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California Radon Map and Levels by County

California's counties span all three EPA radon zones. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    10.0%

    26.0 pts below U.S.

    California
    10.0%
    U.S.
    36.0%

    9,969 tests across 54 counties, 2005 to 2014

  • Rank among states

    45 of 47

    Ten lowest states

    California
    10.0%
    Nebraska
    60.4%

    By share, every state pooled the same way, 2005 to 2014

  • Counties in EPA Zone 1

    2 of 58

    Some at highest potential

    Zone 1
    2
    Zone 2
    29

    Most counties sit in Zone 2; Zone 1 is the highest potential

  • Highest county

    33.3%

    El Dorado County

    El Dorado
    33.3%
    Yolo
    0.0%

    Counties with 30+ tests, 2005 to 2014

Read a result for California

Starts at EPA's action level

4.0pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 4.0 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. 10.0% of California's reported tests reached 4 pCi/L, 2005 to 2014.

Interpret this readingWhat a fix costs

The data

California, At a glance

California at a glance

Predicted: EPA radon zone

58 of 58 counties classified

EPA classifies counties, not states. Of the 58 counties in California with a zone, 2 are in Zone 1, 29 in Zone 2 and 27 in Zone 3.

  • Zone 1: Highest predicted potentialgreater than 4 pCi/L2 of 58 counties · 3.4%
  • Zone 2: Moderate predicted potential2 to 4 pCi/L29 of 58 counties · 50.0%
  • Zone 3: Lower predicted potentialless than 2 pCi/L27 of 58 counties · 46.6%

An EPA radon zone predicts a whole county. It is not intended to determine whether any individual home should be tested: homes with elevated levels occur in all three zones, and EPA recommends testing every home regardless of zone.

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

CDC test figures, county by county

CDC publishes California's radon test figures by county: 56 of its 58 counties have one. Each one's share is in the county list.

How to read these figures

California, Compared

California radon figures, compared

Calculated by Radon411
California, 2005 to 2014, laboratory
10.0%
of 9,969 tests at or above 4 pCi/L, pooled
Against the U.S.
−26.0points
36.0% pooled
Rank among the states
45 of 47
1 is the highest share
Counties with 30 or more tests
34
Highest
33.3%
El Dorado County
Lowest
0.0%
Yolo County

Fewer reported tests reach 4 pCi/L in California than in most states: 10.0% of 9,969 over the 2005 to 2014 laboratory totals, from 54 counties. Nationally the pooled share is 36.0%: 26.0 points higher than here. Among 47 states pooled the same way it ranks 45th, with Texas (10.6%) above it and District of Columbia (8.0%) below.

El Dorado County reports the highest share (33.3% of 303 tests) and Yolo County the lowest (0.0%); the most tests came from Los Angeles County, 2,302 of them at 9.2%. EPA's 1993 map puts 2 of its 58 classified counties in Zone 1; the tests reported since bear that out at 10.0%.

By band, 1 county at 30% to 50%, 6 counties at 15% to 30%, 19 counties at 5% to 15%, 8 counties at under 5%. Across its 4 overlapping ten-year totals, the share went from 10.0% (2005 to 2014) to 10.3% (2008 to 2017), within 2 points, with 2006 to 2015 the highest at 10.6%.

California ranked among 47 states by pooled share of tests at or above 4 pCi/L, 2005 to 2014, laboratory
StateRankCountiesTestsAt or above 4 pCi/L
Alabama37 of 476113,77222.4%
Florida38 of 476233,54222.1%
Vermont39 of 47148,58821.6%
South Carolina40 of 474621,84319.8%
Delaware41 of 4738,69117.9%
Arizona42 of 47123,04417.4%
Oklahoma43 of 474981712.0%
Texas44 of 471403,72110.6%
California45 of 47549,96910.0%
District of Columbia46 of 4711,7358.0%
Louisiana47 of 47364222.6%
California's highest and lowest counties with 30 or more tests, by share at or above 4 pCi/L, 2005 to 2014, laboratory
CountyRankTestsAt or above 4 pCi/L
El Dorado County1 of 3430333.3%
Nevada County2 of 3423928.9%
Tulare County3 of 348127.2%
Tuolumne County4 of 346524.6%
Amador County5 of 343724.3%
San Joaquin County6 of 346520.0%
Santa Cruz County7 of 3420219.8%
Napa County8 of 345414.8%
Butte County9 of 343312.1%
Shasta County10 of 343312.1%
Yolo County34 of 34460.0%
Solano County33 of 34480.0%
Riverside County32 of 342420.8%
San Francisco County31 of 342542.4%
Sonoma County30 of 341003.0%
California's counties with 30 or more tests, by their own share at or above 4 pCi/L, 2005 to 2014, laboratory
ShareCountiesTheir testsFor example
50% or more00None
30% to 50%1303El Dorado County
15% to 30%6689Nevada County, Tulare County, Tuolumne County
5% to 15%196,774Napa County, Butte County, Shasta County
Under 5%81,966Orange County, San Bernardino County, San Diego County
California ten-year laboratory totals, pooled, against the United States
PeriodCountiesTestsAt or above 4 pCi/LUnited StatesChange from the row before
2008 to 2017569,41510.3%35.7%−0.3 points
2007 to 2016549,85410.6%35.8%−0.1 points
2006 to 2015549,58110.6%36.3%+0.7 points
2005 to 2014549,96910.0%36.0%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period. CDC publishes no state or national figure.

California, Counties

California counties by EPA zone

Predicted

All 58 counties, grouped by the zone EPA predicts and ordered by their reported share at or above 4 pCi/L, under California's map. Each county has a page of its own.

California radon map by county: EPA radon zones. Map of California's 58 counties shaded by EPA radon zone: Zone 1 in red-orange, Zone 2 in amber, Zone 3 in pale sand. 2 in Zone 1, 29 in Zone 2, 27 in Zone 3.
California radon map by countyEPA radon zones for California's counties: 2 counties in Zone 1, 29 counties in Zone 2, 27 counties in Zone 3.A prediction for each county, not a reading of any home; elevated homes occur in all three zones.

The 12 highest in California, 2005 to 2014

Zone 1: highest predicted potential2

Local help

California, Local resources

Local resources in California

Who to ask in California: its radon program, test kits and professionals.

What California's program says
Phone
1-800-745-7236
Email
Radonprogram@cdph.ca.gov
Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.

What it means

California, Questions

Questions about radon in California

Is radon a problem in California?

Of the 58 counties in California that EPA's Map of Radon Zones classifies, 2 carry Zone 1 (the highest predicted potential), 29 Zone 2 and 27 Zone 3. Pooled from 54 counties, 10.0% of the 9,969 radon tests reported to CDC over the 2005 to 2014 laboratory totals were at or above 4 pCi/L, 45th of 47 states.

Which California counties are in EPA radon Zone 1?

2 counties are in Zone 1: Santa Barbara County, Ventura County.

Who does radon mitigation in California?

Radon411's California directory lists 4 radon businesses for testing, mitigation or both, each with the licensing list it was read from.

Which California counties have the highest radon?

By the share of reported tests at or above 4 pCi/L, 2005 to 2014, laboratory: El Dorado County 33.3% (303 tests), Nevada County 28.9% (239 tests), Tulare County 27.2% (81 tests), Tuolumne County 24.6% (65 tests), Amador County 24.3% (37 tests).

Which EPA region is California in?

California is in EPA Region 9: Pacific Southwest.

Products

California, Products

Testing a home in California

10.0% of the 9,969 tests reported to CDC for California over the 2005 to 2014 laboratory totals reached 4 pCi/L: a short-term kit (2 to 90 days) gives a first answer in days, a long-term test the year-round average. A short-term kit (2 to 90 days) is the quick first check for a home in California; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for California homes, compared

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