Is radon high in Rapid City, South Dakota?

High. Averaging the model's ZIP-code predictions across Rapid City (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 4.8 pCi/L - about 2.7× the US average of 1.8 and about 1.2× the South Dakota average of 3.9. That is at or above the EPA action level of 4 pCi/L. Rapid City ranks 1 of 2 South Dakota cities on this site.

Which Rapid City ZIP codes have the highest radon?

Predictions for the 3 modeled ZIP codes in Rapid City range from 3.9 to 7.1 pCi/L in the basement. 67% of them are predicted at or above 4 pCi/L and 100% at or above 2. That spread is why the ZIP table below matters more than the city-wide number.

Should I test for radon in Rapid City?

Yes, soon. With a predicted basement average of 4.8 pCi/L and ZIPs predicted as high as 7.1, a meaningful share of Rapid City 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 2 mean for Rapid City?

Rapid City sits mainly in Pennington County, which the EPA classifies as Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 4.8 pCi/L does not line up with Zone 2, 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 Rapid City, South Dakota

HighEPA Zone 2

Predicted long-term basement average of 4.8 pCi/L (model estimate) across the 3 modeled ZIP codes in Rapid City - about 2.7× the US average of 1.8, about 1.2× the South Dakota average of 3.9. Ranked #1 of 2 South Dakota cities on this site. Most of the city lies in Pennington County.

Test Rapid City, SD now - and consider a continuous monitor

The model predicts a long-term basement average of 4.8 pCi/L here, at or above the EPA action level of 4. Homes in the same ZIP still vary widely, so a real test is the only way to know your number. A continuous digital monitor shows how your level swings with weather and season, which matters when you're near the action level.

Get a continuous radon monitor →Or start with a short-term test kit

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.

4.8 ± 0.09

pCi/L predicted basement mean (model SD)

2.6 ± 0.07

pCi/L predicted upstairs (above-ground) mean

3.9-7.1

range of ZIP-level basement predictions in the city

67%

of Rapid City ZIPs predicted ≥ 4 pCi/L (100% ≥ 2)

What this means for Rapid City

The typical home in Rapid City is predicted to sit at or above the EPA action level of 4 pCi/L in the basement. A large share of houses here would qualify for mitigation if tested, and buyers routinely ask for radon tests in South Dakota transactions.

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 Pennington County as Zone 2 while the newer model predicts 4.8 pCi/L for Rapid City; where they disagree, we grade on the model but show both.

Comparable South Dakota cities: Sioux Falls (3.0), Cheyenne (2.4), Casper (3.2), Billings (2.9).

ZIP codes in Rapid City

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
57701	42%	4.5 ± 0.10	2.9	High
57702	37%	3.9 ± 0.06	2.1	Moderate
57703	21%	7.1 ± 0.11	3.1	High

Testing help in South Dakota

South Dakota's radon program page is at danr.sd.gov and, when we checked it, offered a limited number of free radon test kits (500 announced). 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.

Rapid City radon questions

Is radon high in Rapid City, South Dakota?: High. Averaging the model's ZIP-code predictions across Rapid City (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 4.8 pCi/L - about 2.7× the US average of 1.8 and about 1.2× the South Dakota average of 3.9. That is at or above the EPA action level of 4 pCi/L. Rapid City ranks 1 of 2 South Dakota cities on this site.
Which Rapid City ZIP codes have the highest radon?: Predictions for the 3 modeled ZIP codes in Rapid City range from 3.9 to 7.1 pCi/L in the basement. 67% of them are predicted at or above 4 pCi/L and 100% at or above 2. That spread is why the ZIP table below matters more than the city-wide number.
Should I test for radon in Rapid City?: Yes, soon. With a predicted basement average of 4.8 pCi/L and ZIPs predicted as high as 7.1, a meaningful share of Rapid City 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 2 mean for Rapid City?: Rapid City sits mainly in Pennington County, which the EPA classifies as Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 4.8 pCi/L does not line up with Zone 2, 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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