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Radon Levels in Adams County, Colorado

EPA puts Adams County in Zone 1, its highest radon zone, and 36.6% of its 1,191 reported radon tests (2023) 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    36.6%

    2.3 pts below CO

    Adams
    36.6%
    Colorado
    38.9%

    1,191 tests, 2023

  • Median result

    2.3pCi/L

    Below action level

    Adams
    2.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    1,191

    8th of 38 by tests

    Adams
    1,191
    Jefferson
    3,068

    Reported to CDC before any fix, 2023

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Colorado

    26 of 38

    Middle half

    Adams
    36.6%
    Park
    57.5%

    By share, of 38 with 30+ tests

Read a result for Adams County

Starts at Adams County's median, 2.3 pCi/L

2.3pCi/L

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

EPA’s reading of 2.3 pCi/L

Between 2 and 4 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 between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Adams County's median reported result, 2023.

Interpret this readingWhat a fix costs

The data

Adams County, At a glance

Adams County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Adams County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Adams County, 2023

Share of reported tests at or above 4 pCi/L, by year, Adams County
Share of reported tests at or above 4 pCi/L, by year, Adams County
YearShare of reported tests at or above 4 pCi/L
201443.0%
201543.5%
201636.7%
201735.4%
201845.7%
201939.5%
202038.8%
202143.0%
202237.9%
202336.6%

2023: 36.6%. Across these years the share ran from 35.4% to 45.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 1,191 tests reported to CDC for Adams County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Adams County, Compared

Adams County radon figures, compared

Calculated by Radon411

In Adams County, about 4 in 10 reported tests in 2023 (436 of 1,191) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 3.2 points higher. Across 61 Colorado counties pooled together, 38.9% of tests reached that level, so Adams County runs 2.3 points below its state.

Of 6 neighbours with a figure, 5 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 35.4% (Denver County) to 50.0% (Morgan County). By share, Adams County is 26th of 38 Colorado counties with 30 or more tests for the same period.

Year by year, 2014 opened at 43.0% and 2023 closed at 36.6% (down 6.4 points), with 2018 the high at 45.7%. Half the tests came in under 2.3 pCi/L and half over it; the single highest reached 96.4 pCi/L. Below the action level, 552 tests (46.3%) came in under 2 pCi/L, against 39.2% statewide, and 203 tests (17.0%) fell between 2 and 4, against 22.0% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 36.6% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 276 tests taken after mitigation in Adams County for the same period: tests in homes where a fix was already in.

The busiest year on file was 2019, with 1,978 tests reported; the quietest, 2014, had 456.

Share of reported tests at or above 4 pCi/L by year, Adams County against Colorado2014 to 2023, years with 30 or more tests: Adams County 43.0% to 36.6%, the state's pooled share 38.9% in 2023.
Adams CountyColorado, pooled
Share of reported tests at or above 4 pCi/L by year, Adams County against Colorado: data table
YearTestsAdams County, at or above 4 pCi/LColorado, pooled
201445643.0%46.5%
201555643.5%47.2%
201661136.7%38.5%
201774935.4%41.0%
20181,94145.7%44.2%
20191,97839.5%44.1%
20201,40838.8%41.9%
20211,61643.0%47.3%
20221,83337.9%38.6%
20231,19136.6%38.9%
Adams County against Colorado, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Adams County
Adams County1,19136.6%2.3 pCi/LThis county
Colorado, pooled61 counties, pooled21,80238.9%Not pooled+2.3 points
United States, pooled642 counties, pooled128,74033.4%Not pooled−3.2 points
Park Countyhighest in the state10657.5%4.6 pCi/L+20.9 points
Bent Countylowest in the state1083.7%0.1 pCi/L−32.9 points
Washington County, COborders it2100.0%5.3 pCi/L+63.4 points
Morgan County, COborders it3850.0%4.0 pCi/L+13.4 points
Weld County, COborders it66346.0%3.5 pCi/L+9.4 points
Jefferson County, COborders it3,06841.8%3.2 pCi/L+5.2 points
Arapahoe County, COborders it1,99037.9%2.5 pCi/L+1.3 points
Broomfield County, COborders it75836.9%2.3 pCi/L+0.3 points
Denver County, COborders it2,27735.4%2.8 pCi/L−1.2 points
Where Adams County's reported results fell, 2023, beside Colorado and the United States
ResultAdams County testsAdams County shareColorado shareU.S. shareAgainst Colorado
Under 2 pCi/L55246.3%39.2%41.4%+7.1 points
2 to 4 pCi/L20317.0%22.0%25.2%−5.0 points
4 pCi/L and above43636.6%38.9%33.4%−2.3 points
Adams County ranked among the 38 Colorado counties with 30 or more tests, by share at or above 4 pCi/L, 2023
CountyRankTestsAt or above 4 pCi/LMedian
La Plata County20 of 3822439.3%3.1 pCi/L
Summit County22 of 3829538.3%2.0 pCi/L
Arapahoe County23 of 381,99037.9%2.5 pCi/L
Ouray County24 of 384337.2%1.2 pCi/L
Broomfield County25 of 3875836.9%2.3 pCi/L
Adams County26 of 381,19136.6%2.3 pCi/L
Pitkin County27 of 3816436.6%2.5 pCi/L
Douglas County28 of 381,63535.8%2.4 pCi/L
Denver County29 of 382,27735.4%2.8 pCi/L
Gunnison County30 of 3814734.7%2.5 pCi/L
El Paso County31 of 381,84434.4%2.5 pCi/L
Adams County radon tests by year, against Colorado's pooled share
YearTestsAt or above 4 pCi/LMedianHighestColorado, pooledChange from the row before
20231,19136.6%2.3 pCi/L96.4 pCi/L38.9%−1.3 points
20221,83337.9%2.5 pCi/L107.6 pCi/L38.6%−5.1 points
20211,61643.0%3.0 pCi/L279.0 pCi/L47.3%+4.2 points
20201,40838.8%2.6 pCi/L55.9 pCi/L41.9%−0.7 points
20191,97839.5%2.8 pCi/L183.3 pCi/L44.1%−6.2 points
20181,94145.7%3.5 pCi/L58.8 pCi/L44.2%+10.3 points
201774935.4%2.5 pCi/L102.1 pCi/L41.0%−1.3 points
201661136.7%2.4 pCi/L54.0 pCi/L38.5%−6.8 points
201555643.5%3.5 pCi/L42.4 pCi/L47.2%+0.5 points
201445643.0%3.4 pCi/L207.2 pCi/L46.5%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Adams County, State data

Colorado's own radon test data

Measured

What Colorado's own agencies publish about radon tests in Adams County, with their period. These are not CDC's figures and are never added to them.

MeasuredState figures, not CDC's

What Colorado CDPHE reports for Adams County

Radon data (county results): radon test results received from radon testing labs, primarily short-term household tests taken by the homeowner. Period: 2005-2025.

Share over 4 pCi/L

46.5%

5,760 of 12,383 tests

Median result

3.5 pCi/L

Highest result

279.0 pCi/L

Tests behind these figures

12,383 tests

  • CDPHE says these data do not give actual radon levels in homes that have not been tested.
  • When possible, only tests conducted before a mitigation system was installed are used.
  • Some counties have very small numbers of test results, and their summaries may be less representative.
  • These figures describe tests reported to Colorado CDPHE in this area. They count a different set of tests than CDC's figures and are not a reading of any one home.

Measured: Colorado CDPHE data, 2005-2025.

Adams County, Geology

The ground under Adams County

Predicted

USGS's geologic map puts all of Adams County's mapped land in one class: high radon potential. 95.7% of it lies in the area the map calls High Plains, to which USGS gives a radon index of 12, in the high band (12 to 17).

USGS's geologic areas under Adams County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
High PlainsQuaternary deposits and Cretaceous marine shales that locally have a high radiometric signature.High1295.7%
Dawson ArkoseConsolidated alluvial fan and river deposits sourced in the granite mountains to the west.High144.3%

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

Adams County beside the ground around it

Adams County has more high-potential ground than Colorado as a whole: 100% of its land against 74.8%. Of the 7 counties that border it, none has as large a share of high-potential ground; Arapahoe County comes nearest at 100%.

Share of land by USGS radon potential: Adams County, the 7 counties bordering it and Colorado
AreaEPA zoneLow potentialModerate potentialHigh potential
Adams CountyZone 1NoneNone100%
Arapahoe CountyZone 1NoneNone100%
Morgan CountyZone 1NoneNone100%
Denver CountyZone 1NoneNone100%
Weld CountyZone 1None33.9%66.2%
Broomfield CountyZone 1NoneNone100%
Washington CountyZone 1None9.6%90.4%
Jefferson CountyZone 1NoneNone100%
Colorado64 counties, pooled by land areaVariesNone25.2%74.8%

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

Local help

Adams County, Local resources

Radon testing and mitigation in Adams County

Listed radon professionals by town: Westminster

What Colorado's program says
Licensing of radon professionals
Listed contractors are certified by the National Radon Proficiency Program or the National Radon Safety Board, and must be licensed by the Colorado Department of Regulatory Agencies.
Disclosure when a home is sold or rented
As of August 7, 2023, landlords in Colorado are required to disclose radon information when a tenant signs a lease agreement.

What it means

Adams County, Questions

Questions about radon in Adams County

Are radon levels high in Adams County?

In 2023, 36.6% of the radon tests reported to CDC for Adams County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.3 pCi/L. Of 38 Colorado counties with 30 or more tests for the same period, 25 reported a higher share; pooled, the state comes to 38.9%.

Which counties border Adams County?

Adams County borders 7 counties: Arapahoe County, Morgan County, Denver County, Weld County, Broomfield County, Washington County and Jefferson County.

Products

Adams County, Products

Testing a home in Adams County

In Adams County, 36.6% of 1,191 tests reported to CDC in 2023 reached 4 pCi/L, against 38.9% pooled across Colorado. In Zone 1 the year-round level in Adams 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

Adams County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Adams County

Explore

Adams County, Bordering counties

Counties bordering Adams County

Calculated by Radon411

Adams County, Cities and towns

Cities and towns in Adams County

Adams County is growing: the Census Bureau puts it at 554,668 residents on July 1, 2025, up 6.6% from 520,411 in 2020. That works out to 475 people per square mile of land. Aurora, the largest place on its list (410,053 residents in all), extends beyond Adams County, so no share of the total is worked out for it. Reported testing is thin here: 1,191 tests over 2023, or 2.1 for every 1,000 residents (2025 estimate), where Colorado as a whole comes to 3.6.

From Aurora to Bennett, CDC publishes no figure by town: each reads Adams County's.

The cities and towns in Adams County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Auroraextends beyond Adams County410,053+6.0%Counted whole
Thorntonextends beyond Adams County147,766+3.9%Counted whole
Arvadaextends beyond Adams County122,901−1.2%Counted whole
Westminsterextends beyond Adams County116,182−0.4%Counted whole
Commerce City72,345+15.3%13.0%
Brightonextends beyond Adams County45,395+12.7%Counted whole
Northglennextends beyond Adams County38,893+2.3%Counted whole
Federal Heights14,075−2.2%2.5%
Lochbuieextends beyond Adams County8,776+6.9%Counted whole
Bennettextends beyond Adams County4,224+45.3%Counted whole

10 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 Adams County is counted whole, so it has no share.

Adams County, Homes

Homes in Adams County

Of Adams County's 191,765 homes, 63% are detached houses, against 62% across Colorado; 19% are in buildings of five or more homes. Half of its homes were built before 1990, close to Colorado's 1987: 13% date from before 1960 and 36% from 2000 or later. 69% of occupied homes are lived in by their owner (Colorado: 66%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Adams County, Colorado, 2019 to 2023
HomesAdams CountyColorado
Housing units191,7652,545,124
Detached houses63%62%
In buildings of 5 or more19%22%
Mobile homes6%4%
Built before 196013%16%
Built since 200036%31%
Middle year built19901987
Owner-occupied69%66%

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