Is radon high in Thornton, Colorado?

Moderate. Averaging the model's ZIP-code predictions across Thornton (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 2.1 pCi/L - close to the US average of 1.8 and about 20% below the Colorado average of 2.6. That is in the 2-4 pCi/L range where the EPA says to consider fixing. Thornton ranks 17 of 21 Colorado cities on this site.

Which Thornton ZIP codes have the highest radon?

Predictions for the 7 modeled ZIP codes in Thornton range from 1.9 to 2.4 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 86% at or above 2. The city is fairly uniform, so the city-wide number is a reasonable guide for any neighborhood.

Should I test for radon in Thornton?

Yes, soon. With a predicted basement average of 2.1 pCi/L, a meaningful share of Thornton homes will test above the 4 pCi/L action level. Start with a short-term kit; if it reads 2 or higher, confirm with a long-term test or a continuous monitor before paying for mitigation.

What does EPA Radon Zone 1 mean for Thornton?

Thornton sits mainly in Adams County, which the EPA classifies as Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 2.1 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.

Radon levels in Thornton, Colorado

ModerateEPA Zone 1

Predicted long-term basement average of 2.1 pCi/L (model estimate) across the 7 modeled ZIP codes in Thornton - close to the US average of 1.8, about 20% below the Colorado average of 2.6. Ranked #17 of 21 Colorado cities on this site. Most of the city lies in Adams County (its ZIPs also reach into 1 other county).

Test Thornton, CO - the EPA says "consider fixing" in this range

The predicted basement average here is 2.1 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.

Get a short-term test kit →Or track it with a continuous monitor

Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.

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Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.

2.1 ± 0.07

pCi/L predicted basement mean (model SD)

1.8 ± 0.06

pCi/L predicted upstairs (above-ground) mean

1.9-2.4

range of ZIP-level basement predictions in the city

of Thornton ZIPs predicted ≥ 4 pCi/L (86% ≥ 2)

What this means for Thornton

The typical Thornton home is predicted in the 2-4 pCi/L band. The EPA's guidance for this range is to consider fixing, because there is no known safe level and a meaningful minority of homes in a moderate area will test above 4.

The city figure is not a separate estimate: it is the mean of the model's ZIP-code predictions, weighted by the share of the city's land in each ZIP (Census 2020 ZCTA-to-place relationship file). Note that the EPA classifies Adams County as Zone 1 while the newer model predicts 2.1 pCi/L for Thornton; where they disagree, we grade on the model but show both.

Comparable Colorado cities: Denver (2.1), Westminster (2.2), Parker (1.9), Broomfield (2.3).

ZIP codes in Thornton

ZIPs that overlap the city, largest share of its land first. Predicted basement and upstairs means are model estimates; ZIPs the model does not cover show a dash.

ZIP	Share of city	Basement	Upstairs	Grade
80602	35%	2.0 ± 0.06	1.8	Moderate
80229	19%	2.1 ± 0.07	1.9	Moderate
80241	18%	1.9 ± 0.07	1.6	Low
80233	13%	2.1 ± 0.09	1.9	Moderate
80023	7%	2.3 ± 0.06	2.0	Moderate
80260	6%	2.4 ± 0.06	1.9	Moderate
80640	3%	2.1 ± 0.05	1.7	Moderate

Testing help in Colorado

Colorado's radon program page is at cdphe.colorado.gov; it lists testing and certified-mitigator guidance. EPA state radon contacts page. If a test comes back at 4 pCi/L or higher, mitigation typically costs $800-$2,500 installed; use EPA find-a-professional and read the mitigation guide.

Thornton radon questions

Is radon high in Thornton, Colorado?: Moderate. Averaging the model's ZIP-code predictions across Thornton (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 2.1 pCi/L - close to the US average of 1.8 and about 20% below the Colorado average of 2.6. That is in the 2-4 pCi/L range where the EPA says to consider fixing. Thornton ranks 17 of 21 Colorado cities on this site.
Which Thornton ZIP codes have the highest radon?: Predictions for the 7 modeled ZIP codes in Thornton range from 1.9 to 2.4 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 86% at or above 2. The city is fairly uniform, so the city-wide number is a reasonable guide for any neighborhood.
Should I test for radon in Thornton?: Yes, soon. With a predicted basement average of 2.1 pCi/L, a meaningful share of Thornton homes will test above the 4 pCi/L action level. Start with a short-term kit; if it reads 2 or higher, confirm with a long-term test or a continuous monitor before paying for mitigation.
What does EPA Radon Zone 1 mean for Thornton?: Thornton sits mainly in Adams County, which the EPA classifies as Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 2.1 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.

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