Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Fairfax County, Virginia
EPA puts Fairfax County in Zone 1, its highest radon zone, and 18.7% of its 8,657 reported radon tests (2008 to 2017, laboratory totals) were at or above 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
18.7%
11.7 pts below VA
- Fairfax
- 18.7%
- Virginia
- 30.4%
8,657 tests, 2008 to 2017
Median result
1.5pCi/L
Below action level
- Fairfax
- 1.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
8,657
Most tested in Virginia
- Fairfax
- 8,657
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Virginia
73 of 84
Lowest quarter
- Fairfax
- 18.7%
- Russell
- 67.3%
By share, of 84 with 30+ tests
Read a result for Fairfax County
Starts at Fairfax County's median, 1.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.5 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. Fairfax County's median reported result, 2008 to 2017.
The data
Fairfax County, At a glance
Fairfax County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Fairfax County in
USGS geologic potential: High across 61% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Fairfax County, 2008 to 2017, laboratory
Under 2 pCi/L: 59%2 to 4 pCi/L: 22%4 pCi/L and above: 19%
Of 8,657 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 5,103 | 58.9% |
| 2 to 4 pCi/L | 1,931 | 22.3% |
| 4 pCi/L and above | 1,623 | 18.7% |
What these figures count
These are the 8,657 tests reported to CDC for Fairfax 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).
Fairfax County, Compared
Fairfax County radon figures, compared
Calculated by Radon411Fairfax County's 8,657 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.5 pCi/L and a maximum of 96.5 pCi/L, and 18.7% reached 4 pCi/L. Virginia as a whole (131 Virginia counties, pooled) comes to 30.4%: 11.7 points higher than here.
Among its state's counties it ranks 73rd of 84 Virginia counties with 30 or more tests for the same period. Statewide for the same period, Russell County reported the highest share (67.3%) and Norfolk city the lowest (2.7%).
Below the action level, 5,103 tests (58.9%) came in under 2 pCi/L, against 44.7% statewide, and 1,931 tests (22.3%) fell between 2 and 4, against 24.9% statewide. CDC's ten-year totals for Fairfax County went from 6,409 tests (2005 to 2014) to 8,657 (2008 to 2017), the share going from 17.9% to 18.7%.
EPA's 1993 zone map puts Fairfax County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 61% of the county's land high radon potential.
Next door, the shares run from 7.3% in Alexandria city to 31.7% in Prince William County, with Montgomery County, MD, Fairfax city and Arlington County below Fairfax County.
CDC also counts 653 tests taken after mitigation in Fairfax County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Fairfax County, Geology
The ground under Fairfax County
PredictedUSGS's geologic map splits Fairfax County: 61.1% of its land is high radon potential and 12.7% moderate and 25.2% low. The map puts 61.0% of Fairfax County in the area it calls Inner Piedmont and 25.2% in Cretaceous Coastal Plain Sediments, with one smaller area beside them. USGS gives the first a radon index of 12, in the high band (12 to 17), and the second 8, in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Inner Piedmont | Granite, pegmatites, granitic gneiss, schist and gneiss, slate, and phyllite. | High | 12 | 61.0% |
| Cretaceous Coastal Plain Sediments | Cretaceous Coastal Plain sand, silt, clay. | Low | 8 | 25.2% |
| Mesozoic Basins | Sandstone, siltstone and lacustrine black shale. | Moderate | 11 | 12.7% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Fairfax County beside the ground around it
Fairfax County has more high-potential ground than Virginia as a whole: 61.1% of its land against 47.9%. Of the 10 counties that border it, 3 have more high-potential ground, Fairfax city the most at 100%.
The map rates the ground, not the air in any home.
Local help
Fairfax County, Local resources
Radon testing and mitigation in Fairfax County
- VDH Radon ProgramVDH Radon Program answers questions about testing, mitigation and the rules in Virginia.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsAsk the program whether it has free or discounted kits, or compare kits you can buy.
- Compare kits
- Professionals in Virginia2 professionals are listed in Virginia.
What Virginia's program says
- Phone
- (804) 864-8161
- Radon@vdh.virginia.gov
- Licensing of radon professionals
The Code of Virginia requires that Radon testers and mitigators be currently certified by either the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB).
What it means
Fairfax County, Questions
Questions about radon in Fairfax County
Are radon levels high in Fairfax County?
Over the 2008 to 2017 laboratory totals, 18.7% of the radon tests reported to CDC for Fairfax County, Virginia were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.5 pCi/L. Of 84 Virginia counties with 30 or more tests for the same period, 72 reported a higher share; pooled, the state comes to 30.4%.
Which counties border Fairfax County?
Fairfax County borders 10 counties: Manassas Park city, VA, Fairfax city, VA, Prince William County, VA, Arlington County, VA, Alexandria city, VA, District of Columbia, DC, Loudoun County, VA, Montgomery County, MD, Prince George's County, MD and Charles County, MD.
Products
Fairfax County, Products
Testing a home in Fairfax County
In Fairfax County, 18.7% of 8,657 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 30.4% pooled across Virginia. In Zone 1 the year-round level in Fairfax County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitorMonitorSafetySiren
Pro4 plug-in radon detector with a display and alarm
- C-NRPP 2024/25: Not included
- Plug-in
- Alarm
- Screen
First reading: Within 48 hours
Short-term kit
Radon Short Term Test Kit short-term charcoal radon test kit, lab fee included
- Lab fee included
Method: Charcoal
In home: 2 to 7 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Fairfax County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Fairfax County
Explore
Fairfax County, Bordering counties
Counties bordering Fairfax County
Calculated by Radon41131.7%at or above 4 pCi/L
Median 2.3 pCi/L · 4,441 tests · 13.0 points above Fairfax County
- Radon levels in Loudoun County, VAEPA zone 2
27.4%at or above 4 pCi/L
Median 1.8 pCi/L · 4,457 tests · 8.7 points above Fairfax County
- Radon levels in Charles County, MDEPA zone 2
24.1%at or above 4 pCi/L
Median 1.8 pCi/L · 477 tests · 5.4 points above Fairfax County
- Radon levels in Manassas Park city, VAEPA zone 1
20.0%at or above 4 pCi/L
Median 1.4 pCi/L · 25 tests · 1.3 points above Fairfax County
19.0%at or above 4 pCi/L
Median 1.4 pCi/L · 1,603 tests · 0.3 points above Fairfax County
- Radon levels in Montgomery County, MDEPA zone 1
18.0%at or above 4 pCi/L
Median 1.3 pCi/L · 10,969 tests · 0.7 points below Fairfax County
- Radon levels in Fairfax city, VAEPA zone 1
14.3%at or above 4 pCi/L
Median 1.4 pCi/L · 126 tests · 4.4 points below Fairfax County
- Radon levels in Arlington County, VAEPA zone 2
13.7%at or above 4 pCi/L
Median 1.4 pCi/L · 1,101 tests · 5.0 points below Fairfax County
- Radon levels in District of Columbia, DCEPA zone 3
8.7%at or above 4 pCi/L
Median 1.2 pCi/L · 2,126 tests · 10.0 points below Fairfax County
- Radon levels in Alexandria city, VAEPA zone 3
7.3%at or above 4 pCi/L
Median 1.0 pCi/L · 410 tests · 11.4 points below Fairfax County
Fairfax County, Cities and towns
Cities and towns in Fairfax County
The Census Bureau estimates 1,167,873 residents in Fairfax County for July 1, 2025, 19,275 more than in 2020 (+1.7%). Packed into its land, that is 2,987 people per square mile. Herndon, the largest place on its list (25,506 residents in all), extends beyond Fairfax County, so no share of the total is worked out for it. CDC's 8,657 reported tests for 2008 to 2017 work out to 7.4 per 1,000 residents (2025 estimate), close to Virginia's 6.0.
From Herndon to Clifton, CDC publishes no figure by town: each reads Fairfax County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Herndonextends beyond Fairfax County | 25,506 | +3.7% | Counted whole |
| Vienna | 16,691 | +1.5% | 1.4% |
| Occoquanextends beyond Fairfax County | 1,078 | +4.1% | Counted whole |
| Clifton | 241 | +0.4% | Under 0.1% |
4 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). A place that extends beyond Fairfax County is counted whole, so it has no share.
Fairfax County, Homes
Homes in Fairfax County
Fewer than six in ten of Fairfax County's 428,352 homes are detached houses (46%, against 61% across Virginia); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1983, close to Virginia's 1984: 11% date from before 1960 and 19% from 2000 or later. 68% of occupied homes are lived in by their owner (Virginia: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Fairfax County | Virginia |
|---|---|---|
| Housing units | 428,352 | 3,654,784 |
| Detached houses | 46% | 61% |
| In buildings of 5 or more | 29% | 19% |
| Mobile homes | under 1% | 4% |
| Built before 1960 | 11% | 19% |
| Built since 2000 | 19% | 25% |
| Middle year built | 1983 | 1984 |
| Owner-occupied | 68% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.