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Radon in San Antonio, Texas

San Antonio lies in 3 counties, in EPA Zone 3; 99.9% of it is in Bexar County, where 6.5% of 201 reported tests (2008 to 2017, laboratory totals) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so the only way to know your home's level is to test it.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    6.5%

    3.7 pts below TX

    Bexar
    6.5%
    Texas
    10.2%

    Bexar, 11th of 22 in TX, 2008 to 2017

  • Median result

    0.6pCi/L

    Below action level

    Bexar
    0.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of Bexar's tests, 2008 to 2017

  • Nearest county

    9.2%

    Travis, 75 miles

    Travis
    9.2%
    Bexar
    6.5%

    426 tests, 2008 to 2017

  • EPA radon zone

    Zone 3

    Low potential

    1. 1
    2. 2
    3. Zone 3

    1 highest, 3 lowest

    Bexar; Medina Zone 3, Comal Zone 3

  • Tests reported

    201

    In Bexar

    Bexar
    201
    Travis
    426

    Reported to CDC before any fix, 2008 to 2017

Read a result for San Antonio

Starts at Bexar County's median, 0.6 pCi/L

0.6pCi/L

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

EPA’s reading of 0.6 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. Bexar County's median reported result, 2008 to 2017.

Interpret this reading

The data

San Antonio, What is published

What is published for San Antonio

Information:

Every figure for San Antonio is a county's

Radon data is published by county, not by city, and San Antonio reaches into 3 counties: Bexar County, Medina County and Comal County. Each has its own EPA zone and its own CDC test figures, set side by side below and each labelled with its county. Only a test tells you about one home.

San Antonio covers 499 square miles of land: 99.9% of it lies in Bexar County and 0.1% in Medina County. About 1,548,422 people live there, 3,104 to the square mile.

San Antonio, Counties

San Antonio's counties, side by side

Measured

Each county's own EPA zone and its own published CDC figures for 2008 to 2017, laboratory, the newest period any of them has. A county without a figure for that period is shown without one, never with a figure from another year.

  • Bexar County
    EPA zone
    Zone 3: Lower predicted potential
    At or above 4 pCi/L
    6.5%
    Median result
    0.6 pCi/L
    Tests reported
    201 tests
    Annual years on file
    None
  • Medina County
    EPA zone
    Zone 3: Lower predicted potential
    At or above 4 pCi/L
    0.0%
    Median result
    0.5 pCi/L
    Tests reported
    2 tests
    Annual years on file
    None
  • Comal County
    EPA zone
    Zone 3: Lower predicted potential
    At or above 4 pCi/L
    4.5%
    Median result
    0.9 pCi/L
    Tests reported
    22 tests
    Annual years on file
    None
The counties San Antonio lies in, each with its own EPA zone and its own published CDC figures for 2008 to 2017, laboratory
CountyEPA zoneReported tests at or above 4 pCi/LMedian reported resultTests reportedAnnual years on file
Bexar CountyZone 3: Lower predicted potential6.5%0.6 pCi/L201 testsNone
Medina CountyZone 3: Lower predicted potential0.0%0.5 pCi/L2 testsNone
Comal CountyZone 3: Lower predicted potential4.5%0.9 pCi/L22 testsNone

San Antonio spans 3 counties, each with its own EPA zone and its own CDC figure: Bexar County (Zone 3, 6.5% of 201 tests), Medina County (Zone 3, 0.0% of 2 tests) and Comal County (Zone 3, 4.5% of 22 tests).

Bexar County ranks 11th of 22 Texas counties with 30 or more tests for that period, 3.7 points below the 10.2% pooled across Texas's counties, 29.2 points below the national pool of 35.7%. Of the city's other counties, Medina County reported 0.0% and Comal County reported 4.5%.

Measured from the middle of San Antonio, the nearest counties with a CDC figure for 2008 to 2017, laboratory are Travis County (75 miles, 9.2% of 426 tests), Williamson County (99 miles, 1.9% of 103 tests) and Bell County (125 miles, 16.7% of 30 tests). Across the 8 nearest, the share at or above 4 pCi/L runs from 0.0% to 23.3%; the farthest of them, Brazoria County, is 186 miles away at 6.3%.

No business in the directory gives San Antonio as its address; the Texas list covers it. Texas's other cities with a page of their own: Austin and Houston.

Against Texas and its other counties

Radon test figures for the county San Antonio lies in
CountyShare of San AntonioTestsAt or above 4 pCi/LMedianTexas, pooledRank in the stateEPA zone
Bexar County99.9%2016.5%0.6 pCi/L10.2%11 of 22Zone 3

Shares of tests people chose to run and report, by county (2008 to 2017, laboratory); the state's is its counties' counts added up, calculated by Radon411. Only a test measures a home.

The counties around San Antonio

By distance from the middle of San Antonio; counties with 30 or more tests.

Nearest counties to San Antonio with 30 or more tests
CountyDistanceTestsAt or above 4 pCi/LMedian
Travis County75 mi4269.2%0.9 pCi/L
Williamson County99 mi1031.9%0.7 pCi/L
Bell County125 mi3016.7%1.3 pCi/L
Nueces County132 mi430.0%0.6 pCi/L
Brazos County157 mi470.0%0.5 pCi/L
McLennan County164 mi3023.3%1.1 pCi/L
Fort Bend County166 mi1052.9%0.2 pCi/L
Brazoria County186 mi326.3%0.3 pCi/L

The median reported pre-mitigation result for 2008 to 2017, laboratory was 0.6 pCi/L in Bexar County, 0.5 pCi/L in Medina County and 0.9 pCi/L in Comal County.

Predicted: EPA Map of Radon Zones, by county. Measured: CDC tracking data, by county, 2008 to 2017, laboratory.

San Antonio, Geology

The ground under San Antonio

Predicted

USGS's geologic map puts all of San Antonio's mapped land in one class: low radon potential. The map puts 86.5% of San Antonio in the area it calls East Texas Province and 13.5% in Southern High Plains and Plateaus. USGS gives the first a radon index of 6 and the second 7, both in the low band (5 to 8).

USGS's geologic areas under San Antonio
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
East Texas ProvinceCretaceous through Quaternary marine sandstone, shale, chalk, limestone, siltstone, clay, and lignite.Low686.5%
Southern High Plains and PlateausPaleozoic and Mesozoic sandstone, limestone, shale.Low713.5%

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

San Antonio beside its counties and Texas

Neither San Antonio nor Bexar County as a whole has any land USGS rates above low potential. Across Texas 0.5% of the land is rated high; none of San Antonio's is.

Share of land by USGS radon potential: San Antonio, the counties it lies in and Texas
AreaEPA zoneLow potentialModerate potentialHigh potential
San AntonioBy county100%NoneNone
Bexar CountyZone 3100%NoneNone
Medina CountyZone 3100%NoneNone
Comal CountyZone 3100%NoneNone
Texas254 counties, pooled by land areaVaries72.4%26.8%0.5%

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

San Antonio, Homes

Homes in San Antonio

Of San Antonio's 603,213 homes, 59% are detached houses, against 65% across Bexar County; 29% are in buildings of five or more homes. Half of its homes were built before 1984, close to Bexar County's 1989: 20% date from before 1960 and 29% from 2000 or later. 52% of occupied homes are lived in by their owner (Bexar County: 59%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in San Antonio, Bexar County, Texas, 2019 to 2023
HomesSan AntonioBexar CountyTexas
Housing units603,213807,16011,890,808
Detached houses59%65%65%
In buildings of 5 or more29%24%21%
Mobile homes2%3%7%
Built before 196020%16%13%
Built since 200029%37%37%
Middle year built198419891990
Owner-occupied52%59%63%

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

Local help

San Antonio, Local resources

Local resources for San Antonio

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

The program's own words on licensing are on the Texas page.

What it means

San Antonio, Questions

Questions about radon in San Antonio

What radon zone is San Antonio in?

All 3 counties San Antonio reaches into (Bexar County, Medina County and Comal County) are in Zone 3, the map's lowest class: a predicted county average under 2 pCi/L. EPA zones counties, not cities, so that is the zone for every part of San Antonio.

What are radon levels in San Antonio?

Reported levels around San Antonio run low: 6.5% of 201 tests from Bexar County for 2008 to 2017 (laboratory totals) reached 4 pCi/L. The median reported result was 0.6 pCi/L. Low is not none. Medina County reported 0.0% of 2 tests and Comal County reported 4.5% of 22 tests; the counties are kept apart.

Should I test my home in San Antonio?

Yes, even here. Bexar County reported 13 of 201 tests at or above 4 pCi/L. That is below Texas' pooled 10.2%, and still not a reason to skip it, and ranks Bexar County 11th of the 22 Texas counties with 30 or more tests. Testing found those homes; the county's low share did not. How to test a home.

What ground is San Antonio built on, as far as radon goes?

86.5% of San Antonio sits on what USGS's map calls "East Texas Province", rated low for radon potential, radon index 6; another 13.5% is "Southern High Plains and Plateaus", in the same class.

Is radon higher in the counties around San Antonio?

It depends which way you go. 3 of the 8 nearest counties with a figure report a larger share than Bexar County's 6.5% and 5 a smaller one: from Nueces County (0.0%, 132 miles off) to McLennan County (23.3%, 164 miles off).

The answers use the published figures of Bexar County, Medina County and Comal County, the counties San Antonio lies in.

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