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Radon Levels in Penobscot County, Maine

EPA puts Penobscot County in Zone 1, its highest radon zone, and 16.4% of its 1,491 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    16.4%

    21.2 pts below ME

    Penobscot
    16.4%
    Maine
    37.6%

    1,491 tests, 2008 to 2017

  • Median result

    0.8pCi/L

    Below action level

    Penobscot
    0.8 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,491

    3rd of 16 by tests

    Penobscot
    1,491
    Cumberland
    4,076

    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 Maine

    16 of 16

    Lowest quarter

    Penobscot
    16.4%
    York
    48.4%

    By share, of 16 with 30+ tests

Read a result for Penobscot County

Starts at Penobscot County's median, 0.8 pCi/L

0.8pCi/L

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

EPA’s reading of 0.8 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. Penobscot County's median reported result, 2008 to 2017.

Interpret this reading

The data

Penobscot County, At a glance

Penobscot County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Penobscot 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: Moderate across 66% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Penobscot County, 2008 to 2017, laboratory
Under 2 pCi/L: 72%2 to 4 pCi/L: 12%4 pCi/L and above: 16%

Of 1,491 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Penobscot County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1,06471.4%
2 to 4 pCi/L18212.2%
4 pCi/L and above24516.4%
What these figures count

These are the 1,491 tests reported to CDC for Penobscot 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

Penobscot County, Compared

Penobscot County radon figures, compared

Calculated by Radon411

Penobscot County's 1,491 reported tests over the 2008 to 2017 laboratory totals had a middle value of 0.8 pCi/L and a maximum of 42.6 pCi/L, and 16.4% reached 4 pCi/L. Maine as a whole (16 Maine counties, pooled) comes to 37.6%: 21.2 points higher than here.

Among its state's counties it ranks 16th of 16 Maine counties with 30 or more tests for the same period. Statewide for the same period, York County reported the highest share (48.4%) and Somerset County the lowest (18.8%).

Below the action level, 1,064 tests (71.4%) came in under 2 pCi/L, against 41.4% statewide, and 182 tests (12.2%) fell between 2 and 4, against 21.0% statewide. CDC's ten-year totals for Penobscot County went from 1,330 tests (2005 to 2014) to 1,491 (2008 to 2017), the share going from 15.1% to 16.4%.

EPA's 1993 zone map puts Penobscot County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 66% of the county's land moderate radon potential.

Next door, the shares run from 18.8% in Somerset County to 47.7% in Piscataquis County.

CDC also counts 13 tests taken after mitigation in Penobscot County for the same period: tests in homes where a fix was already in.

Penobscot County against Maine, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Penobscot County
Penobscot County1,49116.4%0.8 pCi/LThis county
Maine, pooled16 counties, pooled11,82537.6%Not pooled+21.2 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+19.3 points
York Countyhighest in the state1,38948.4%3.7 pCi/L+32.0 points
Franklin Countylowest in the state14129.1%1.8 pCi/L+12.7 points
Piscataquis County, MEborders it4447.7%3.5 pCi/L+31.3 points
Aroostook County, MEborders it60845.1%3.5 pCi/L+28.7 points
Hancock County, MEborders it32739.1%2.6 pCi/L+22.7 points
Waldo County, MEborders it20932.1%2.3 pCi/L+15.7 points
Washington County, MEborders it5429.6%1.6 pCi/L+13.2 points
Somerset County, MEborders it8518.8%1.5 pCi/L+2.4 points
Where Penobscot County's reported results fell, 2008 to 2017, laboratory, beside Maine and the United States
ResultPenobscot County testsPenobscot County shareMaine shareU.S. shareAgainst Maine
Under 2 pCi/L1,06471.4%41.4%39.6%+30.0 points
2 to 4 pCi/L18212.2%21.0%24.7%−8.8 points
4 pCi/L and above24516.4%37.6%35.7%−21.2 points
Penobscot County ranked among the 16 Maine counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Hancock County6 of 1632739.1%2.6 pCi/L
Androscoggin County7 of 161,49736.9%2.8 pCi/L
Lincoln County8 of 1624635.8%2.5 pCi/L
Waldo County9 of 1620932.1%2.3 pCi/L
Kennebec County10 of 1669630.3%2.1 pCi/L
Sagadahoc County11 of 1628330.0%2.1 pCi/L
Washington County12 of 165429.6%1.6 pCi/L
Knox County13 of 1628729.6%2.3 pCi/L
Franklin County14 of 1614129.1%1.8 pCi/L
Somerset County15 of 168518.8%1.5 pCi/L
Penobscot County16 of 161,49116.4%0.8 pCi/L
Penobscot County ten-year laboratory totals, against Maine's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMaine, pooledChange from the row before
2008 to 20171,49116.4%0.8 pCi/L42.6 pCi/L37.6%−0.2 points
2007 to 20161,49116.6%0.8 pCi/L86.2 pCi/L37.6%+0.1 points
2006 to 20151,42116.5%0.8 pCi/L86.2 pCi/L37.6%+1.4 points
2005 to 20141,33015.1%0.7 pCi/L86.2 pCi/L36.6%First on file

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

Penobscot County, Geology

The ground under Penobscot County

Predicted

USGS's geologic map splits Penobscot County: 66.2% of its land is moderate radon potential and 4.0% high and 29.7% low. The map puts 66.2% of Penobscot County in the area it calls Moose River Lowlands/Central Maine Lowlands/Central Maine Highlands/Coastal Province and 21.9% in Central Maine Highlands, with 2 smaller areas beside them. USGS gives the first a radon index of 11, in the moderate band (9 to 11), and the second 8, in the low band (5 to 8).

USGS's geologic areas under Penobscot County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Moose River Lowlands/Central Maine Lowlands/Central Maine Highlands/Coastal ProvinceHeterogeneous metamorphic and igneous rocks.Moderate1166.2%
Central Maine HighlandsGlacial lake clay and marine clay.Low821.9%
Northern Maine LowlandsClastic and carbonate sedimentary rocks.Low87.8%
Central Maine HighlandsCalc-alkaline and alkaline granite and high grade metamorphic rocks.High143.9%

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

Penobscot County beside the ground around it

Maine as a whole has more high-potential ground than Penobscot County: 24.5% of its land, against 4.0% here. Of the 6 counties that border it, 5 have more high-potential ground, Hancock County the most at 43.4%.

Share of land by USGS radon potential: Penobscot County, the 6 counties bordering it and Maine
AreaEPA zoneLow potentialModerate potentialHigh potential
Penobscot CountyZone 129.7%66.2%4.0%
Piscataquis CountyZone 152.5%37.3%10.2%
Washington CountyZone 230.8%45.5%19.3%
Hancock CountyZone 11.5%49.1%43.4%
Aroostook CountyZone 163.8%25.7%10.4%
Waldo CountyZone 25.7%76.9%15.5%
Somerset CountyZone 145.6%52.3%2.1%
Maine16 counties, pooled by land areaVaries35.9%38.3%24.5%

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

Local help

Penobscot County, Local resources

Radon testing and mitigation in Penobscot County

What Maine's program says
Phone
207-287-5676
Email
radon.dhhs@maine.gov
Licensing of radon professionals
Under Maine law, only the owner or occupant of a residence or someone registered with the state to provide these services, may test for radon, install and/or advise on the installation of a radon reduction (mitigation) system.

What it means

Penobscot County, Questions

Questions about radon in Penobscot County

Are radon levels high in Penobscot County?

Over the 2008 to 2017 laboratory totals, 16.4% of the radon tests reported to CDC for Penobscot County, Maine were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.8 pCi/L. Of 16 Maine counties with 30 or more tests for the same period, 15 reported a higher share; pooled, the state comes to 37.6%.

Which counties border Penobscot County?

Penobscot County borders 6 counties: Piscataquis County, Washington County, Hancock County, Aroostook County, Waldo County and Somerset County.

Products

Penobscot County, Products

Testing a home in Penobscot County

In Penobscot County, 16.4% of 1,491 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 37.6% pooled across Maine. In Zone 1 the year-round level in Penobscot 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

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

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Penobscot County, Bordering counties

Counties bordering Penobscot County

Calculated by Radon411

Penobscot County, Cities and towns

Cities and towns in Penobscot County

The Census Bureau estimates 157,967 residents in Penobscot County for July 1, 2025, 5,793 more than in 2020 (+3.8%). That works out to 46 people per square mile of land. Its largest town, Bangor, has 32,518 residents, 20.6% of the total. Together its 3 incorporated places hold 31.5% of those residents; the other 68.5% live outside any of them. CDC's 1,491 reported tests for 2008 to 2017 work out to 9.4 per 1,000 residents (2025 estimate), close to Maine's 8.4.

From Bangor to Old Town, CDC publishes no figure by town: each reads Penobscot County's.

The cities and towns in Penobscot County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Bangor32,518+2.5%20.6%
Brewer9,636−0.4%6.1%
Old Town7,589+2.2%4.8%

3 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).

Penobscot County, Homes

Homes in Penobscot County

Of Penobscot County's 75,405 homes, 64% are detached houses, against 70% across Maine; 12% are mobile homes. Half of its homes were built before 1977, close to Maine's 1976: 34% date from before 1960 and 20% from 2000 or later. 70% of occupied homes are lived in by their owner (Maine: 74%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Penobscot County, Maine, 2019 to 2023
HomesPenobscot CountyMaine
Housing units75,405746,552
Detached houses64%70%
In buildings of 5 or more9%9%
Mobile homes12%8%
Built before 196034%35%
Built since 200020%20%
Middle year built19771976
Owner-occupied70%74%

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