Locations and reports
Radon in Rapid City, South Dakota
EPA puts Pennington County, where Rapid City is, in Zone 2, its middle radon zone, and high results are common there: 53.6% of the 1,029 radon tests reported to CDC (2008 to 2017, laboratory totals) came back 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
Share at 4+ pCi/L
53.6%
4.9 pts below SD
- Pennington
- 53.6%
- SD
- 58.5%
Pennington, 18th of 23 in SD, 2008 to 2017
Median result
4.3pCi/L
Action level reached
- Pennington
- 4.3 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of Pennington's tests, 2008 to 2017
Nearest county
65.7%
Custer, 30 miles
- Custer
- 65.7%
- Pennington
- 53.6%
108 tests, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
Pennington, where Rapid City is
Tests reported
1,029
In Pennington
- Pennington
- 1,029
- Custer
- 108
Reported to CDC before any fix, 2008 to 2017
Read a result for Rapid City
Starts at Pennington County's median, 4.3 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.3 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Pennington County's median reported result, 2008 to 2017.
The data
Rapid City, What is published
What is published for Rapid City
Every figure for Rapid City is a county's
Radon data is published by county, not by city, so for Rapid City it is Pennington County's: its EPA zone (Zone 2) and the 1,029 tests reported to CDC for 2008 to 2017, laboratory. Only a test tells you about one home.
Rapid City covers 54.7 square miles of land, all of it in Pennington County. About 80,589 people live there, 1,473 to the square mile.
Rapid City, Counties
The county Rapid City lies in
MeasuredPennington County's EPA zone and the figures CDC publishes for it, 2008 to 2017, laboratory.
Pennington CountyZone 2Moderate predicted potential
- 53.6%
- Reported tests at or above 4 pCi/L
- 4.3 pCi/L
- Median reported result
- 1,029 tests
- Tests reported to CDC
- None
- Yearly figures on file
Pennington County ranks 18th of 23 South Dakota counties with 30 or more tests for that period, 4.9 points below the 58.5% pooled across South Dakota's counties, 17.9 points above the national pool of 35.7%.
The counties nearest Rapid City with a CDC figure for 2008 to 2017, laboratory, measured from the middle of the city: Custer County (30 miles, 65.7% of 108 tests), Lawrence County (35 miles, 56.9% of 160 tests) and Meade County (42 miles, 51.8% of 197 tests). Across the 8 nearest, the share at or above 4 pCi/L runs from 48.8% to 71.0%; the farthest of them, Brown County, is 261 miles away at 71.0%.
No business in the directory gives Rapid City as its address; the South Dakota list covers it. South Dakota's other cities with a page of their own: Sioux Falls and Aberdeen.
The counties around Rapid City
By distance from the middle of Rapid City; counties with 30 or more tests.
Predicted: EPA Map of Radon Zones, by county. Measured: CDC tracking data, by county, 2008 to 2017, laboratory.
Rapid City, Geology
The ground under Rapid City
PredictedUSGS's geologic map splits Rapid City: 58.0% of its land is high radon potential and 42.0% moderate. The map puts 58.0% of Rapid City in the area it calls Black Hills and 37.0% in Black Hills, with one smaller area beside them. USGS gives the first a radon index of 14, in the high band (12 to 17), and the second 11, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Black Hills | Sandstones and shales of Cretaceous age that surround the Black Hills. | High | 14 | 58.0% |
| Black Hills | Late Paleozoic sedimentary or Precambrian intrusive igneous rocks. | Moderate | 11 | 37.0% |
| Pierre Hills | Pierre Shale and Fox Hills sandstone. | Moderate | 10 | 5.0% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Rapid City beside its county and South Dakota
Rapid City sits on more high-potential ground than Pennington County as a whole: 58.0% of the city against 4.0% of the county. On high-potential ground Rapid City is close to South Dakota as a whole: 58.0% of its land against 56.7%.
The map rates the ground, not the air in any home.
Rapid City, Homes
Homes in Rapid City
Of Rapid City's 34,751 homes, 58% are detached houses, against 62% across Pennington County; 23% are in buildings of five or more homes. Half of its homes were built before 1978, close to Pennington County's 1982: 26% date from before 1960 and 26% from 2000 or later. 62% of occupied homes are lived in by their owner (Pennington County: 69%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Rapid City | Pennington County | South Dakota |
|---|---|---|---|
| Housing units | 34,751 | 50,655 | 402,364 |
| Detached houses | 58% | 62% | 67% |
| In buildings of 5 or more | 23% | 17% | 16% |
| Mobile homes | 5% | 10% | 8% |
| Built before 1960 | 26% | 22% | 29% |
| Built since 2000 | 26% | 29% | 28% |
| Middle year built | 1978 | 1982 | 1979 |
| Owner-occupied | 62% | 69% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.
Local help
Rapid City, Local resources
Local resources for Rapid City
Who to ask in South Dakota: its radon program, test kits and professionals.
- South Dakota's radon programDepartment of Agriculture and Natural Resources, phone 1-800-438-3367.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
The Department of Agriculture and Natural Resources (DANR) will provide 500 free Radon test kits to South Dakota Residents.
- Compare kits
- Professionals in South DakotaRadon testers and mitigators in South Dakota, each with how its listing was checked.
The program's own words on licensing are on the South Dakota page.
What it means
Rapid City, Questions
Questions about radon in Rapid City
What radon zone is Rapid City in?
EPA's map puts Pennington County, and with it Rapid City, in Zone 2, the map's middle class: a predicted county average of 2 to 4 pCi/L.
What are radon levels in Rapid City?
53.6% of the 1,029 tests reported from Pennington County for 2008 to 2017 (laboratory totals) were at or above 4 pCi/L, the level at which EPA says to fix a home: high results are ordinary around Rapid City. The median reported result was 4.3 pCi/L.
Should I test my home in Rapid City?
Yes. About 552 of the 1,029 tests reported from Pennington County were at or above 4 pCi/L. That is below South Dakota's pooled 58.5%, and still not a reason to skip it, and ranks Pennington County 18th of the 23 South Dakota counties with 30 or more tests. No map says which homes those are. How to test a home.
What ground is Rapid City built on, as far as radon goes?
58.0% of Rapid City sits on what USGS's map calls "Black Hills", rated high for radon potential, radon index 14; another 37.0% is "Black Hills", rated moderate for radon potential, radon index 11. One smaller area makes up the rest. So the ground changes within Rapid City itself.
Is radon higher in the counties around Rapid City?
Some are and some are not. Against Pennington County's 53.6%, 6 of the 8 nearest counties with a figure report more and 2 less, from Davison County (48.8%, 255 miles off) to Brown County (71.0%, 261 miles off).
The answers use the published figures of Pennington County, the county Rapid City lies in.
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