Radon levels in Grand Isle County, Vermont
LowEPA Zone 3Predicted long-term basement average of 1.5 pCi/L (model estimate) across 5 ZIP codes - about 17% below the US average of 1.8, close to the Vermont average of 1.7. Ranked #13 of 14 Vermont counties.
Test Grand Isle County, VT once anyway - radon varies house to house
The predicted basement average here is 1.5 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.
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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. Measured state test results are shown separately below, labeled with their source and years. How the numbers work.
1.5 ± 0.06
pCi/L predicted basement mean (model SD)
0.8 ± 0.07
pCi/L predicted upstairs (above-ground) mean
1.4-1.6
range of ZIP-level basement predictions in the county
Measured radon tests in Grand Isle County (Vermont Department of Health, 1994-2025)
Actual results from home radon tests reported to the state, separate from the model estimate above. Coverage: 1994-2025.
- Results ≥ 4 pCi/L
- 21%
- Sample
- 471 residences tested
| Figure | Model (predicted) | State tests (measured) |
|---|---|---|
| Mean, pCi/L | 1.5 basement | - |
| Share ≥ 4 pCi/L | not a model output | 21% |
The model and the state test data land within a few tenths of a pCi/L of each other here; the model estimates a long-term basement average while the tests are voluntary, mostly short-term results.
Source: VT Data - Radon Tests by Town, Vermont Department of Health, Environmental Public Health Tracking. Public Vermont Department of Health data. Method and download.
What this means for Grand Isle
The typical Grand Isle County home is predicted below 2 pCi/L, the lowest band. That is the best case an area can show - but it describes the average house, and the ZIP-level predictions within the county still span 1.4 to 1.6 pCi/L.
The 1993 EPA zone (3) and the 2001-2021 model agree for Grand Isle. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.
Comparable Vermont counties: Addison County (1.6), Franklin County (1.6), Chittenden County (1.4), Lamoille County (1.8). The state's highest is Bennington County at 2.0 pCi/L.
ZIP codes in Grand Isle County
Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.
| ZIP | Basement | Upstairs | Grade |
|---|---|---|---|
| 05458 | 1.5 ± 0.06 | 0.8 | Low |
| 05440 | 1.5 ± 0.06 | 0.8 | Low |
| 05486 | 1.6 ± 0.05 | 0.8 | Low |
| 05474 | 1.4 ± 0.06 | 0.7 | Low |
| 05463 | 1.5 ± 0.06 | 0.8 | Low |
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.
Grand Isle County radon questions
- Is radon high in Grand Isle County, Vermont?
- Low. The model predicts a long-term basement average of 1.5 pCi/L in Grand Isle County (about 17% below the US average of 1.8 and close to the Vermont average of 1.7). That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Ranked 13 of 14 Vermont counties.
- What do actual radon tests show in Grand Isle County?
- Vermont Department of Health data covering 1994-2025 (471 tested residences) shows 21% of results at or above the 4 pCi/L action level. These are voluntary home tests, so they skew toward basements and toward homes where radon was suspected; the model's predicted long-term basement average for the county is 1.5 pCi/L.
- Should I test for radon in Grand Isle County?
- Yes, once. The EPA recommends testing every home regardless of area, and the model's ZIP-level predictions in Grand Isle County already range from 1.4 to 1.6 pCi/L. A short-term kit costs little and settles the question for your house.
- What does EPA Radon Zone 3 mean for Grand Isle County?
- Zone 3 - low potential (< 2 pCi/L). The zone map dates from 1993 and classifies whole counties. The 2001-2021 model agrees with the zone here. Neither replaces a test of your own home.
- How much does radon mitigation cost in Grand Isle County?
- A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Vermont 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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