Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
Locations and reports
Radon Levels in San Diego County, California
EPA puts San Diego County in Zone 3, its lowest radon zone, and most reported tests there come back low, though 2.6% of 692 (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
2.6%
7.7 pts below CA
- San Diego
- 2.6%
- California
- 10.3%
692 tests, 2008 to 2017
Median result
0.2pCi/L
Below action level
- San Diego
- 0.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
692
3rd of 33 by tests
- San Diego
- 692
- Los Angeles
- 2,363
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Rank in California
30 of 33
Lowest quarter
- San Diego
- 2.6%
- El Dorado
- 30.3%
By share, of 33 with 30+ tests
Read a result for San Diego County
Starts at San Diego County's median, 0.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 0.2 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. San Diego County's median reported result, 2008 to 2017.
The data
San Diego County, At a glance
San Diego County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 99% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for San Diego County, 2008 to 2017, laboratory
Under 2 pCi/L: 92%2 to 4 pCi/L: 5%4 pCi/L and above: 3%
Of 692 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 639 | 92.3% |
| 2 to 4 pCi/L | 35 | 5.1% |
| 4 pCi/L and above | 18 | 2.6% |
What these figures count
These are the 692 tests reported to CDC for San Diego 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).
San Diego County, Compared
San Diego County radon figures, compared
Calculated by Radon411Only 18 of 692 radon tests reported for San Diego County over the 2008 to 2017 laboratory totals reached 4 pCi/L (2.6%). The median result, 0.2 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 45.2 pCi/L.
Across 56 California counties pooled together, 10.3% of tests reached that level, so San Diego County runs 7.7 points below its state. Against the national pool of 35.7%, the gap is 33.1 points lower. Its place in the state: 30th of 33 California counties with 30 or more tests for the same period.
Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 2.6% share point the same way here. Of 2 neighbours with a figure, 1 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 1.3% (Riverside County) to 3.9% (Orange County).
Below the action level, 639 tests (92.3%) came in under 2 pCi/L, against 76.8% statewide, and 35 tests (5.1%) fell between 2 and 4, against 12.9% statewide. USGS geology rates 99% of the county's land low radon potential.
CDC's ten-year totals for San Diego County went from 593 tests (2005 to 2014) to 692 (2008 to 2017), the share going from 3.0% to 2.6%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
San Diego County, Geology
The ground under San Diego County
PredictedUSGS's geologic map puts all of San Diego County's mapped land in one class: low radon potential. 96.7% of it lies in the area the map calls Peninsular Ranges, to which USGS gives a radon index of 7, in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Peninsular Ranges | Granite, metasedimentary and metavolcanic rocks, marine sedimentary rocks, and coastal sediments. | Low | 7 | 96.7% |
| Colorado Desert | Pleistocene to Holocene marine and (mostly) nonmarine gravel, sand, silt, and clay deposits. | Low | 8 | 2.8% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
San Diego County beside the ground around it
Across California 0.1% of the land is rated high; none of San Diego County's is. Of the 3 counties that border it, 1 has more moderate-potential ground, Riverside County the most at 4.2%.
The map rates the ground, not the air in any home.
Local help
San Diego County, Local resources
Radon testing and mitigation in San Diego 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.
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
San Diego County, Questions
Questions about radon in San Diego County
Are radon levels high in San Diego County?
Over the 2008 to 2017 laboratory totals, 2.6% of the radon tests reported to CDC for San Diego County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.2 pCi/L. Of 33 California counties with 30 or more tests for the same period, 29 reported a higher share; pooled, the state comes to 10.3%.
Which counties border San Diego County?
San Diego County borders 3 counties: Riverside County, Orange County and Imperial County.
Products
San Diego County, Products
Testing a home in San Diego County
In San Diego County, 2.6% of 692 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 Diego County.
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
MonitorAEGTEST
HOUND-1011S rechargeable radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 12 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
San Diego County, Bordering counties
Counties bordering San Diego County
Calculated by Radon411- Radon levels in Orange CountyEPA zone 3
3.9%at or above 4 pCi/L
Median 0.7 pCi/L · 431 tests · 1.3 points above San Diego County
- Radon levels in Riverside CountyEPA zone 2
1.3%at or above 4 pCi/L
Median 0.6 pCi/L · 226 tests · 1.3 points below San Diego County
- Radon levels in Imperial CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 0.6 pCi/L · 11 tests · 2.6 points below San Diego County
San Diego County, Cities and towns
Cities and towns in San Diego County
About 3,282,248 people live in San Diego County by the Census Bureau's estimate for July 1, 2025, 18,862 fewer than in 2020 (−0.6%). That works out to 780 people per square mile of land. Its largest town, San Diego, has 1,406,106 residents, 42.8% of the total. Together its 18 incorporated places hold 84.8% of those residents; the other 15.2% live outside any of them. CDC's 692 reported tests for 2008 to 2017 work out to 0.2 per 1,000 residents (2025 estimate), close to California's 0.2.
From San Diego to Del Mar, CDC publishes no figure by town: each reads San Diego County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| San Diego | 1,406,106 | +1.7% | 42.8% |
| Chula Vista | 275,533 | −0.1% | 8.4% |
| Oceanside | 170,483 | −2.1% | 5.2% |
| Escondido | 146,030 | −3.3% | 4.4% |
| Carlsbad | 112,260 | −2.3% | 3.4% |
| El Cajon | 101,755 | −4.1% | 3.1% |
| Vista | 98,274 | −0.6% | 3.0% |
| San Marcos | 94,908 | Level | 2.9% |
| Encinitas | 60,736 | −2.0% | 1.9% |
| La Mesa | 59,914 | −1.9% | 1.8% |
| Santee | 58,205 | −2.8% | 1.8% |
| National City | 57,807 | −5.9% | 1.8% |
- Poway
- Lemon Grove
- Imperial Beach
- Coronado
- Solana Beach
- Del Mar
18 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 Diego County, Homes
Homes in San Diego County
Fewer than six in ten of San Diego County's 1,240,607 homes are detached houses (50%, against 57% across California); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1980, close to California's 1976: 17% 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 | San Diego County | California |
|---|---|---|
| Housing units | 1,240,607 | 14,532,683 |
| Detached houses | 50% | 57% |
| In buildings of 5 or more | 29% | 24% |
| Mobile homes | 4% | 4% |
| Built before 1960 | 17% | 27% |
| Built since 2000 | 19% | 18% |
| Middle year built | 1980 | 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.