Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
Locations and reports
Radon Levels in Santa Clara County, California
EPA puts Santa Clara County in Zone 2, its middle radon zone, and most reported tests there come back low, though 9.2% of 793 (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
Share at 4+ pCi/L
9.2%
1.1 pts below CA
- Santa Clara
- 9.2%
- California
- 10.3%
793 tests, 2008 to 2017
Median result
0.9pCi/L
Below action level
- Santa Clara
- 0.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
793
2nd of 33 by tests
- Santa Clara
- 793
- Los Angeles
- 2,363
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Rank in California
20 of 33
Middle half
- Santa Clara
- 9.2%
- El Dorado
- 30.3%
By share, of 33 with 30+ tests
Read a result for Santa Clara County
Starts at Santa Clara County's median, 0.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 0.9 pCi/L
Below 2 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Santa Clara County's median reported result, 2008 to 2017.
The data
Santa Clara County, At a glance
Santa Clara County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Santa Clara County is a
USGS geologic potential: Moderate across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Santa Clara County, 2008 to 2017, laboratory
Under 2 pCi/L: 76%2 to 4 pCi/L: 15%4 pCi/L and above: 9%
Of 793 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 598 | 75.4% |
| 2 to 4 pCi/L | 122 | 15.4% |
| 4 pCi/L and above | 73 | 9.2% |
What these figures count
These are the 793 tests reported to CDC for Santa Clara 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).
Santa Clara County, Compared
Santa Clara County radon figures, compared
Calculated by Radon411Santa Clara County reports fewer high tests than California overall. 9.2% of its 793 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 1.1 points below the 10.3% pooled from 56 California counties.
Ordered from highest share down, it comes 20th 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%; Santa Clara County sits 26.5 points below it.
Next door, the shares run from 6.7% in Alameda County to 21.9% in Santa Cruz County, with Alameda County below Santa Clara County. The reported tests do not follow EPA's Zone 2 label for Santa Clara County (predicted average between 2 and 4 pCi/L): 9.2% of them reached 4 pCi/L, fewer than that label suggests.
Half the tests came in under 0.9 pCi/L and half over it; the single highest reached 43.2 pCi/L. The rest split 75.4% under 2 pCi/L and 15.4% from 2 to 4 (California: 76.8% and 12.9%).
CDC's ten-year totals for Santa Clara County went from 701 tests (2005 to 2014) to 793 (2008 to 2017), the share going from 8.0% to 9.2%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Santa Clara County, Geology
The ground under Santa Clara County
PredictedUSGS's geologic map puts all of Santa Clara County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Southern Coast Ranges, to which USGS gives a radon index of 9, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Southern Coast Ranges | Metamorphosed 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. | Moderate | 9 | 99.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Santa Clara County beside the ground around it
Across California 0.1% of the land is rated high; none of Santa Clara County's is. Of the 7 counties that border it, 1 has more moderate-potential ground, San Benito County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Santa Clara County, Local resources
Radon testing and mitigation in Santa Clara County
Listed radon businesses with an address in Santa Clara County:
- California Indoor Radon ProgramCalifornia Indoor Radon Program, run by California Department of Public Health, licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in California.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Discounted test kits can be purchased through our partner laboratory, Alpha Energy, for $14.95.
- Compare kits
- Professionals in California4 professionals are listed in California.
Listed radon professionals by town: San Jose
What California's program says
- Phone
- 1-800-745-7236
- Radonprogram@cdph.ca.gov
- Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.
What it means
Santa Clara County, Questions
Questions about radon in Santa Clara County
Are radon levels high in Santa Clara County?
Over the 2008 to 2017 laboratory totals, 9.2% of the radon tests reported to CDC for Santa Clara County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.9 pCi/L. Of 33 California counties with 30 or more tests for the same period, 19 reported a higher share; pooled, the state comes to 10.3%.
Which counties border Santa Clara County?
Santa Clara County borders 7 counties: Santa Cruz County, San Mateo County, Alameda County, Stanislaus County, San Joaquin County, San Benito County and Merced County.
Products
Santa Clara County, Products
Testing a home in Santa Clara County
In Santa Clara County, 9.2% of 793 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 10.3% pooled across California. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Santa Clara County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
MonitorX-Sense
XR0A-iR Wi-Fi battery radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Wi-Fi
- Screen, app
Method: Alpha spectrometry
First reading: Within 24 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Santa Clara County, Bordering counties
Counties bordering Santa Clara County
Calculated by Radon411- Radon levels in Santa Cruz CountyEPA zone 2
21.9%at or above 4 pCi/L
Median 1.2 pCi/L · 105 tests · 12.7 points above Santa Clara County
- Radon levels in San Joaquin CountyEPA zone 3
14.9%at or above 4 pCi/L
Median 1.4 pCi/L · 74 tests · 5.7 points above Santa Clara County
- Radon levels in Stanislaus CountyEPA zone 3
11.1%at or above 4 pCi/L
Median 1.4 pCi/L · 27 tests · 1.9 points above Santa Clara County
- Radon levels in San Mateo CountyEPA zone 2
9.2%at or above 4 pCi/L
Median 0.9 pCi/L · 468 tests · 0.0 points above Santa Clara County
- Radon levels in Alameda CountyEPA zone 2
6.7%at or above 4 pCi/L
Median 0.7 pCi/L · 478 tests · 2.5 points below Santa Clara County
- Radon levels in San Benito CountyEPA zone 2
0.0%at or above 4 pCi/L
Median 0.7 pCi/L · 19 tests · 9.2 points below Santa Clara County
- Radon levels in Merced CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 2.1 pCi/L · 5 tests · 9.2 points below Santa Clara County
Santa Clara County, Cities and towns
Cities and towns in Santa Clara County
About 1,914,391 people live in Santa Clara County by the Census Bureau's estimate for July 1, 2025, 16,958 fewer than in 2020 (−0.9%). Packed into its land, that is 1,483 people per square mile. San Jose alone is home to 989,814 of them, 51.7% of the total. Together its 15 incorporated places hold 95.3% of those residents; the other 4.7% live outside any of them. Testing is reported here more often than across the state: CDC's 793 reported tests for 2008 to 2017 come to 0.4 for every 1,000 residents (2025 estimate), against 0.2 for California.
From San Jose to Monte Sereno, CDC publishes no figure by town: each reads Santa Clara County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| San Jose | 989,814 | −2.0% | 51.7% |
| Sunnyvale | 156,577 | +0.9% | 8.2% |
| Santa Clara | 133,446 | +3.8% | 7.0% |
| Mountain View | 85,438 | +3.2% | 4.5% |
| Milpitas | 78,596 | −1.5% | 4.1% |
| Palo Alto | 67,609 | −1.1% | 3.5% |
| Gilroy | 60,764 | +2.2% | 3.2% |
| Cupertino | 58,333 | −2.8% | 3.0% |
| Morgan Hill | 45,625 | −0.1% | 2.4% |
| Campbell | 42,490 | −3.0% | 2.2% |
| Los Gatos | 32,576 | −2.5% | 1.7% |
| Los Altos | 30,965 | −1.2% | 1.6% |
- Saratoga
- Los Altos Hills
- Monte Sereno
15 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).
Santa Clara County, Homes
Homes in Santa Clara County
Fewer than six in ten of Santa Clara County's 694,209 homes are detached houses (51%, against 57% across California); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1975, close to California's 1976: 22% date from before 1960 and 19% from 2000 or later. 55% 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 | Santa Clara County | California |
|---|---|---|
| Housing units | 694,209 | 14,532,683 |
| Detached houses | 51% | 57% |
| In buildings of 5 or more | 29% | 24% |
| Mobile homes | 3% | 4% |
| Built before 1960 | 22% | 27% |
| Built since 2000 | 19% | 18% |
| Middle year built | 1975 | 1976 |
| Owner-occupied | 55% | 56% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.