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Radon Levels in San Joaquin County, California

EPA puts San Joaquin County in Zone 3, its lowest radon zone, and most reported tests there come back low, though 14.9% of 74 (2008 to 2017, laboratory totals) reached 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

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  • Share at 4+ pCi/L

    14.9%

    4.6 pts above CA

    San Joaquin
    14.9%
    California
    10.3%

    74 tests, 2008 to 2017

  • Median result

    1.4pCi/L

    Below action level

    San Joaquin
    1.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    74

    26th of 33 by tests

    San Joaquin
    74
    Los Angeles
    2,363

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 3

    Lower potential

    1. 1
    2. 2
    3. Zone 3

    1 highest, 3 lowest

    EPA predicts under 2 pCi/L indoors

  • Rank in California

    11 of 33

    Middle half

    San Joaquin
    14.9%
    El Dorado
    30.3%

    By share, of 33 with 30+ tests

Read a result for San Joaquin County

Starts at San Joaquin County's median, 1.4 pCi/L

1.4pCi/L

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

EPA’s reading of 1.4 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. San Joaquin County's median reported result, 2008 to 2017.

Interpret this reading

The data

San Joaquin County, At a glance

San Joaquin County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for San Joaquin County as a whole is an average indoor of less than 2 pCi/L (less than 75 Bq/m³). A low zone clears no address in it: homes above EPA's turn up in all three zones.

USGS geologic potential: Low across 85% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for San Joaquin County, 2008 to 2017, laboratory

Reported results by concentration band, San Joaquin County, 2008 to 2017, laboratory
Under 2 pCi/L: 62%2 to 4 pCi/L: 23%4 pCi/L and above: 15%

Of 74 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, San Joaquin County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L4662.2%
2 to 4 pCi/L1723.0%
4 pCi/L and above1114.9%
What these figures count

These are the 74 tests reported to CDC for San Joaquin County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

San Joaquin County, Compared

San Joaquin County radon figures, compared

Calculated by Radon411

14.9% of its 74 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 4.6 points above the 10.3% pooled from 56 California counties.

Ordered from highest share down, it comes 11th of 33 California counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 35.7%; San Joaquin County sits 20.8 points below it.

Next door, the shares run from 6.7% in Alameda County to 27.8% in Amador County, with Santa Clara County, Contra Costa County and Sacramento County below San Joaquin County. Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 14.9% share point the same way here.

Half the tests came in under 1.4 pCi/L and half over it; the single highest reached 25.3 pCi/L. The rest split 62.2% under 2 pCi/L and 23.0% from 2 to 4 (California: 76.8% and 12.9%).

CDC's ten-year totals for San Joaquin County went from 65 tests (2005 to 2014) to 74 (2008 to 2017), the share going from 20.0% to 14.9%.

San Joaquin County against California, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from San Joaquin County
San Joaquin County7414.9%1.4 pCi/LThis county
California, pooled56 counties, pooled9,41510.3%Not pooled−4.6 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+20.8 points
El Dorado Countyhighest in the state27430.3%1.6 pCi/L+15.4 points
Sonoma Countylowest in the state1310.8%0.5 pCi/L−14.1 points
Amador County, CAborders it3627.8%2.3 pCi/L+12.9 points
Calaveras County, CAborders it3417.6%1.7 pCi/L+2.7 points
Stanislaus County, CAborders it2711.1%1.4 pCi/L−3.8 points
Santa Clara County, CAborders it7939.2%0.9 pCi/L−5.7 points
Contra Costa County, CAborders it2858.8%0.9 pCi/L−6.1 points
Sacramento County, CAborders it1947.7%0.9 pCi/L−7.2 points
Alameda County, CAborders it4786.7%0.7 pCi/L−8.2 points
Where San Joaquin County's reported results fell, 2008 to 2017, laboratory, beside California and the United States
ResultSan Joaquin County testsSan Joaquin County shareCalifornia shareU.S. shareAgainst California
Under 2 pCi/L4662.2%76.8%39.6%−14.6 points
2 to 4 pCi/L1723.0%12.9%24.7%+10.1 points
4 pCi/L and above1114.9%10.3%35.7%+4.6 points
San Joaquin County ranked among the 33 California counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Santa Cruz County6 of 3310521.9%1.2 pCi/L
Calaveras County7 of 333417.6%1.7 pCi/L
Santa Barbara County8 of 3342117.6%1.2 pCi/L
Solano County9 of 333815.8%0.9 pCi/L
Monterey County10 of 338714.9%0.8 pCi/L
San Joaquin County11 of 337414.9%1.4 pCi/L
Madera County12 of 333414.7%1.4 pCi/L
San Luis Obispo County13 of 338012.5%1.0 pCi/L
Ventura County14 of 3333511.9%1.0 pCi/L
Kern County15 of 3312111.6%1.8 pCi/L
Butte County16 of 333511.4%0.8 pCi/L
San Joaquin County ten-year laboratory totals, against California's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestCalifornia, pooledChange from the row before
2008 to 20177414.9%1.4 pCi/L25.3 pCi/L10.3%−1.0 points
2007 to 20166915.9%1.4 pCi/L25.3 pCi/L10.6%−3.5 points
2006 to 20156719.4%1.5 pCi/L25.3 pCi/L10.6%−0.6 points
2005 to 20146520.0%1.6 pCi/L25.3 pCi/L10.0%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

San Joaquin County, Geology

The ground under San Joaquin County

Predicted

Most of the ground under San Joaquin County is one class on USGS's geologic map: 84.6% of its land is low radon potential, with 15.0% moderate. The map puts 84.6% of San Joaquin County in the area it calls Great Valley and 8.3% in Southern Coast Ranges, with one smaller area beside them. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 9, in the moderate band (9 to 11).

USGS's geologic areas under San Joaquin County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Great ValleyQuaternary alluvial gravel, sand, silt, clay.Low884.6%
Southern Coast RangesMetamorphosed marine sedimentary rocks, ultramafic rocks, Triasic metamorphic rocks, Mesozoic granitic rocks, and a series of fault-bounded linear basins in which Teriary marine and continental sedimentary rocks were deposited.Moderate98.3%
Sierra NevadaNorthern Sierra Nevada is underlain primarily by Paleozoic and Mesozoic metamorphic rocks. Granitic rocks predominate in the southern Sierrra Nevada , with lesser Mesozoic metamorphic rocks.Moderate96.7%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

San Joaquin County beside the ground around it

Across California 0.1% of the land is rated high; none of San Joaquin County's is. Every one of the 7 counties that border it has more moderate-potential ground, Amador County the most at 100%.

Share of land by USGS radon potential: San Joaquin County, the 7 counties bordering it and California
AreaEPA zoneLow potentialModerate potentialHigh potential
San Joaquin CountyZone 384.6%15.0%None
Stanislaus CountyZone 349.1%50.9%None
Sacramento CountyZone 378.0%20.3%None
Calaveras CountyZone 2None100%None
Alameda CountyZone 20.8%98.5%None
Contra Costa CountyZone 221.8%74.1%None
Amador CountyZone 2None100%None
Santa Clara CountyZone 2None99.9%None
California58 counties, pooled by land areaVaries57.2%42.6%0.1%

The map rates the ground, not the air in any home.

Local help

San Joaquin County, Local resources

Radon testing and mitigation in San Joaquin County

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

San Joaquin County, Questions

Questions about radon in San Joaquin County

Are radon levels high in San Joaquin County?

Over the 2008 to 2017 laboratory totals, 14.9% of the radon tests reported to CDC for San Joaquin County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.4 pCi/L. Of 33 California counties with 30 or more tests for the same period, 10 reported a higher share; pooled, the state comes to 10.3%.

Which counties border San Joaquin County?

San Joaquin County borders 7 counties: Stanislaus County, Sacramento County, Calaveras County, Alameda County, Contra Costa County, Amador County and Santa Clara County.

Products

San Joaquin County, Products

Testing a home in San Joaquin County

In San Joaquin County, 14.9% of 74 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 10.3% pooled across California. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in San Joaquin County.

Test kits and monitors3

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Best radon monitors for San Joaquin County homes, compared

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San Joaquin County, Bordering counties

Counties bordering San Joaquin County

Calculated by Radon411

San Joaquin County, Cities and towns

Cities and towns in San Joaquin County

San Joaquin County is growing: the Census Bureau puts it at 823,815 residents on July 1, 2025, up 5.5% from 780,618 in 2020. That works out to 592 people per square mile of land. Its largest town, Stockton, has 324,597 residents, 39.4% of the total. Together its 7 incorporated places hold 79.9% of those residents; the other 20.1% live outside any of them. Reported testing is thin here: 74 tests over 2008 to 2017, or 0.1 for every 1,000 residents (2025 estimate), where California as a whole comes to 0.2.

From Stockton to Escalon, CDC publishes no figure by town: each reads San Joaquin County's.

The cities and towns in San Joaquin County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Stockton324,597+1.2%39.4%
Tracy101,901+8.8%12.4%
Manteca96,693+15.0%11.7%
Lodi69,100+4.0%8.4%
Lathrop42,783+46.9%5.2%
Ripon16,140+0.1%2.0%
Escalon7,394−1.1%0.9%

7 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).

San Joaquin County, Homes

Homes in San Joaquin County

Of San Joaquin County's 256,826 homes, 75% are detached houses, against 57% across California; 12% are in buildings of five or more homes. Half of its homes were built before 1983, close to California's 1976: 21% date from before 1960 and 27% from 2000 or later. 62% of occupied homes are lived in by their owner (California: 56%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in San Joaquin County, California, 2019 to 2023
HomesSan Joaquin CountyCalifornia
Housing units256,82614,532,683
Detached houses75%57%
In buildings of 5 or more12%24%
Mobile homes3%4%
Built before 196021%27%
Built since 200027%18%
Middle year built19831976
Owner-occupied62%56%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.