Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Slope County, North Dakota
EPA puts Slope County in Zone 1, its highest radon zone, and only 10 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
71.4%
Bowman County
- Bowman
- 71.4%
- Stark
- 62.4%
2 of 7 neighbours have 30+ tests, 2008 to 2017
Nearest county
71.4%
Bowman County, 23 miles
- Bowman
- 71.4%
- ND
- 59.3%
Share at 4+ pCi/L, 35 tests, 2008 to 2017
Ground above low
100.0%
Level with ND
- Slope
- 100.0%
- ND
- 100.0%
Share of land USGS rates moderate or high potential
Tests reported
17
Too few for a share
- Slope
- 17
- Needed
- 30
2005 to 2014, laboratory
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Read a result for Slope County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 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.
The data
Slope County, At a glance
Slope County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Slope County in
USGS geologic potential: High across 91% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Slope County, 2008 to 2017, laboratory
CDC holds 10 reported tests for Slope County over the 2008 to 2017 laboratory totals, with a median of 10.3 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Slope County beside the counties around it is how this page reads it.
What these figures count
Only 10 tests were reported to CDC for Slope County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Slope County, Compared
Slope County radon figures, compared
Calculated by Radon411CDC's largest figure for Slope County rests on 17 tests over the 2005 to 2014 laboratory totals, 13 of them at or above 4 pCi/L, so each test moves its share by 5.9 points and no rank or comparison is drawn from it. Results reached as high as 26.8 pCi/L, with a middle value of 16.0 pCi/L.
Of the counties bordering it, 2 have a figure over the 2008 to 2017 laboratory totals: Bowman County reported the largest share at or above 4 pCi/L, 71.4%, and Stark County the smallest, 62.4%. Farther out, Dunn County (74 miles away) at 74.3%, McKenzie County (89 miles away) at 56.1% and Mercer County (97 miles away) at 63.5% have figures too. Pooled across 53 North Dakota counties, 59.3% of reported tests reached that level; across every county in the country with a figure, 35.7%.
Statewide for the same period, Pembina County reported the highest share (82.5%) and Williams County the lowest (33.8%). EPA's 1993 map puts Slope County in Zone 1, the map's highest label: a predicted county average above 4 pCi/L. USGS geology rates 91% of the county's land high radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Slope County, Geology
The ground under Slope County
PredictedMost of the ground under Slope County is one class on USGS's geologic map: 90.5% of its land is high radon potential, with 9.5% moderate. The map puts 90.5% of Slope County in the area it calls Great Plains (Unglaciated) and 9.5% in Eastern Great Plains. USGS gives the first a radon index of 13, 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 |
|---|---|---|---|---|
| Great Plains (Unglaciated) | Tertiary and Upper Cretaceous sandstones, shales, and locally, coal-bearing units. | High | 13 | 90.5% |
| Eastern Great Plains | Cretaceous marine shale and marine and nearshore sandstone, siltstone. | Moderate | 11 | 9.5% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Slope County beside the ground around it
On high-potential ground Slope County is close to North Dakota as a whole: 90.5% of its land against 98.9%. Of the 7 counties that border it, 5 have more high-potential ground, Adams County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Slope County, Local resources
Radon testing and mitigation in Slope County
- North Dakota's radon programNorth Dakota Department of Environmental QualityNorth Dakota's radon program offers free or discounted test kits, and answers questions about testing and mitigation in North Dakota.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Notice: The DEQ is out of free radon test kits.
- Compare kits
- Professionals in North Dakota47 professionals are listed in North Dakota.
What North Dakota's program says
- Phone
- 701-328-5166
- jOtto@nd.gov
What it means
Slope County, Questions
Questions about radon in Slope County
Are radon levels high in Slope County?
Over the 2008 to 2017 laboratory totals, 70.0% of the radon tests reported to CDC for Slope County, North Dakota were at or above 4 pCi/L, and the median reported pre-mitigation result was 10.3 pCi/L. Of the counties bordering it, 2 have a figure over the 2008 to 2017 laboratory totals: Bowman County reported the largest share at or above 4 pCi/L, 71.4%, and Stark County the smallest, 62.4%.
Which counties border Slope County?
Slope County borders 7 counties: Bowman County, ND, Billings County, ND, Golden Valley County, ND, Fallon County, MT, Hettinger County, ND, Stark County, ND and Adams County, ND.
Products
Slope County, Products
Testing a home in Slope County
No CDC figure names Slope County; the nearest county with one, Bowman County (23 miles away), reported 71.4% of its tests at or above 4 pCi/L over the 2008 to 2017 laboratory totals, the only reading nearby until a test of this home. In Zone 1 the year-round level in Slope County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
MonitorAEGTEST
HOUND-3786 rechargeable radon monitor with a 3.5-inch color screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Ion chamber
First reading: Within 10 minutes
Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Slope County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Slope County
Explore
Slope County, Bordering counties
Counties bordering Slope County
Calculated by Radon411- Radon levels in Billings County, NDEPA zone 1
85.0%at or above 4 pCi/L
Median 11.0 pCi/L · 20 tests
- Radon levels in Adams County, NDEPA zone 1
80.0%at or above 4 pCi/L
Median 12.7 pCi/L · 10 tests
- Radon levels in Bowman County, NDEPA zone 1
71.4%at or above 4 pCi/L
Median 5.8 pCi/L · 35 tests
- Radon levels in Golden Valley County, NDEPA zone 1
71.4%at or above 4 pCi/L
Median 6.2 pCi/L · 7 tests
- Radon levels in Fallon County, MTEPA zone 1
62.5%at or above 4 pCi/L
Median 4.7 pCi/L · 8 tests
- Radon levels in Hettinger County, NDEPA zone 1
62.5%at or above 4 pCi/L
Median 5.8 pCi/L · 16 tests
- Radon levels in Stark County, NDEPA zone 1
62.4%at or above 4 pCi/L
Median 5.1 pCi/L · 386 tests
Slope County, Cities and towns
Cities and towns in Slope County
Slope County has been losing residents: from 697 in 2020 to 628 on July 1, 2025, a fall of 9.9% by the Census Bureau's estimates. Spread over its land, that is 0.5 people to the square mile. No town dominates: Marmarth, the largest, has 91 residents, 14.5% of the total. Together its 2 incorporated places hold 17.8% of those residents; the other 82.2% live outside any of them. Testing is reported here more often than across the state: CDC's 17 reported tests for 2005 to 2014 come to 27.1 for every 1,000 residents (2025 estimate), against 8.2 for North Dakota.
From Marmarth to Amidon, CDC publishes no figure by town: each reads Slope County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Marmarth | 91 | −9.9% | 14.5% |
| Amidon | 21 | −12.5% | 3.3% |
2 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Slope County, Homes
Homes in Slope County
Slope County is a place of houses on their own lots: 87% of its 458 homes are detached single-family houses, against 57% across North Dakota. The homes are older than North Dakota's as a whole: half were built before 1954 (1981 for North Dakota), and 58% date from before 1960. Owners live in 87% of the occupied homes (North Dakota: 63%), so for most households a test and a fix are their own to order.
| Homes | Slope County | North Dakota |
|---|---|---|
| Housing units | 458 | 374,866 |
| Detached houses | 87% | 57% |
| In buildings of 5 or more | under 1% | 25% |
| Mobile homes | 11% | 7% |
| Built before 1960 | 58% | 24% |
| Built since 2000 | 14% | 31% |
| Middle year built | 1954 | 1981 |
| Owner-occupied | 87% | 63% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.