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Radon Levels in Pierce County, Washington

EPA puts Pierce County in Zone 3, its lowest radon zone, and most reported tests there come back low, though 4.3% of 420 (2020) reached 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

    4.3%

    14.7 pts below WA

    Pierce
    4.3%
    Washington
    19.0%

    420 tests, 2020

  • Median result

    0.7pCi/L

    Below action level

    Pierce
    0.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2020

  • Tests reported

    420

    4th of 10 by tests

    Pierce
    420
    Spokane
    721

    Reported to CDC before any fix, 2020

  • 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 Washington

    8 of 10

    Middle half

    Pierce
    4.3%
    Spokane
    40.6%

    By share, of 10 with 30+ tests

Read a result for Pierce County

Starts at Pierce County's median, 0.7 pCi/L

0.7pCi/L

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

EPA’s reading of 0.7 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. Pierce County's median reported result, 2020.

Interpret this reading

The data

Pierce County, At a glance

Pierce County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Pierce 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 98% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Pierce County, 2020

Share of reported tests at or above 4 pCi/L, by year, Pierce County
Share of reported tests at or above 4 pCi/L, by year, Pierce County
YearShare of reported tests at or above 4 pCi/L
201415.3%
201521.4%
20163.6%
20179.8%
20184.9%
201912.6%
20204.3%

2020: 4.3%. Across these years the share ran from 3.6% to 21.4%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 420 tests reported to CDC for Pierce County over 2020, 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: 2020. Measured data period: 2005 to 2020 (every CDC figure on file).

How to read these figures

Pierce County, Compared

Pierce County radon figures, compared

Calculated by Radon411

Only 18 of 420 radon tests reported for Pierce County in 2020 reached 4 pCi/L (4.3%). The median result, 0.7 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 22.0 pCi/L.

Across 37 Washington counties pooled together, 19.0% of tests reached that level, so Pierce County runs 14.7 points below its state. Against the national pool of 25.5%, the gap is 21.2 points lower. Its place in the state: 8th of 10 Washington counties with 30 or more tests for the same period.

Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 4.3% share point the same way here. Of 4 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 0.0% (Kitsap County) to 6.5% (Thurston County).

Below the action level, 354 tests (84.3%) came in under 2 pCi/L, against 67.6% statewide, and 48 tests (11.4%) fell between 2 and 4, against 13.3% statewide. Over 7 years of annual figures the share fell 11.0 points, from 15.3% in 2014 to 4.3% in 2020; its peak was 21.4% in 2015. USGS geology rates 98% of the county's land low radon potential.

The busiest year on file was 2016, with 1,030 tests reported; the quietest, 2015, had 140.

Share of reported tests at or above 4 pCi/L by year, Pierce County against Washington2014 to 2020, years with 30 or more tests: Pierce County 15.3% to 4.3%, the state's pooled share 19.0% in 2020.
Pierce CountyWashington, pooled
Share of reported tests at or above 4 pCi/L by year, Pierce County against Washington: data table
YearTestsPierce County, at or above 4 pCi/LWashington, pooled
201421515.3%15.0%
201514021.4%17.4%
20161,0303.6%16.6%
20176519.8%19.1%
20187554.9%16.1%
201984812.6%20.9%
20204204.3%19.0%
Pierce County against Washington, the United States and nearby counties, 2020
AreaTestsAt or above 4 pCi/LMedianDifference from Pierce County
Pierce County4204.3%0.7 pCi/LThis county
Washington, pooled37 counties, pooled2,78119.0%Not pooled+14.7 points
United States, pooled915 counties, pooled405,35525.5%Not pooled+21.2 points
Spokane Countyhighest in the state72140.6%2.7 pCi/L+36.3 points
Snohomish Countylowest in the state1021.0%0.2 pCi/L−3.3 points
Lewis County, WAborders it1070.0%15.6 pCi/L+65.7 points
Kittitas County, WAborders it520.0%1.0 pCi/L+15.7 points
Thurston County, WAborders it466.5%0.4 pCi/L+2.2 points
Yakima County, WAborders it575.3%0.7 pCi/L+1.0 points
King County, WAborders it5035.0%0.3 pCi/L+0.7 points
Mason County, WAborders it30.0%1.7 pCi/L−4.3 points
Kitsap County, WAborders it500.0%0.4 pCi/L−4.3 points
Where Pierce County's reported results fell, 2020, beside Washington and the United States
ResultPierce County testsPierce County shareWashington shareU.S. shareAgainst Washington
Under 2 pCi/L35484.3%67.6%51.6%+16.7 points
2 to 4 pCi/L4811.4%13.3%22.9%−1.9 points
4 pCi/L and above184.3%19.0%25.5%−14.7 points
Pierce County ranked among the 10 Washington counties with 30 or more tests, by share at or above 4 pCi/L, 2020
CountyRankTestsAt or above 4 pCi/LMedian
Spokane County1 of 1072140.6%2.7 pCi/L
Stevens County2 of 104537.8%1.9 pCi/L
Walla Walla County3 of 103420.6%1.5 pCi/L
Clark County4 of 1049017.6%1.2 pCi/L
Thurston County5 of 10466.5%0.4 pCi/L
Yakima County6 of 10575.3%0.7 pCi/L
King County7 of 105035.0%0.3 pCi/L
Pierce County8 of 104204.3%0.7 pCi/L
Snohomish County9 of 101021.0%0.2 pCi/L
Kitsap County10 of 10500.0%0.4 pCi/L
Pierce County radon tests by year, against Washington's pooled share
YearTestsAt or above 4 pCi/LMedianHighestWashington, pooledChange from the row before
20204204.3%0.7 pCi/L22.0 pCi/L19.0%−8.3 points
201984812.6%0.7 pCi/L51.2 pCi/L20.9%+7.7 points
20187554.9%0.7 pCi/L20.2 pCi/L16.1%−4.9 points
20176519.8%0.8 pCi/L25.6 pCi/L19.1%+6.2 points
20161,0303.6%0.5 pCi/L19.5 pCi/L16.6%−17.8 points
201514021.4%0.7 pCi/L49.2 pCi/L17.4%+6.1 points
201421515.3%0.9 pCi/L19.7 pCi/L15.0%First on file

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

Pierce County, Geology

The ground under Pierce County

Predicted

USGS's geologic map puts all of Pierce County's mapped land in one class: low radon potential. The map puts 56.8% of Pierce County in the area it calls Cascade Mountains and 41.7% in Puget Lowlands. USGS gives both a radon index of 6, in the low band (5 to 8).

USGS's geologic areas under Pierce County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Cascade MountainsNorthern Cascade Mountains are Mesozoic metamorphic rocks intruded by Mesozoic and Tertiary granitic rocks. Southern Cascade Mountains are composed primarily of Tertiary and Holocene volcanic rocks.Low656.8%
Puget LowlandsContinental and marine sediments overlain by sandy and silty glacial deposits.Low641.7%

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

Pierce County beside the ground around it

Across Washington 13.7% of the land is rated high; none of Pierce County's is. Of the 7 counties that border it, 2 have more moderate-potential ground, Yakima County the most at 80.3%.

Share of land by USGS radon potential: Pierce County, the 7 counties bordering it and Washington
AreaEPA zoneLow potentialModerate potentialHigh potential
Pierce CountyZone 398.4%NoneNone
King CountyZone 398.1%NoneNone
Lewis CountyZone 3100%NoneNone
Thurston CountyZone 396.8%NoneNone
Kitsap CountyZone 385.1%NoneNone
Mason CountyZone 395.0%NoneNone
Kittitas CountyZone 222.5%77.5%None
Yakima CountyZone 219.7%80.3%None
Washington38 counties, pooled by land areaVaries46.4%39.0%13.7%

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

Local help

Pierce County, Local resources

Radon testing and mitigation in Pierce County

What Washington's program says
Phone
360-236-3200
Email
doh.radon@doh.wa.gov

What it means

Pierce County, Questions

Questions about radon in Pierce County

Are radon levels high in Pierce County?

In 2020, 4.3% of the radon tests reported to CDC for Pierce County, Washington were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.7 pCi/L. Of 10 Washington counties with 30 or more tests for the same period, 7 reported a higher share; pooled, the state comes to 19.0%.

Which counties border Pierce County?

Pierce County borders 7 counties: King County, Lewis County, Thurston County, Kitsap County, Mason County, Kittitas County and Yakima County.

Products

Pierce County, Products

Testing a home in Pierce County

In Pierce County, 4.3% of 420 tests reported to CDC in 2020 reached 4 pCi/L, against 19.0% pooled across Washington. 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 Pierce County.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Pierce County homes, compared

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Pierce County, Bordering counties

Counties bordering Pierce County

Calculated by Radon411

Pierce County, Cities and towns

Cities and towns in Pierce County

The Census Bureau estimates 946,288 residents in Pierce County for July 1, 2025, 22,679 more than in 2020 (+2.5%). That works out to 567 people per square mile of land. Its largest town, Tacoma, has 229,816 residents, 24.3% of the total. CDC's 420 reported tests for 2020 work out to 0.4 per 1,000 residents (2025 estimate), close to Washington's 0.3.

From Tacoma to South Prairie, CDC publishes no figure by town: each reads Pierce County's.

The 12 largest cities and towns in Pierce County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Tacoma229,816+4.4%24.3%
Auburnextends beyond Pierce County86,301−2.2%Counted whole
Lakewood62,755−1.4%6.6%
Puyallup42,682−0.8%4.5%
University Place35,479+1.6%3.7%
Bonney Lake22,139+0.5%2.3%
Edgewood13,548+9.1%1.4%
Enumclawextends beyond Pierce County13,172+4.4%Counted whole
Gig Harbor12,630+4.5%1.3%
Fife11,061+0.7%1.2%
Sumner10,871+2.0%1.1%
DuPont9,778−3.3%1.0%
  • Milton (part)
  • Orting
  • Pacific (part)
  • Fircrest
  • Steilacoom
  • Buckley
  • Eatonville
  • Ruston
  • Roy
  • Carbonado
  • Wilkeson
  • South Prairie

24 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Pierce County is counted whole, so it has no share.

Pierce County, Homes

Homes in Pierce County

Of Pierce County's 365,748 homes, 66% are detached houses, against 62% across Washington; 18% are in buildings of five or more homes. Half of its homes were built before 1985, close to Washington's 1984: 20% date from before 1960 and 28% from 2000 or later. 65% of occupied homes are lived in by their owner (Washington: 64%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Pierce County, Washington, 2019 to 2023
HomesPierce CountyWashington
Housing units365,7483,262,667
Detached houses66%62%
In buildings of 5 or more18%22%
Mobile homes5%6%
Built before 196020%21%
Built since 200028%28%
Middle year built19851984
Owner-occupied65%64%

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