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Radon Levels in Gem County, Idaho

EPA puts Gem County in Zone 3, its lowest radon zone, and 20.2% of its 99 reported radon tests (2008 to 2017, laboratory totals) were 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

    20.2%

    21.3 pts below ID

    Gem
    20.2%
    Idaho
    41.5%

    99 tests, 2008 to 2017

  • Median result

    1.9pCi/L

    Below action level

    Gem
    1.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    99

    20th of 37 by tests

    Gem
    99
    Ada
    3,030

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 3

    Lower potential

    1. 1
    2. 2
    3. Zone 3

    1 highest, 3 lowest

    EPA predicts under 2 pCi/L indoors

  • Rank in Idaho

    32 of 37

    Lowest quarter

    Gem
    20.2%
    Bear Lake
    78.1%

    By share, of 37 with 30+ tests

Read a result for Gem County

Starts at Gem County's median, 1.9 pCi/L

1.9pCi/L

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

EPA’s reading of 1.9 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. Gem County's median reported result, 2008 to 2017.

Interpret this reading

The data

Gem County, At a glance

Gem County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Gem County as a whole is an average indoor of less than 2 pCi/L (less than 75 Bq/m³). A low zone clears no address in it: homes above EPA's turn up in all three zones.

USGS geologic potential: Low across 49% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Gem County, 2008 to 2017, laboratory
Under 2 pCi/L: 55%2 to 4 pCi/L: 25%4 pCi/L and above: 20%

Of 99 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Gem County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L5454.5%
2 to 4 pCi/L2525.3%
4 pCi/L and above2020.2%
What these figures count

These are the 99 tests reported to CDC for Gem 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

Gem County, Compared

Gem County radon figures, compared

Calculated by Radon411

Gem County's 99 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.9 pCi/L and a maximum of 14.5 pCi/L, and 20.2% reached 4 pCi/L. Idaho as a whole (44 Idaho counties, pooled) comes to 41.5%: 21.3 points higher than here.

Among its state's counties it ranks 32nd of 37 Idaho counties with 30 or more tests for the same period. Statewide for the same period, Bear Lake County reported the highest share (78.1%) and Payette County the lowest (4.9%).

Below the action level, 54 tests (54.5%) came in under 2 pCi/L, against 31.5% statewide, and 25 tests (25.3%) fell between 2 and 4, against 26.9% statewide. CDC's ten-year totals for Gem County went from 75 tests (2005 to 2014) to 99 (2008 to 2017), the share going from 17.3% to 20.2%.

EPA's 1993 zone map puts Gem County in Zone 3, a predicted county average under 2 pCi/L. USGS geology rates 49% of the county's land low radon potential.

Next door, the shares run from 4.9% in Payette County to 51.6% in Adams County, with Canyon County and Payette County below Gem County.

Gem County against Idaho, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Gem County
Gem County9920.2%1.9 pCi/LThis county
Idaho, pooled44 counties, pooled12,96141.5%Not pooled+21.3 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+15.5 points
Bear Lake Countyhighest in the state3278.1%7.8 pCi/L+57.9 points
Minidoka Countylowest in the state7215.3%1.8 pCi/L−4.9 points
Adams County, IDborders it3151.6%4.0 pCi/L+31.4 points
Valley County, IDborders it12827.3%2.3 pCi/L+7.1 points
Ada County, IDborders it3,03025.2%2.4 pCi/L+5.0 points
Boise County, IDborders it5822.4%2.0 pCi/L+2.2 points
Washington County, IDborders it6720.9%2.1 pCi/L+0.7 points
Canyon County, IDborders it56310.7%1.6 pCi/L−9.5 points
Payette County, IDborders it614.9%1.5 pCi/L−15.3 points
Where Gem County's reported results fell, 2008 to 2017, laboratory, beside Idaho and the United States
ResultGem County testsGem County shareIdaho shareU.S. shareAgainst Idaho
Under 2 pCi/L5454.5%31.5%39.6%+23.0 points
2 to 4 pCi/L2525.3%26.9%24.7%−1.6 points
4 pCi/L and above2020.2%41.5%35.7%−21.3 points
Gem County ranked among the 37 Idaho counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Twin Falls County27 of 3736924.1%2.4 pCi/L
Owyhee County28 of 373023.3%2.1 pCi/L
Boise County29 of 375822.4%2.0 pCi/L
Nez Perce County30 of 3714922.1%2.3 pCi/L
Washington County31 of 376720.9%2.1 pCi/L
Gem County32 of 379920.2%1.9 pCi/L
Boundary County33 of 374520.0%2.1 pCi/L
Jerome County34 of 376516.9%1.9 pCi/L
Minidoka County35 of 377215.3%1.8 pCi/L
Canyon County36 of 3756310.7%1.6 pCi/L
Payette County37 of 37614.9%1.5 pCi/L
Gem County ten-year laboratory totals, against Idaho's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIdaho, pooledChange from the row before
2008 to 20179920.2%1.9 pCi/L14.5 pCi/L41.5%+2.6 points
2007 to 20168517.6%1.9 pCi/L14.5 pCi/L40.8%−0.8 points
2006 to 20158718.4%1.9 pCi/L14.5 pCi/L41.3%+1.1 points
2005 to 20147517.3%1.8 pCi/L9.5 pCi/L41.1%First on file

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

Gem County, Geology

The ground under Gem County

Predicted

No class of ground holds half of Gem County on USGS's geologic map: 49.0% of its land is low radon potential, 19.3% high and 31.8% moderate. The map puts 49.0% of Gem County in the area it calls Seven Devils and Tri-State Uplands and 31.8% in Eastern Snake river plain and Malheur-Boise-King Section, with one smaller area beside them. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Gem County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Seven Devils and Tri-State UplandsColumbia River basalt flows.Low849.0%
Eastern Snake river plain and Malheur-Boise-King SectionBasalt flows.Moderate1031.8%
Northern Rocky Mountain ProvinceDiorite and granite of the Idaho batholith.High1219.3%

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

Gem County beside the ground around it

Idaho as a whole has more high-potential ground than Gem County: 50.7% of its land, against 19.3% here. Of the 7 counties that border it, 2 have more high-potential ground, Valley County the most at 100%.

Share of land by USGS radon potential: Gem County, the 7 counties bordering it and Idaho
AreaEPA zoneLow potentialModerate potentialHigh potential
Gem CountyZone 349.0%31.8%19.3%
Boise CountyZone 10.1%None99.9%
Payette CountyZone 211.7%88.3%None
Washington CountyZone 388.1%11.9%None
Valley CountyZone 1NoneNone100%
Adams CountyZone 384.7%0.3%15.1%
Canyon CountyZone 2None100%None
Ada CountyZone 2None88.6%11.4%
Idaho44 counties, pooled by land areaVaries8.0%41.3%50.7%

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

Local help

Gem County, Local resources

Radon testing and mitigation in Gem County

What Idaho's program says
Phone
800-445-8647
Email
radon@dhw.idaho.gov

What it means

Gem County, Questions

Questions about radon in Gem County

Are radon levels high in Gem County?

Over the 2008 to 2017 laboratory totals, 20.2% of the radon tests reported to CDC for Gem County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.9 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 31 reported a higher share; pooled, the state comes to 41.5%.

Which counties border Gem County?

Gem County borders 7 counties: Boise County, Payette County, Washington County, Valley County, Adams County, Canyon County and Ada County.

Products

Gem County, Products

Testing a home in Gem County

In Gem County, 20.2% of 99 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 41.5% pooled across Idaho. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Gem County.

Test kits and monitors3

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Best radon monitors for Gem County homes, compared

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Gem County, Bordering counties

Counties bordering Gem County

Calculated by Radon411

Gem County, Cities and towns

Cities and towns in Gem County

Gem County is growing: the Census Bureau puts it at 21,773 residents on July 1, 2025, up 13.0% from 19,275 in 2020. That works out to 39 people per square mile of land. Emmett, its one incorporated place, has 8,900 residents, 40.9% of the total. CDC's 99 reported tests for 2008 to 2017 work out to 4.5 per 1,000 residents (2025 estimate), close to Idaho's 6.4.

Emmett is the one incorporated place here; CDC publishes no figure by town, so it reads Gem County's.

Emmett, Gem County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Emmett8,900+15.1%40.9%

One incorporated place, 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).

Gem County, Homes

Homes in Gem County

Gem County is a place of houses on their own lots: 81% of its 7,788 homes are detached single-family houses, against 74% across Idaho. The homes are older than Idaho's as a whole: half were built before 1982 (1990 for Idaho), and 21% date from before 1960. Owners live in 77% of the occupied homes (Idaho: 72%), so for most households a test and a fix are their own to order.

Homes in Gem County, Idaho, 2019 to 2023
HomesGem CountyIdaho
Housing units7,788776,683
Detached houses81%74%
In buildings of 5 or more4%9%
Mobile homes11%7%
Built before 196021%18%
Built since 200032%35%
Middle year built19821990
Owner-occupied77%72%

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