Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Washington County, Rhode Island
EPA puts Washington County in Zone 1, its highest radon zone, and most reported tests there come back low, though 1.1% of 90 (2018) 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
1.1%
0.8 pts below RI
- Washington
- 1.1%
- RI
- 1.9%
90 tests, 2018
Median result
0.9pCi/L
Below action level
- Washington
- 0.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2018
Tests reported
90
2nd of 2 by tests
- Washington
- 90
- Providence
- 108
Reported to CDC before any fix, 2018
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in RI
2 of 2
Middle half
- Washington
- 1.1%
- Providence
- 1.9%
By share, of 2 with 30+ tests
Read a result for Washington County
Starts at Washington 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. Washington County's median reported result, 2018.
The data
Washington County, At a glance
Washington County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Washington County in
USGS geologic potential: High across 62% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Washington County, 2018
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 9.1% |
| 2015 | 0.0% |
| 2016 | 16.7% |
| 2017 | 1.4% |
| 2018 | 1.1% |
2018: 1.1%. Across these years the share ran from 0.0% to 16.7%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 90 tests reported to CDC for Washington County over 2018, 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: 2018. Measured data period: 2005 to 2018 (every CDC figure on file).
Washington County, Compared
Washington County radon figures, compared
Calculated by Radon411Only 1 of 90 radon tests reported for Washington County in 2018 reached 4 pCi/L (1.1%). The median result, 0.9 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 4.1 pCi/L.
Across 5 Rhode Island counties pooled together, 1.9% of tests reached that level, so Washington County runs 0.8 points below its state. Against the national pool of 29.1%, the gap is 28.0 points lower. Its place in the state: 2nd of 2 Rhode Island counties with 30 or more tests for the same period.
The reported tests do not follow EPA's Zone 1 label for Washington County (predicted average above 4 pCi/L): 1.1% of them reached 4 pCi/L, fewer than that label suggests. New London County, CT, the one bordering county with a figure for the same period, reported 60.5%.
Below the action level, 78 tests (86.7%) came in under 2 pCi/L, against 88.2% statewide, and 11 tests (12.2%) fell between 2 and 4, against 9.9% statewide. Over 3 years of annual figures the share fell 8.0 points, from 9.1% in 2014 to 1.1% in 2018; its peak was 9.1% in 2014. USGS geology rates 62% of the county's land high radon potential.
The busiest year on file was 2018, with 90 tests reported; the quietest, 2015, had 1.
Washington CountyRhode Island, pooled
| Year | Tests | Washington County, at or above 4 pCi/L | Rhode Island, pooled |
|---|---|---|---|
| 2014 | 88 | 9.1% | 2.4% |
| 2017 | 69 | 1.4% | 3.2% |
| 2018 | 90 | 1.1% | 1.9% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Washington County, Geology
The ground under Washington County
PredictedUSGS's geologic map splits Washington County: 61.6% of its land is high radon potential and 23.7% moderate and 13.1% low. The map puts 26.6% of Washington County in the area it calls Hope Valley Igneous Suite and 20.4% in Esmond-Dedham Subterrane, with 5 smaller areas beside them. USGS gives the first a radon index of 15, in the high band (12 to 17), and the second 11, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Hope Valley Igneous Suite | Granite gneiss and alaskite gneiss. | High | 15 | 26.6% |
| Esmond-Dedham Subterrane | Esmond granite, including fine-grained granite, granite, granodiorite, augen granite gneiss, and granite gneiss. | Moderate | 11 | 20.4% |
| Narragansett Pier Plutonic Suite | Granite (fine-grained, leucocratic, porphyritic). | High | 15 | 18.3% |
| Scituate Igneous Suite | Fine grained granite, alkali-feldspar granite, and granite. | High | 15 | 16.6% |
| Narragansett Bay Group | Sandstone, shale, and conglomerate with minor coal layers. Outwash sand and glacial lake deposits. | Low | 8 | 13.1% |
| Block Island | Block Island Moraine-Sandy and clayey till, beach and dune sand. | Moderate | 11 | 2.6% |
One smaller area is not listed. Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Washington County beside the ground around it
Washington County has more high-potential ground than Rhode Island as a whole: 61.6% of its land against 43.2%. Of the 2 counties that border it, 1 has more high-potential ground, Kent County the most at 75.5%.
The map rates the ground, not the air in any home.
Local help
Washington County, Local resources
Radon testing and mitigation in Washington County
- Radon Control ProgramRadon Control Program, run by Rhode Island Department of Health, licenses or certifies radon professionals, and answers questions about testing and mitigation in Rhode Island.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 Rhode Island36 professionals are listed in Rhode Island.
What Rhode Island's program says
- Licensing of radon professionals
This page lists Radon Testing businesses that are licensed by the Rhode Island Department of Health.
What it means
Washington County, Questions
Questions about radon in Washington County
Are radon levels high in Washington County?
In 2018, 1.1% of the radon tests reported to CDC for Washington County, Rhode Island were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.9 pCi/L. Of 2 Rhode Island counties with 30 or more tests for the same period, 1 reported a higher share; pooled, the state comes to 1.9%.
Which counties border Washington County?
Washington County borders 2 counties: Kent County, RI and New London County, CT.
Products
Washington County, Products
Testing a home in Washington County
In Washington County, 1.1% of 90 tests reported to CDC in 2018 reached 4 pCi/L, against 1.9% pooled across Rhode Island. In Zone 1 the year-round level in Washington 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 monitor
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
Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Washington County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Washington County
Explore
Washington County, Bordering counties
Counties bordering Washington County
Calculated by Radon411- Radon levels in New London County, CTEPA zone 1
60.5%at or above 4 pCi/L
Median 4.6 pCi/L · 200 tests · 59.4 points above Washington County
- Radon levels in Kent County, RIEPA zone 1
10.0%at or above 4 pCi/L
Median 0.8 pCi/L · 10 tests · 8.9 points above Washington County
Washington County, Residents
Who lives in Washington County
Washington County's population has barely moved since 2020: 129,795 residents on July 1, 2025 against 129,775 then, by the Census Bureau's estimates. That works out to 394 people per square mile of land. Testing is reported here more often than across the state: CDC's 90 reported tests for 2018 come to 0.7 for every 1,000 residents (2025 estimate), against 0.2 for Rhode Island.
Census lists no incorporated place in Washington County: every home in it reads the county's figures.
Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Washington County, Homes
Homes in Washington County
Washington County is a place of houses on their own lots: 77% of its 66,068 homes are detached single-family houses, against 55% across Rhode Island. Much of Washington County is recent building: 17% of its homes have gone up since 2000 and the middle year built is 1976, against 1961 for Rhode Island. Owners live in 77% of the occupied homes (Rhode Island: 63%), so for most households a test and a fix are their own to order.
| Homes | Washington County | Rhode Island |
|---|---|---|
| Housing units | 66,068 | 484,615 |
| Detached houses | 77% | 55% |
| In buildings of 5 or more | 9% | 17% |
| Mobile homes | 2% | 1% |
| Built before 1960 | 31% | 49% |
| Built since 2000 | 17% | 10% |
| Middle year built | 1976 | 1961 |
| Owner-occupied | 77% | 63% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.