Is radon high in Marathon County, Wisconsin?

Moderate. The model predicts a long-term basement average of 3.4 pCi/L in Marathon County (about 1.9× the US average of 1.8 and about 1.7× the Wisconsin average of 2.0). That is in the 2-4 pCi/L range where the EPA recommends considering mitigation. Ranked 2 of 72 Wisconsin counties.

Should I test for radon in Marathon County?

Yes, soon. With a predicted average of 3.4 pCi/L and at least one ZIP predicted at 5.0, many homes in Marathon County will test above the 4 pCi/L action level. Use a short-term kit first; if it reads 2 or higher, confirm with a long-term test or continuous monitor before deciding on mitigation.

What does EPA Radon Zone 1 mean for Marathon County?

Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and classifies whole counties. The newer model's predicted average of 3.4 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.

How much does radon mitigation cost in Marathon County?

A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Wisconsin quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.

Radon levels in Marathon County, Wisconsin

ModerateEPA Zone 1

Predicted long-term basement average of 3.4 pCi/L (model estimate) across 15 ZIP codes - about 1.9× the US average of 1.8, about 1.7× the Wisconsin average of 2.0. Ranked #2 of 72 Wisconsin counties.

Test Marathon County, WI - the EPA says "consider fixing" in this range

The predicted basement average here is 3.4 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.

Get a short-term test kit →Or track it with a continuous monitor

Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.

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Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.

3.4 ± 0.09

pCi/L predicted basement mean (model SD)

2.1 ± 0.08

pCi/L predicted upstairs (above-ground) mean

2.2-5.0

range of ZIP-level basement predictions in the county

What this means for Marathon

The typical Marathon County home is predicted in the 2-4 pCi/L band. The EPA's guidance for this range is to consider fixing, because there is no known safe level and roughly one home in several in a moderate area will test above 4.

Note that the EPA classifies Marathon County as Zone 1 while the newer model predicts 3.4 pCi/L. The zone map predates two decades of test data; where they disagree, we grade on the model but show both. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.

Comparable Wisconsin counties: Lafayette County (3.4), Grant County (3.3), Vernon County (3.0), Green County (3.0). The state's highest is Lafayette County at 3.4 pCi/L.

ZIP codes in Marathon County

Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.

ZIP	Basement	Upstairs	Grade
54401	3.4 ± 0.09	1.8	Moderate
54403	3.6 ± 0.10	2.5	Moderate
54476	3.2 ± 0.08	1.8	Moderate
54455	3.6 ± 0.09	2.7	Moderate
54411	2.6 ± 0.09	1.4	Moderate
54484	3.7 ± 0.08	2.2	Moderate
54426	3.5 ± 0.07	2.4	Moderate
54448	4.9 ± 0.15	2.8	High
54474	2.7 ± 0.06	1.7	Moderate
54421	2.2 ± 0.06	1.3	Moderate
54405	2.2 ± 0.05	1.4	Moderate
54440	3.6 ± 0.09	2.3	Moderate
54471	3.1 ± 0.07	2.1	Moderate
54427	3.3 ± 0.06	2.2	Moderate
54408	3.3 ± 0.07	2.2	Moderate

If your test comes back at 4 pCi/L or higher

Mitigation is a routine job: a fan-driven pipe that vents soil gas from under the slab to above the roofline, typically $800-$2,500 installed (typical range; local quotes vary). Use certified professionals: EPA find-a-professional. Read the full mitigation guide.

Marathon County radon questions

Is radon high in Marathon County, Wisconsin?: Moderate. The model predicts a long-term basement average of 3.4 pCi/L in Marathon County (about 1.9× the US average of 1.8 and about 1.7× the Wisconsin average of 2.0). That is in the 2-4 pCi/L range where the EPA recommends considering mitigation. Ranked 2 of 72 Wisconsin counties.
Should I test for radon in Marathon County?: Yes, soon. With a predicted average of 3.4 pCi/L and at least one ZIP predicted at 5.0, many homes in Marathon County will test above the 4 pCi/L action level. Use a short-term kit first; if it reads 2 or higher, confirm with a long-term test or continuous monitor before deciding on mitigation.
What does EPA Radon Zone 1 mean for Marathon County?: Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and classifies whole counties. The newer model's predicted average of 3.4 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.
How much does radon mitigation cost in Marathon County?: A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Wisconsin quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.

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