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Radon Levels in Delaware County, Iowa

EPA puts Delaware County in Zone 1, its highest radon zone, and high results are common there: 50.0% of the 520 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

    50.0%

    8.5 pts below IA

    Delaware
    50.0%
    Iowa
    58.5%

    520 tests, 2008 to 2017

  • Median result

    4.0pCi/L

    Action level reached

    Delaware
    4.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    520

    44th of 99 by tests

    Delaware
    520
    Polk
    10,945

    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 Iowa

    80 of 99

    Lowest quarter

    Delaware
    50.0%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Delaware County

Starts at Delaware 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. Delaware County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Delaware County, At a glance

Delaware County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Delaware 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 Delaware County, 2008 to 2017, laboratory

Reported results by concentration band, Delaware County, 2008 to 2017, laboratory
Under 2 pCi/L: 24%2 to 4 pCi/L: 26%4 pCi/L and above: 50%

Of 520 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Delaware County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L12423.8%
2 to 4 pCi/L13626.2%
4 pCi/L and above26050.0%
What these figures count

These are the 520 tests reported to CDC for Delaware 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

Delaware County, Compared

Delaware County radon figures, compared

Calculated by Radon411

More than half: 50.0% of the 520 radon tests reported to CDC for Delaware County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 80th of 99 Iowa counties with 30 or more tests for the same period. That is 8.5 points below the 58.5% pooled from 99 Iowa counties.

The median result, 4.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 51.9 pCi/L. The rest split 23.8% under 2 pCi/L and 26.2% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 50.0% share point the same way here.

4 of its 6 bordering counties with figures ran higher, led by Fayette County at 62.7%; Linn County reported 39.7%. Statewide for the same period, Sioux County reported the highest share (84.2%) and Decatur County the lowest (25.9%).

CDC's ten-year totals for Delaware County went from 266 tests (2005 to 2014) to 520 (2008 to 2017), the share going from 52.3% to 50.0%.

Nationally, every county with a figure for the same period pools to 35.7%; Delaware County sits 14.3 points above it. CDC also counts 10 tests taken after mitigation in Delaware County for the same period: tests in homes where a fix was already in.

Delaware County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Delaware County
Delaware County52050.0%4.0 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled+8.5 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−14.3 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+34.2 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−24.1 points
Fayette County, IAborders it74662.7%5.6 pCi/L+12.7 points
Clayton County, IAborders it31062.6%5.8 pCi/L+12.6 points
Jones County, IAborders it55559.3%5.1 pCi/L+9.3 points
Buchanan County, IAborders it56451.2%4.1 pCi/L+1.2 points
Dubuque County, IAborders it3,77546.8%3.6 pCi/L−3.2 points
Linn County, IAborders it9,39539.7%3.0 pCi/L−10.3 points
Where Delaware County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultDelaware County testsDelaware County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L12423.8%21.8%39.6%+2.0 points
2 to 4 pCi/L13626.2%19.7%24.7%+6.5 points
4 pCi/L and above26050.0%58.5%35.7%−8.5 points
Delaware County ranked among the 99 Iowa counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Jackson County75 of 991,05652.7%4.1 pCi/L
Clinton County76 of 991,37552.7%4.3 pCi/L
Louisa County77 of 999652.1%4.1 pCi/L
Buchanan County78 of 9956451.2%4.1 pCi/L
Des Moines County79 of 9943651.1%4.2 pCi/L
Delaware County80 of 9952050.0%4.0 pCi/L
Black Hawk County81 of 993,22348.4%3.8 pCi/L
Dubuque County82 of 993,77546.8%3.6 pCi/L
Muscatine County83 of 9995446.5%3.7 pCi/L
Henry County84 of 9916846.4%3.4 pCi/L
Clarke County85 of 9912045.8%3.5 pCi/L
Delaware County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201752050.0%4.0 pCi/L51.9 pCi/L58.5%−0.3 points
2007 to 201631450.3%4.0 pCi/L51.9 pCi/L58.6%+0.5 points
2006 to 201529149.8%3.9 pCi/L51.9 pCi/L59.4%−2.5 points
2005 to 201426652.3%4.2 pCi/L51.9 pCi/L59.6%First on file

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

Delaware County, Geology

The ground under Delaware County

Predicted

USGS's geologic map puts all of Delaware County's mapped land in one class: high radon potential. The map puts 59.1% of Delaware County in the area it calls Iowan Surface and 32.4% in Loess-Covered Drift Plains, with one smaller area beside them. USGS gives the first a radon index of 12 and the second 13, both in the high band (12 to 17).

USGS's geologic areas under Delaware County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Iowan SurfacePre-Illinoian glaical deposits and loess.High1259.1%
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High1332.4%
Paleozoic PlateauOrdovician carbonate and Cambrian sandstone bedrock covered by varying amounts of Quaternary glacial deposits and loess.High138.5%

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

Delaware County beside the ground around it

On high-potential ground Delaware County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Buchanan County comes nearest at 100%.

Share of land by USGS radon potential: Delaware County, the 6 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Delaware CountyZone 1NoneNone100%
Clayton CountyZone 1NoneNone100%
Buchanan CountyZone 1NoneNone100%
Dubuque CountyZone 1NoneNone100%
Fayette CountyZone 1NoneNone100%
Jones CountyZone 1NoneNone100%
Linn CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Delaware County, Local resources

Radon testing and mitigation in Delaware County

What Iowa's program says
Phone
(515) 281-4928
Licensing of radon professionals
Iowa’s radon program approves applications for persons who wish to become certified to perform radon testing or credentialed to perform mitigation and laboratories that provide radon testing devices and analytical services.
Disclosure when a home is sold or rented
However, per Iowa Code chapters 543B.9 and 543B.18 and Iowa Administrative Code 193E Chapter 14 administered by the Iowa Real Estate Commission, a seller must disclose any known tests for the presence of radon and if yes, provide the date of last report and the result(s).

What it means

Delaware County, Questions

Questions about radon in Delaware County

Are radon levels high in Delaware County?

Over the 2008 to 2017 laboratory totals, 50.0% of the radon tests reported to CDC for Delaware County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.0 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 79 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Delaware County?

Delaware County borders 6 counties: Clayton County, Buchanan County, Dubuque County, Fayette County, Jones County and Linn County.

Products

Delaware County, Products

Testing a home in Delaware County

In Delaware County, 50.0% of 520 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 58.5% pooled across Iowa. In Zone 1 the year-round level in Delaware 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

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

Explore

Delaware County, Bordering counties

Counties bordering Delaware County

Calculated by Radon411

Delaware County, Cities and towns

Cities and towns in Delaware County

The Census Bureau estimates 17,674 residents in Delaware County for July 1, 2025, 218 more than in 2020 (+1.2%). That works out to 31 people per square mile of land. Its largest town, Manchester, has 5,357 residents, 30.3% of the total. CDC's 520 reported tests for 2008 to 2017 work out to 29.4 per 1,000 residents (2025 estimate), close to Iowa's 29.4.

From Manchester to Masonville, CDC publishes no figure by town: each reads Delaware County's.

The cities and towns in Delaware County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Manchester5,357+5.6%30.3%
Dyersvilleextends beyond Delaware County4,574+1.6%Counted whole
Edgewoodextends beyond Delaware County906−0.1%Counted whole
Earlville707−0.6%4.0%
Hopkinton618−0.3%3.5%
Delhi447+7.5%2.5%
Colesburg380−1.3%2.2%
Ryan346Level2.0%
Greeley210−1.4%1.2%
Dundee190−1.6%1.1%
Delaware139−0.7%0.8%
Masonville98−1.0%0.6%

12 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). A place that extends beyond Delaware County is counted whole, so it has no share.

Delaware County, Homes

Homes in Delaware County

Delaware County is a place of houses on their own lots: 87% of its 8,142 homes are detached single-family houses, against 72% across Iowa. Half of its homes were built before 1965, close to Iowa's 1971: 45% date from before 1960 and 16% from 2000 or later. Owners live in 82% of the occupied homes (Iowa: 72%), so for most households a test and a fix are their own to order.

Homes in Delaware County, Iowa, 2019 to 2023
HomesDelaware CountyIowa
Housing units8,1421,427,175
Detached houses87%72%
In buildings of 5 or more4%14%
Mobile homes3%3%
Built before 196045%39%
Built since 200016%21%
Middle year built19651971
Owner-occupied82%72%

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