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Radon Levels in Sanders County, Montana

EPA puts Sanders County in Zone 1, its highest radon zone, and high results are common there: 50.0% of the 38 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

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  • Share at 4+ pCi/L

    50.0%

    4.5 pts above MT

    Sanders
    50.0%
    Montana
    45.5%

    38 tests, 2008 to 2017

  • Median result

    4.0pCi/L

    Action level reached

    Sanders
    4.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    38

    21st of 23 by tests

    Sanders
    38
    Missoula
    2,613

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Montana

    14 of 23

    Middle half

    Sanders
    50.0%
    Richland
    78.6%

    By share, of 23 with 30+ tests

Read a result for Sanders County

Starts at Sanders County's median, 4.0 pCi/L

4.0pCi/L

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

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 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. Sanders County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Sanders County, At a glance

Sanders County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Sanders County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Sanders County, 2008 to 2017, laboratory

Reported results by concentration band, Sanders County, 2008 to 2017, laboratory
Under 2 pCi/L: 34%2 to 4 pCi/L: 16%4 pCi/L and above: 50%

Of 38 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Sanders County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1334.2%
2 to 4 pCi/L615.8%
4 pCi/L and above1950.0%
What these figures count

These are the 38 tests reported to CDC for Sanders County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Sanders County, Compared

Sanders County radon figures, compared

Calculated by Radon411

More than half: 50.0% of the 38 radon tests reported to CDC for Sanders County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 14th of 23 Montana counties with 30 or more tests for the same period. That is 4.5 points above the 45.5% pooled from 51 Montana counties.

The median result, 4.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 65.5 pCi/L. The rest split 34.2% under 2 pCi/L and 15.8% from 2 to 4 (Montana: 29.2% and 25.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 50.0% share point the same way here.

3 of its 7 bordering counties with figures ran higher, led by Shoshone County, ID at 63.0%; Bonner County, ID reported 33.0%. Statewide for the same period, Richland County reported the highest share (78.6%) and Cascade County the lowest (29.4%).

CDC's ten-year totals for Sanders County went from 39 tests (2005 to 2014) to 38 (2008 to 2017), the share going from 56.4% to 50.0%.

Nationally, every county with a figure for the same period pools to 35.7%; Sanders County sits 14.3 points above it.

Sanders County against Montana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Sanders County
Sanders County3850.0%4.0 pCi/LThis county
Montana, pooled51 counties, pooled9,89345.5%Not pooled−4.5 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−14.3 points
Richland Countyhighest in the state4278.6%5.9 pCi/L+28.6 points
Cascade Countylowest in the state23529.4%1.7 pCi/L−20.6 points
Shoshone County, IDborders it8163.0%5.7 pCi/L+13.0 points
Mineral County, MTborders it3056.7%5.1 pCi/L+6.7 points
Lincoln County, MTborders it7451.4%4.0 pCi/L+1.4 points
Missoula County, MTborders it2,61344.6%3.4 pCi/L−5.4 points
Lake County, MTborders it14940.3%2.9 pCi/L−9.7 points
Flathead County, MTborders it89137.8%3.0 pCi/L−12.2 points
Bonner County, IDborders it32133.0%2.3 pCi/L−17.0 points
Where Sanders County's reported results fell, 2008 to 2017, laboratory, beside Montana and the United States
ResultSanders County testsSanders County shareMontana shareU.S. shareAgainst Montana
Under 2 pCi/L1334.2%29.2%39.6%+5.0 points
2 to 4 pCi/L615.8%25.2%24.7%−9.4 points
4 pCi/L and above1950.0%45.5%35.7%+4.5 points
Sanders County ranked among the 23 Montana counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Mineral County10 of 233056.7%5.1 pCi/L
Stillwater County11 of 235955.9%4.8 pCi/L
Carbon County12 of 234652.2%4.2 pCi/L
Lincoln County13 of 237451.4%4.0 pCi/L
Madison County14 of 235850.0%3.9 pCi/L
Sanders County14 of 233850.0%4.0 pCi/L
Dawson County16 of 235947.5%3.5 pCi/L
Missoula County17 of 232,61344.6%3.4 pCi/L
Ravalli County18 of 231,09044.6%3.5 pCi/L
Gallatin County19 of 231,60042.8%3.2 pCi/L
Yellowstone County20 of 231,52042.4%3.4 pCi/L
Sanders County ten-year laboratory totals, against Montana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMontana, pooledChange from the row before
2008 to 20173850.0%4.0 pCi/L65.5 pCi/L45.5%−2.5 points
2007 to 20164052.5%4.2 pCi/L65.5 pCi/L46.6%−1.0 points
2006 to 20154353.5%4.2 pCi/L65.5 pCi/L47.4%−2.9 points
2005 to 20143956.4%5.3 pCi/L65.5 pCi/L48.0%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Sanders County, Geology

The ground under Sanders County

Predicted

USGS's geologic map puts all of Sanders County's mapped land in one class: high radon potential. All of it lies in the area the map calls Northern Rocky Mountains, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Sanders County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northern Rocky MountainsGranitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium.High1399.9%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Sanders County beside the ground around it

Sanders County has more high-potential ground than Montana as a whole: 100% of its land against 78.5%. Of the 7 counties that border it, none has as large a share of high-potential ground; Flathead County comes nearest at 100%.

Share of land by USGS radon potential: Sanders County, the 7 counties bordering it and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
Sanders CountyZone 1NoneNone100%
Mineral CountyZone 1NoneNone100%
Shoshone County, IDZone 1NoneNone100%
Lake CountyZone 1NoneNone100%
Lincoln CountyZone 1NoneNone100%
Flathead CountyZone 1NoneNone100%
Missoula CountyZone 1NoneNone100%
Bonner County, IDZone 1NoneNone100%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

The map rates the ground, not the air in any home.

Local help

Sanders County, Local resources

Radon testing and mitigation in Sanders County

What Montana's program says
Phone
1-800-546-0483
Licensing of radon professionals
Montana DEQ does not certify or require proof of certification for the contractors listed.

What it means

Sanders County, Questions

Questions about radon in Sanders County

Are radon levels high in Sanders County?

Over the 2008 to 2017 laboratory totals, 50.0% of the radon tests reported to CDC for Sanders County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.0 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 13 reported a higher share; pooled, the state comes to 45.5%.

Which counties border Sanders County?

Sanders County borders 7 counties: Mineral County, MT, Shoshone County, ID, Lake County, MT, Lincoln County, MT, Flathead County, MT, Missoula County, MT and Bonner County, ID.

Products

Sanders County, Products

Testing a home in Sanders County

In Sanders County, 50.0% of 38 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 45.5% pooled across Montana. In Zone 1 the year-round level in Sanders 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

Sanders County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Sanders County

Explore

Sanders County, Bordering counties

Counties bordering Sanders County

Calculated by Radon411

Sanders County, Cities and towns

Cities and towns in Sanders County

Sanders County is growing: the Census Bureau puts it at 14,062 residents on July 1, 2025, up 12.9% from 12,454 in 2020. Spread over its land, that is 5.1 people to the square mile. No town dominates: Thompson Falls, the largest, has 1,543 residents, 11.0% of the total. Together its 3 incorporated places hold 24.4% of those residents; the other 75.6% live outside any of them. Reported testing is thin here: 38 tests over 2008 to 2017, or 2.7 for every 1,000 residents (2025 estimate), where Montana as a whole comes to 8.6.

From Thompson Falls to Hot Springs, CDC publishes no figure by town: each reads Sanders County's.

The cities and towns in Sanders County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Thompson Falls1,543+13.0%11.0%
Plains1,261+13.1%9.0%
Hot Springs630+11.9%4.5%

3 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).

Sanders County, Homes

Homes in Sanders County

Sanders County is a place of houses on their own lots: 80% of its 6,789 homes are detached single-family houses, against 69% across Montana. Much of Sanders County is recent building: 33% of its homes have gone up since 2000 and the middle year built is 1989, against 1980 for Montana. Owners live in 80% of the occupied homes (Montana: 69%), so for most households a test and a fix are their own to order.

Homes in Sanders County, Montana, 2019 to 2023
HomesSanders CountyMontana
Housing units6,789522,939
Detached houses80%69%
In buildings of 5 or more2%9%
Mobile homes15%10%
Built before 196021%26%
Built since 200033%27%
Middle year built19891980
Owner-occupied80%69%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.