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Radon in Boulder, Montana

EPA puts Jefferson County, where Boulder is, in Zone 1, its highest radon zone, and high results are common there: 71.0% of the 62 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    71.0%

    25.5 pts above MT

    Jefferson
    71.0%
    Montana
    45.5%

    Jefferson, 4th of 23 in MT, 2008 to 2017

  • Median result

    6.3pCi/L

    Action level reached

    Jefferson
    6.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of Jefferson's tests, 2008 to 2017

  • Nearest county

    70.1%

    Silver Bow, 35 miles

    Silver Bow
    70.1%
    Jefferson
    71.0%

    174 tests, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    Jefferson, where Boulder is

  • Tests reported

    62

    In Jefferson

    Jefferson
    62
    Silver Bow
    174

    Reported to CDC before any fix, 2008 to 2017

Read a result for Boulder

Starts at Jefferson County's median, 6.3 pCi/L

6.3pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 6.3 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. Jefferson County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Boulder, What is published

What is published for Boulder

Information:

Every figure for Boulder is a county's

Radon data is published by county, not by city, so for Boulder it is Jefferson County's: its EPA zone (Zone 1) and the 62 tests reported to CDC for 2008 to 2017, laboratory. Only a test tells you about one home.

Boulder covers 1.1 square miles of land, all of it in Jefferson County. About 1,305 people live there, 1,161 to the square mile.

Boulder, Counties

The county Boulder lies in

Measured

Jefferson County's EPA zone and the figures CDC publishes for it, 2008 to 2017, laboratory.

Jefferson CountyZone 1Highest predicted potential

71.0%
Reported tests at or above 4 pCi/L
6.3 pCi/L
Median reported result
62 tests
Tests reported to CDC
None
Yearly figures on file

Jefferson County ranks 4th of 23 Montana counties with 30 or more tests for that period, 25.5 points above the 45.5% pooled across Montana's counties, 35.3 points above the national pool of 35.7%.

Measured from the middle of Boulder, the nearest counties with a CDC figure for 2008 to 2017, laboratory are Silver Bow County (35 miles, 70.1% of 174 tests), Lewis and Clark County (63 miles, 61.8% of 468 tests) and Madison County (65 miles, 50.0% of 58 tests). Across the 8 nearest, the share at or above 4 pCi/L runs from 29.4% to 70.1%; the farthest of them, Ravalli County, is 97 miles away at 44.6%.

No business in the directory gives Boulder as its address; the Montana list covers it. Montana's other cities with a page of their own: Bozeman, Kalispell, Billings and Helena.

The counties around Boulder

By distance from the middle of Boulder; counties with 30 or more tests.

Nearest counties to Boulder with 30 or more tests
CountyDistanceTestsAt or above 4 pCi/LMedian
Silver Bow County35 mi17470.1%6.0 pCi/L
Lewis and Clark County63 mi46861.8%5.1 pCi/L
Madison County65 mi5850.0%3.9 pCi/L
Gallatin County66 mi1,60042.8%3.2 pCi/L
Cascade County83 mi23529.4%1.7 pCi/L
Beaverhead County85 mi3759.5%5.0 pCi/L
Park County93 mi15060.0%5.3 pCi/L
Ravalli County97 mi1,09044.6%3.5 pCi/L

Predicted: EPA Map of Radon Zones, by county. Measured: CDC tracking data, by county, 2008 to 2017, laboratory.

Boulder, Geology

The ground under Boulder

Predicted

USGS's geologic map puts all of Boulder'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 Boulder
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northern Rocky MountainsGranitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium.High13100%

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

Boulder beside its county and Montana

All of Boulder, like all of Jefferson County, is rated high. Boulder has more high-potential ground than Montana as a whole: 100% of its land against 78.5%.

Share of land by USGS radon potential: Boulder, the county it lies in and Montana
AreaEPA zoneLow potentialModerate potentialHigh potential
BoulderBy countyNoneNone100%
Jefferson CountyZone 1NoneNone100%
Montana56 counties, pooled by land areaVariesNone21.5%78.5%

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

Boulder, Homes

Homes in Boulder

Of Boulder's 585 homes, 75% are detached houses, against 84% across Jefferson County; 20% are mobile homes. The homes are older than Jefferson County's as a whole: half were built before 1972 (1989 for Jefferson County), and 36% date from before 1960. 71% of occupied homes are lived in by their owner (Jefferson County: 83%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Boulder, Jefferson County, Montana, 2019 to 2023
HomesBoulderJefferson CountyMontana
Housing units5855,388522,939
Detached houses75%84%69%
In buildings of 5 or more5%2%9%
Mobile homes20%10%10%
Built before 196036%18%26%
Built since 200022%30%27%
Middle year built197219891980
Owner-occupied71%83%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

Boulder, Local resources

Local resources for Boulder

Who to ask in Montana: its radon program, test kits and professionals.

The program's own words on licensing are on the Montana page.

What it means

Boulder, Questions

Questions about radon in Boulder

What radon zone is Boulder in?

EPA's map puts Jefferson County, and with it Boulder, in Zone 1, the map's highest class: a predicted county average above 4 pCi/L.

What are radon levels in Boulder?

High results are ordinary around Boulder: 71.0% of the 62 tests reported from Jefferson County for 2008 to 2017 (laboratory totals) were at or above 4 pCi/L, the level at which EPA says to fix a home. The median reported result was 6.3 pCi/L.

Should I test my home in Boulder?

Yes. Jefferson County reported about 44 of its 62 tests at or above 4 pCi/L. That is above Montana's pooled 45.5%, and ranks Jefferson County 4th of the 23 Montana counties with 30 or more tests. Which homes they were, no map can say. How to test a home.

What ground is Boulder built on, as far as radon goes?

USGS's geologic map puts all of Boulder on one named area, "Northern Rocky Mountains", rated high for radon potential, radon index 13.

Is radon higher in the counties around Boulder?

Lower: none of the 8 nearest counties with a figure matches Jefferson County's 71.0%. The closest to it is Silver Bow County (70.1%, 35 miles off); the lowest is Cascade County (29.4%, 83 miles off).

The answers use the published figures of Jefferson County, the county Boulder lies in.

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