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Radon Levels in Nez Perce County, Idaho

EPA puts Nez Perce County in Zone 3, its lowest radon zone, and 22.1% of its 149 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

    22.1%

    19.4 pts below ID

    Nez Perce
    22.1%
    Idaho
    41.5%

    149 tests, 2008 to 2017

  • Median result

    2.3pCi/L

    Below action level

    Nez Perce
    2.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    149

    15th of 37 by tests

    Nez Perce
    149
    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

    30 of 37

    Lowest quarter

    Nez Perce
    22.1%
    Bear Lake
    78.1%

    By share, of 37 with 30+ tests

Read a result for Nez Perce County

Starts at Nez Perce County's median, 2.3 pCi/L

2.3pCi/L

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

EPA’s reading of 2.3 pCi/L

Between 2 and 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 between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Nez Perce County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Nez Perce County, At a glance

Nez Perce County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Nez Perce 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 99% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Nez Perce County, 2008 to 2017, laboratory

Reported results by concentration band, Nez Perce County, 2008 to 2017, laboratory
Under 2 pCi/L: 38%2 to 4 pCi/L: 40%4 pCi/L and above: 22%

Of 149 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Nez Perce County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L5738.3%
2 to 4 pCi/L5939.6%
4 pCi/L and above3322.1%
What these figures count

These are the 149 tests reported to CDC for Nez Perce 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

Nez Perce County, Compared

Nez Perce County radon figures, compared

Calculated by Radon411

Nez Perce County's 149 reported tests over the 2008 to 2017 laboratory totals had a middle value of 2.3 pCi/L and a maximum of 60.0 pCi/L, and 22.1% reached 4 pCi/L. Idaho as a whole (44 Idaho counties, pooled) comes to 41.5%: 19.4 points higher than here.

Among its state's counties it ranks 30th 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, 57 tests (38.3%) came in under 2 pCi/L, against 31.5% statewide, and 59 tests (39.6%) fell between 2 and 4, against 26.9% statewide. CDC's ten-year totals for Nez Perce County went from 142 tests (2005 to 2014) to 149 (2008 to 2017), the share going from 16.9% to 22.1%.

EPA's 1993 zone map puts Nez Perce County in Zone 3, a predicted county average under 2 pCi/L. USGS geology rates 99% of the county's land low radon potential.

Next door, the shares run from 22.4% in Whitman County, WA to 40.0% in Idaho County.

Nez Perce County against Idaho, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Nez Perce County
Nez Perce County14922.1%2.3 pCi/LThis county
Idaho, pooled44 counties, pooled12,96141.5%Not pooled+19.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+13.6 points
Bear Lake Countyhighest in the state3278.1%7.8 pCi/L+56.0 points
Payette Countylowest in the state614.9%1.5 pCi/L−17.2 points
Lewis County, IDborders it650.0%3.8 pCi/L+27.9 points
Idaho County, IDborders it9040.0%2.9 pCi/L+17.9 points
Clearwater County, IDborders it3330.3%1.8 pCi/L+8.2 points
Wallowa County, ORborders it1526.7%1.1 pCi/L+4.6 points
Latah County, IDborders it15026.0%1.7 pCi/L+3.9 points
Whitman County, WAborders it5822.4%1.5 pCi/L+0.3 points
Asotin County, WAborders it60.0%1.3 pCi/L−22.1 points
Where Nez Perce County's reported results fell, 2008 to 2017, laboratory, beside Idaho and the United States
ResultNez Perce County testsNez Perce County shareIdaho shareU.S. shareAgainst Idaho
Under 2 pCi/L5738.3%31.5%39.6%+6.8 points
2 to 4 pCi/L5939.6%26.9%24.7%+12.7 points
4 pCi/L and above3322.1%41.5%35.7%−19.4 points
Nez Perce 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
Latah County25 of 3715026.0%1.7 pCi/L
Ada County26 of 373,03025.2%2.4 pCi/L
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
Nez Perce County ten-year laboratory totals, against Idaho's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIdaho, pooledChange from the row before
2008 to 201714922.1%2.3 pCi/L60.0 pCi/L41.5%+3.4 points
2007 to 201615018.7%2.0 pCi/L60.0 pCi/L40.8%−0.3 points
2006 to 201514719.0%2.0 pCi/L60.0 pCi/L41.3%+2.1 points
2005 to 201414216.9%2.0 pCi/L60.0 pCi/L41.1%First on file

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

Nez Perce County, Geology

The ground under Nez Perce County

Predicted

Most of the ground under Nez Perce County is one class on USGS's geologic map: 99.5% of its land is low radon potential, with 0.5% moderate. 99.5% of it lies in the area the map calls Seven Devils and Tri-State Uplands, to which USGS gives a radon index of 8, in the low band (5 to 8).

USGS's geologic areas under Nez Perce County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Seven Devils and Tri-State UplandsColumbia River basalt flows.Low899.5%

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

Nez Perce County beside the ground around it

Across Idaho 50.7% of the land is rated high; none of Nez Perce County's is. Of the 7 counties that border it, 4 have more high-potential ground, Clearwater County the most at 81.2%.

Share of land by USGS radon potential: Nez Perce County, the 7 counties bordering it and Idaho
AreaEPA zoneLow potentialModerate potentialHigh potential
Nez Perce CountyZone 399.5%0.5%None
Asotin County, WAZone 2None100%None
Lewis CountyZone 3100%NoneNone
Latah CountyZone 131.0%12.1%56.9%
Wallowa County, ORZone 3None100%None
Whitman County, WAZone 2None99.1%0.9%
Clearwater CountyZone 118.8%None81.2%
Idaho CountyZone 120.7%0.1%79.3%
Idaho44 counties, pooled by land areaVaries8.0%41.3%50.7%

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

Local help

Nez Perce County, Local resources

Radon testing and mitigation in Nez Perce County

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

What it means

Nez Perce County, Questions

Questions about radon in Nez Perce County

Are radon levels high in Nez Perce County?

Over the 2008 to 2017 laboratory totals, 22.1% of the radon tests reported to CDC for Nez Perce County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.3 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 29 reported a higher share; pooled, the state comes to 41.5%.

Which counties border Nez Perce County?

Nez Perce County borders 7 counties: Asotin County, WA, Lewis County, ID, Latah County, ID, Wallowa County, OR, Whitman County, WA, Clearwater County, ID and Idaho County, ID.

Products

Nez Perce County, Products

Testing a home in Nez Perce County

In Nez Perce County, 22.1% of 149 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 Nez Perce County.

Test kits and monitors3

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Best radon monitors for Nez Perce County homes, compared

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Nez Perce County, Bordering counties

Counties bordering Nez Perce County

Calculated by Radon411

Nez Perce County, Cities and towns

Cities and towns in Nez Perce County

The Census Bureau estimates 42,905 residents in Nez Perce County for July 1, 2025, 757 more than in 2020 (+1.8%). That works out to 51 people per square mile of land. Lewiston alone is home to 34,717 of them, 80.9% of the total. Together its 4 incorporated places hold 85.2% of those residents; the other 14.8% live outside any of them. Reported testing is thin here: 149 tests over 2008 to 2017, or 3.5 for every 1,000 residents (2025 estimate), where Idaho as a whole comes to 6.4.

From Lewiston to Peck, CDC publishes no figure by town: each reads Nez Perce County's.

The cities and towns in Nez Perce County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Lewiston34,717+1.4%80.9%
Lapwai1,251+3.2%2.9%
Culdesac417+0.7%1.0%
Peck174+4.8%0.4%

4 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).

Nez Perce County, Homes

Homes in Nez Perce County

Of Nez Perce County's 18,496 homes, 70% are detached houses, against 74% across Idaho; 10% are mobile homes. The homes are older than Idaho's as a whole: half were built before 1972 (1990 for Idaho), and 35% date from before 1960. 72% of occupied homes are lived in by their owner (Idaho: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Nez Perce County, Idaho, 2019 to 2023
HomesNez Perce CountyIdaho
Housing units18,496776,683
Detached houses70%74%
In buildings of 5 or more8%9%
Mobile homes10%7%
Built before 196035%18%
Built since 200015%35%
Middle year built19721990
Owner-occupied72%72%

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