Radon in Clark County, South Dakota
Clark County, South Dakota, is in EPA radon Zone 1: predicted average indoor radon screening level greater than 4 pCi/L (highest potential). Radon laboratories reported 6 building tests here for 2008 to 2017: median 5.9 pCi/L, with 77.8% at or above EPA's 4 pCi/L action level (South Dakota 58.6%, US 36.5%).
Radon test results in Clark County
| Test results | Period | Tests | Typical result | 4 pCi/L or more |
|---|---|---|---|---|
| Radon testing laboratories | 2008-2017 | 6 | median 5.9 pCi/L | 77.8% |
| South Dakota, all counties (labs) | 2008-2017 | 4,760 | n/a | 58.6% |
| United States (labs) | 2008-2017 | 1,408,802 | n/a | 36.5% |
Test results describe buildings whose owners chose to test and whose results reached the lab or agency, not a random sample; small counts swing widely. State and US shares are computed from county counts and percents. The laboratory data comes from national radon testing laboratories and supplements EPA's zone map.
Radon in nearby counties
| County | EPA zone | Lab tests | 4 pCi/L or more |
|---|---|---|---|
| Codington County, SD | Zone 1 | 58 | 64.9% |
| Hamlin County, SD | Zone 1 | 11 | 76.9% |
| Spink County, SD | Zone 1 | 15 | 50% |
| Day County, SD | Zone 1 | 8 | 54.5% |
| Kingsbury County, SD | Zone 1 | 27 | 68.2% |
| Beadle County, SD | Zone 1 | 40 | 59.3% |
The six counties with the nearest centers.
What to do about radon in Clark County
Test the building. EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, and says there is no known safe level of exposure. South Dakota's state radon program can point you to testers and test kits.
Buying here? The Environmental Records Report lists this county's radon zone and test results with the flood zone, mapped faults, power lines and federal contamination records near the address.
Radon in Clark County: questions
What is the radon level in Clark County?
The median of the 6 laboratory tests reported for Clark County (2008 to 2017) was 5.9 pCi/L, and 77.8% of them were at or above 4 pCi/L. These are results of tested buildings; a single home can be far above or below them.
Is Clark County in radon Zone 1?
Yes. EPA's 1993 Map of Radon Zones puts Clark County in Zone 1, the counties with a predicted average indoor radon screening level above 4 pCi/L.
How does radon in Clark County compare with South Dakota?
77.8% of laboratory tests in Clark County were at or above 4 pCi/L for 2008 to 2017, against 58.6% across South Dakota (4,760 tests) and 36.5% nationally. 48 of South Dakota's 66 counties are in Zone 1.
Should I test for radon in Clark County?
Yes. EPA recommends testing every home whatever its zone: "This map should not be used to determine if individual homes need to be tested." Fix the home at 4 pCi/L or more and consider a fix between 2 and 4 pCi/L; EPA says there is no known safe level of radon exposure.
More for Clark County
- Clark loan limitsThis year's FHFA conforming, FHA and VA county loan limits for 1 to 4 unit homes, from FHFA's and HUD's official files.
- Clark fair market rentHUD Fair Market Rents for studios to 4 bedrooms, the voucher payment standard range and the change from last year.
- Clark property tax rateEffective property tax rate from Census survey data: median taxes paid against median home value, ranked in the state.
- Environmental records reportSuperfund, hazardous waste, leaking tank and brownfield sites near any Clark address, with distances and a site map. A records search, not a Phase I.
- Superfund sites in South DakotaEvery EPA Superfund site in South Dakota with its status, county and a map, refreshed nightly from federal records.
- USDA eligibility map: South DakotaHow much of each South Dakota county is in a USDA-eligible rural area, the towns mapped ineligible, and a free address check.
- Opportunity zones in South DakotaEvery designated Opportunity Zone tract in South Dakota by county, from the IRS list, and the tracts eligible for the 2027 round.
- Census tract lookupThe census tract of any Clark address with its FFIEC income level and HUD Qualified Census Tract and DDA status.
Other free hazard lookups
- Fault lines near an addressUSGS-mapped earthquake faults within 5 miles, their age and slip rate, and the USGS seismic hazard value.
- Power lines near an addressHigh-voltage transmission lines within 1 mile from federal maps, with voltage and distance.
- Flood zone lookupThe FEMA flood zone mapped at any US address. Not an official flood zone determination.
- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Radon in every South Dakota county · Radon map of every state
Data compiled 2026-10-20. County FIPS 46025. County-level screening information, not a radon measurement of any building.