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Radon in Aurora, Colorado

Aurora lies in 3 counties, in EPA Zone 1; 60.8% of it is in Arapahoe County, where 37.9% of 1,990 reported tests (2023) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so the only way to know your home's level is to test it.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    37.9%

    1.0 pts below CO

    Arapahoe
    37.9%
    Colorado
    38.9%

    Arapahoe, 23rd of 38 in CO, 2023

  • Median result

    2.5pCi/L

    Below action level

    Arapahoe
    2.5 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of Arapahoe's tests, 2023

  • Highest county

    37.9%

    Arapahoe

    Arapahoe
    37.9%
    Douglas
    35.8%

    3 counties, 3 with 30+ tests, 2023

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    Arapahoe; Adams Zone 1, Douglas Zone 1

  • Tests reported

    1,990

    In Arapahoe

    Arapahoe
    1,990
    Douglas
    1,635

    Reported to CDC before any fix, 2023

Read a result for Aurora

Starts at Arapahoe County's median, 2.5 pCi/L

2.5pCi/L

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

EPA’s reading of 2.5 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. Arapahoe County's median reported result, 2023.

Interpret this readingWhat a fix costs

The data

Aurora, What is published

What is published for Aurora

Information:

Every figure for Aurora is a county's

Radon data is published by county, not by city, and Aurora reaches into 3 counties: Arapahoe County, Adams County and Douglas County. Each has its own EPA zone and its own CDC test figures, set side by side below and each labelled with its county. Only a test tells you about one home.

Aurora covers 160 square miles of land across 3 counties: 60.8% in Arapahoe County, 37.7% in Adams County and 1.5% in Douglas County. About 410,053 people live there, 2,561 to the square mile.

Aurora, Counties

Aurora's counties, side by side

Measured

Each county's own EPA zone and its own published CDC figures for 2023, the newest period any of them has. A county without a figure for that period is shown without one, never with a figure from another year.

  • Arapahoe County
    EPA zone
    Zone 1: Highest predicted potential
    At or above 4 pCi/L
    37.9%
    Median result
    2.5 pCi/L
    Tests reported
    1,990 tests
    Annual years on file
    10
  • Adams County
    EPA zone
    Zone 1: Highest predicted potential
    At or above 4 pCi/L
    36.6%
    Median result
    2.3 pCi/L
    Tests reported
    1,191 tests
    Annual years on file
    10
  • Douglas County
    EPA zone
    Zone 1: Highest predicted potential
    At or above 4 pCi/L
    35.8%
    Median result
    2.4 pCi/L
    Tests reported
    1,635 tests
    Annual years on file
    10
The counties Aurora lies in, each with its own EPA zone and its own published CDC figures for 2023
CountyEPA zoneReported tests at or above 4 pCi/LMedian reported resultTests reportedAnnual years on file
Arapahoe CountyZone 1: Highest predicted potential37.9%2.5 pCi/L1,990 tests10
Adams CountyZone 1: Highest predicted potential36.6%2.3 pCi/L1,191 tests10
Douglas CountyZone 1: Highest predicted potential35.8%2.4 pCi/L1,635 tests10

Aurora spans 3 counties, each with its own EPA zone and its own CDC figure: Arapahoe County (Zone 1, 37.9% of 1,990 tests), Adams County (Zone 1, 36.6% of 1,191 tests) and Douglas County (Zone 1, 35.8% of 1,635 tests).

Arapahoe County ranks 23rd of 38 Colorado counties with 30 or more tests for that period, 1.0 points below the 38.9% pooled across Colorado's counties, 4.5 points above the national pool of 33.4%. Of the city's other counties, Adams County reported 36.6% and Douglas County reported 35.8%.

The counties nearest Aurora with a CDC figure for 2023, measured from the middle of the city: Denver County (9 miles, 35.4% of 2,277 tests), Broomfield County (24 miles, 36.9% of 758 tests) and Jefferson County (29 miles, 41.8% of 3,068 tests). Across the 8 nearest, the share at or above 4 pCi/L runs from 26.4% to 46.0%; the farthest of them, Weld County, is 61 miles away at 46.0%.

No business in the directory gives Aurora as its address; the Colorado list covers it. Colorado's other cities with a page of their own: Colorado Springs, Fort Collins, Grand Junction and Longmont.

Against Colorado and its other counties

Radon test figures for the counties Aurora lies in
CountyShare of AuroraTestsAt or above 4 pCi/LMedianColorado, pooledRank in the stateEPA zone
Arapahoe County60.8%1,99037.9%2.5 pCi/L38.9%23 of 38Zone 1
Adams County37.7%1,19136.6%2.3 pCi/L38.9%26 of 38Zone 1
Douglas County1.5%1,63535.8%2.4 pCi/L38.9%28 of 38Zone 1

Shares of tests people chose to run and report, by county (2023); the state's is its counties' counts added up, calculated by Radon411. Only a test measures a home.

The counties around Aurora

By distance from the middle of Aurora; counties with 30 or more tests.

Nearest counties to Aurora with 30 or more tests
CountyDistanceTestsAt or above 4 pCi/LMedian
Denver County9 mi2,27735.4%2.8 pCi/L
Broomfield County24 mi75836.9%2.3 pCi/L
Jefferson County29 mi3,06841.8%3.2 pCi/L
Elbert County43 mi12045.8%2.9 pCi/L
Boulder County43 mi1,96334.2%2.5 pCi/L
Gilpin County44 mi12926.4%1.1 pCi/L
Clear Creek County49 mi5141.2%3.0 pCi/L
Weld County61 mi66346.0%3.5 pCi/L

The median reported pre-mitigation result for 2023 was 2.5 pCi/L in Arapahoe County, 2.3 pCi/L in Adams County and 2.4 pCi/L in Douglas County.

Predicted: EPA Map of Radon Zones, by county. Measured: CDC tracking data, by county, 2023.

Aurora, Geology

The ground under Aurora

Predicted

USGS's geologic map puts all of Aurora's mapped land in one class: high radon potential. The map puts 72.5% of Aurora in the area it calls Dawson Arkose and 27.5% in High Plains. USGS gives the first a radon index of 14 and the second 12, both in the high band (12 to 17).

USGS's geologic areas under Aurora
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Dawson ArkoseConsolidated alluvial fan and river deposits sourced in the granite mountains to the west.High1472.5%
High PlainsQuaternary deposits and Cretaceous marine shales that locally have a high radiometric signature.High1227.5%

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

Aurora beside its counties and Colorado

All of Aurora, like all of Arapahoe County, is rated high. Aurora has more high-potential ground than Colorado as a whole: 100% of its land against 74.8%.

Share of land by USGS radon potential: Aurora, the counties it lies in and Colorado
AreaEPA zoneLow potentialModerate potentialHigh potential
AuroraBy countyNoneNone100%
Arapahoe CountyZone 1NoneNone100%
Adams CountyZone 1NoneNone100%
Douglas CountyZone 1NoneNone100%
Colorado64 counties, pooled by land areaVariesNone25.2%74.8%

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

Aurora, Homes

Homes in Aurora

Fewer than six in ten of Aurora's 150,242 homes are detached houses (53%, against 56% across Arapahoe County); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1985, close to Arapahoe County's 1985: 8% date from before 1960 and 28% from 2000 or later. 63% of occupied homes are lived in by their owner (Arapahoe County: 65%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Aurora, Arapahoe County, Colorado, 2019 to 2023
HomesAuroraArapahoe CountyColorado
Housing units150,242265,9802,545,124
Detached houses53%56%62%
In buildings of 5 or more29%29%22%
Mobile homes2%1%4%
Built before 19608%9%16%
Built since 200028%26%31%
Middle year built198519851987
Owner-occupied63%65%66%

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

Local help

Aurora, Local resources

Local resources for Aurora

Who to ask in Colorado: its radon program, test kits and professionals.

The program's own words on licensing and disclosure are on the Colorado page.

What it means

Aurora, Questions

Questions about radon in Aurora

What radon zone is Aurora in?

All 3 counties Aurora reaches into (Arapahoe County, Adams County and Douglas County) are in Zone 1, the map's highest class: a predicted county average above 4 pCi/L. EPA zones counties, not cities, so that is the zone for every part of Aurora.

What are radon levels in Aurora?

A high result is no surprise around Aurora: 37.9% of 1,990 tests reported from Arapahoe County for 2023 reached 4 pCi/L or more. The median reported result was 2.5 pCi/L. Adams County reported 36.6% of 1,191 tests and Douglas County reported 35.8% of 1,635 tests; the counties are kept apart.

Should I test my home in Aurora?

Yes. About 754 of the 1,990 tests reported from Arapahoe County were at or above 4 pCi/L. That is about what Colorado as a whole reports (38.9%), and ranks Arapahoe County 23rd of the 38 Colorado counties with 30 or more tests. No map says which homes those are. How to test a home.

What ground is Aurora built on, as far as radon goes?

72.5% of Aurora sits on what USGS's map calls "Dawson Arkose", rated high for radon potential, radon index 14; another 27.5% is "High Plains", in the same class.

Is radon higher in the counties around Aurora?

Some are and some are not. Against Arapahoe County's 37.9%, 4 of the 8 nearest counties with a figure report more and 4 less, from Gilpin County (26.4%, 44 miles off) to Weld County (46.0%, 61 miles off).

The answers use the published figures of Arapahoe County, Adams County and Douglas County, the counties Aurora lies in.

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