Radon levels in Delaware: Low
The model predicts a population-weighted basement average of 1.3 pCi/L (model estimate) across Delaware's 3 counties - about 26% below the US average of 1.8 pCi/L. Above-ground floors average 0.8 pCi/L.
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.
0 / 3
EPA Zone 1 counties (0%)
1 / 2
Zone 2 / Zone 3 counties
0
counties predicted ≥ 4 pCi/L
0%
of ZIP codes predicted ≥ 4 pCi/L
Test Delaware once anyway - radon varies house to house
The predicted basement average here is 1.3 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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What the data says about radon in Delaware
According to the EPA zone map, 0 of Delaware's 3 counties are EPA Zone 1 (0%), 1 is Zone 2 and 2 are Zone 3. Most counties fall in Zone 3, the EPA's lowest-potential class (predicted screening average under 2 pCi/L). Treat the map as a coarse prior: it predates two decades of test data and never replaces a test in your own home.
The 2001-2021 national model predicts a population-weighted basement average of 1.3 pCi/L for Delaware (low range, 26% below the US average of 1.8). Of the 3 counties with predictions, 0 are predicted at or above 4 pCi/L, 0 in the 2-4 band and 3 below 2. The county range is narrow: from New Castle County at 1.29 to Sussex County at 1.42 pCi/L, a spread of only 0.13.
0% of the state's modeled ZIP codes are predicted at or above 2 pCi/L, and 0% at or above the 4 pCi/L action level - below the national shares of 4.2% and 48.7%. No ZIP in the state is predicted above 4 on average - but averages hide individual homes, which is why the EPA still asks everyone to test.
Delaware counties by predicted radon
Sorted highest to lowest predicted basement average (model estimate). 3 counties.
| County | Predicted basement | Upstairs | Grade | EPA zone | ZIPs |
|---|---|---|---|---|---|
| Sussex County | 1.4 pCi/L | 0.7 | Low | EPA Zone 3 | 22 |
| Kent County | 1.4 pCi/L | 0.7 | Low | EPA Zone 3 | 13 |
| New Castle County | 1.3 pCi/L | 0.9 | Low | EPA Zone 2 | 24 |
Radon levels in Delaware cities
The one most-populous Delaware place among the 1,000 largest US cities (Census incorporated places and CDPs), by population. City figures are ZIP-land-weighted means of the model's ZIP predictions (model estimate).
| City | Population | Predicted basement | Upstairs | Grade | ZIPs ≥ 4 |
|---|---|---|---|---|---|
| Wilmington | 71,675 | 1.1 pCi/L | 0.8 | Low | 0% |
Highest-radon ZIP codes in Delaware
The 10 Delaware ZIP codes with the highest predicted basement average (model estimate), out of 59 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.
| ZIP | County | Predicted basement | Upstairs | Grade |
|---|---|---|---|---|
| 19958 | Sussex County | 1.9 pCi/L | 0.8 | Low |
| 19977 | Kent County | 1.8 pCi/L | 1.0 | Low |
| 19709 | New Castle County | 1.7 pCi/L | 0.7 | Low |
| 19962 | Kent County | 1.6 pCi/L | 0.7 | Low |
| 19807 | New Castle County | 1.6 pCi/L | 1.1 | Low |
| 19938 | Kent County | 1.6 pCi/L | 0.8 | Low |
| 19930 | Sussex County | 1.5 pCi/L | 0.8 | Low |
| 19951 | Sussex County | 1.5 pCi/L | 0.7 | Low |
| 19734 | New Castle County | 1.5 pCi/L | 0.8 | Low |
| 19971 | Sussex County | 1.5 pCi/L | 0.8 | Low |
Delaware radon questions
- Is radon high in Delaware?
- Delaware's population-weighted predicted basement average is 1.3 pCi/L, about 26% below the US average of 1.8. 0 of its 3 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 0 are in the 2-4 "consider fixing" range and 3 are below 2. 0% of Delaware ZIP codes are predicted at 4 or higher.
- Which Delaware county has the highest radon?
- Sussex County has the highest predicted basement average in Delaware at 1.4 pCi/L (EPA Zone 3). The lowest is New Castle County at 1.3 pCi/L. These are area figures; individual homes in any county can test far higher.
- How many EPA Zone 1 counties are in Delaware?
- 0 of Delaware's 3 counties (0%) are EPA Zone 1 (highest potential), 1 are Zone 2 and 2 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.
- Should I test for radon in Delaware?
- Yes. Even though Delaware's predicted average is below 2 pCi/L, the EPA recommends every home be tested - radon varies house to house, and 0% of Delaware ZIP codes are still predicted at 2 pCi/L or higher.
Delaware radon program
State programs keep lists of certified testers and mitigators and sometimes run kit programs. We link only pages we could verify, and Delaware's program page did not respond when we checked, so start from the EPA state radon contacts page. Then read how to test and what mitigation costs.