt CountyZone 3
Imperial CountyZone 3
Inyo CountyZone 2
Kern CountyZone 2
Kings CountyZone 3
Lake CountyZone 3
Lassen CountyZone 3
Los Angeles CountyZone 2
Madera CountyZone 2
Marin CountyZone 3
Mariposa CountyZone 2
Mendocino CountyZone 3
Merced CountyZone 3
Modoc CountyZone 3
Mono CountyZone 2
Monterey CountyZone 2
Napa CountyZone 3
Nevada CountyZone 2
Orange CountyZone 3
Placer CountyZone 2
Plumas CountyZone 2
Riverside CountyZone 2
Sacramento CountyZone 3
San Benito CountyZone 2
San Bernardino CountyZone 2
San Diego CountyZone 3
San Francisco CountyZone 2
San Joaquin CountyZone 3
San Luis Obispo CountyZone 2
San Mateo CountyZone 2
Santa Barbara CountyZone 1
Santa Clara CountyZone 2
Santa Cruz CountyZone 2
Shasta CountyZone 3
Sierra CountyZone 2
Siskiyou CountyZone 3
Solano CountyZone 3
Sonoma CountyZone 3
Stanislaus CountyZone 3
Sutter CountyZone 3
Tehama CountyZone 3
Trinity CountyZone 3
Tulare CountyZone 2
Tuolumne CountyZone 2
Ventura CountyZone 1
Yolo CountyZone 3
Yuba CountyZone 2

County names follow the 2020 Census. Zones from the EPA Map of Radon Zones (text version). Rows marked “zone of” use the zone EPA gave the predecessor or surrounding county.

Next steps: read how to test your home, check a result with the level calculator, or look up a single address by ZIP code.

Sources

  1. U.S. EPA, EPA Map of Radon Zones (text version)
  2. U.S. EPA, EPA Map of Radon Zones and Supplemental Information (state radon contacts)
  3. U.S. EPA, EPA Maps of Radon Zones and Supporting Documents by State