Is radon high in Columbia, Maryland?

Low. Averaging the model's ZIP-code predictions across Columbia (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.1 pCi/L - about 37% below the US average of 1.8 and close to the Maryland average of 1.3. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Columbia ranks 10 of 20 Maryland cities on this site.

Which Columbia ZIP codes have the highest radon?

Predictions for the 5 modeled ZIP codes in Columbia range from 1.0 to 1.4 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 0% 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 Columbia?

Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; Columbia's low predicted average describes the typical home, not yours.

What does EPA Radon Zone 1 mean for Columbia?

Columbia sits mainly in Howard 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 1.1 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 Columbia, Maryland

LowEPA Zone 1

Predicted long-term basement average of 1.1 pCi/L (model estimate) across the 5 modeled ZIP codes in Columbia - about 37% below the US average of 1.8, close to the Maryland average of 1.3. Ranked #10 of 20 Maryland cities on this site. Most of the census-designated place lies in Howard County.

Test Columbia, MD once anyway - radon varies house to house

The predicted basement average here is 1.1 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.

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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.

1.1 ± 0.11

pCi/L predicted basement mean (model SD)

1.0 ± 0.09

pCi/L predicted upstairs (above-ground) mean

1.0-1.4

range of ZIP-level basement predictions in the city

of Columbia ZIPs predicted ≥ 4 pCi/L (0% ≥ 2)

What this means for Columbia

The typical Columbia home is predicted below 2 pCi/L, the lowest band. That describes the average house; the ZIP-level predictions inside the city still span 1.0 to 1.4 pCi/L.

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 census-designated place's land in each ZIP (Census 2020 ZCTA-to-place relationship file). Note that the EPA classifies Howard County as Zone 1 while the newer model predicts 1.1 pCi/L for Columbia; where they disagree, we grade on the model but show both.

Comparable Maryland cities: Bethesda (1.1), Frederick (1.1), Wheaton (1.2), Bel Air South (1.1).

ZIP codes in Columbia

ZIPs that overlap the census-designated place, 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
21044	35%	1.2 ± 0.12	1.1	Low
21045	30%	1.0 ± 0.09	0.9	Low
21046	25%	1.2 ± 0.11	1.0	Low
21029	9%	1.4 ± 0.10	1.2	Low
21075	1%	1.1 ± 0.06	0.7	Low

Testing help in Maryland

Maryland's radon program page is at mde.maryland.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.

Columbia radon questions

Is radon high in Columbia, Maryland?: Low. Averaging the model's ZIP-code predictions across Columbia (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.1 pCi/L - about 37% below the US average of 1.8 and close to the Maryland average of 1.3. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Columbia ranks 10 of 20 Maryland cities on this site.
Which Columbia ZIP codes have the highest radon?: Predictions for the 5 modeled ZIP codes in Columbia range from 1.0 to 1.4 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 0% 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 Columbia?: Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; Columbia's low predicted average describes the typical home, not yours.
What does EPA Radon Zone 1 mean for Columbia?: Columbia sits mainly in Howard 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 1.1 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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