Tap & Air

EPA radon zones

California radon map: every county's zone

2 of California's 58 counties are EPA radon zone 1 (predicted average above 4 pCi/L), 29 are zone 2 and 27 are zone 3. High readings occur in every zone, so EPA recommends testing every home.
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

How much does radon mitigation cost?

Most single-family systems cost $800 to $2,500 installed, depending on foundation type and how many suction points are needed. A follow-up test confirms the system works.

What do the zones mean?

EPA radon zones describe counties, not houses. Zone 1 counties have a predicted average indoor level above 4 picocuries per liter (pCi/L), Zone 2 between 2 and 4, Zone 3 below 2. Homes with high levels are found in every zone, which is why EPA recommends that every home be tested, and fixed at 4 pCi/L or above.

California cities: water and radon

Source: EPA Map of Radon Zones.