Pennsylvania · county radon data
Radon in Delaware County, Pennsylvania
21% of the 8,601 home radon tests on record here reached the EPA action level — toward the lower end of the state's tested counties, ranked #66 of 67 tested Pennsylvania counties.
What the numbers say
Delaware County sits 28 points below the Pennsylvania median (49% of tests over the limit across the state's counties). The median reading among its 8,601 reported tests was 1.9 pCi/L — and the single highest test on record reached 192.5 pCi/L, more than 48× the action level. EPA maps place the county in Radon Zone 1 — its highest-potential category, where average indoor screening levels are predicted above 4 pCi/L.
Why: the ground under Delaware County
Sits on Pennsylvania's folded Appalachian sedimentary rock — sandstones, shales, and carbonates that carry enough uranium that every county in the state has produced homes above the EPA action level. PA DEP calls radon a statewide concern. (Regional attribution here is well supported; unit-level detail is coarser — see methodology.)
Geology sources: PA DEP Radon Division · USGS OFR 93-292-C.
The housing stock factor
The median Delaware County home dates to 1957 — decades before radon-resistant new construction entered building codes. With 579,222 residents largely housed in that older stock, testing is the only way any individual household knows where it stands.
Radon by ZIP in Delaware County
Pennsylvania is one of the few states publishing actual test results at ZIP level (PA DEP residential data, 1986–2026) — county averages hide a lot; this doesn't.
| ZIP | Place | Tests | % ≥ 4 pCi/L | Max |
|---|---|---|---|---|
| 19052 | Lenni | 32 | 43.8% | 52.7 |
| 19063 | Media | 12,673 | 25.4% | 284.8 |
| 19064 | Springfield | 8,138 | 24.5% | 115.2 |
| 19041 | Haverford | 1,962 | 23.6% | 89.2 |
| 19373 | Thornton | 843 | 22.8% | 42.93 |
| 19060 | Garnet Valley | 2,011 | 20.7% | 34.1 |
| 19342 | Glen Mills | 98 | 20.4% | 58.2 |
| 19008 | Broomall | 5,843 | 20.2% | 134.7 |
| 19319 | Cheyney | 80 | 20% | 14.6 |
| 19083 | Havertown | 13,235 | 19.7% | 155 |
| 19070 | Morton | 1,557 | 18.8% | 48.8 |
| 19086 | Wallingford | 4,764 | 18.6% | 44.8 |
| 19010 | Bryn Mawr | 4,153 | 18.1% | 51.2 |
| 19073 | Newtown Square | 8,047 | 17.7% | 2021 |
| 19081 | Swarthmore | 3,156 | 17% | 72.4 |
| 19026 | Drexel Hill | 9,512 | 16.8% | 9999.9 |
| 19050 | Lansdowne | 6,265 | 16.1% | 77.1 |
| 19003 | Ardmore | 2,954 | 14.3% | 49.4 |
| 19018 | Clifton Heights | 4,942 | 13.8% | 109.3 |
| 19085 | Villanova | 1,525 | 13.2% | 52 |
| 19014 | Aston | 5,065 | 12.4% | 43.4 |
| 19078 | Ridley Park | 2,366 | 11.7% | 49.9 |
| 19061 | Marcus Hook | 3,944 | 11.6% | 148.1 |
| 19033 | Folsom | 1,523 | 9.4% | 29.6 |
| 19094 | Woodlyn | 775 | 9.2% | 22.1 |
| 19013 | Chester | 1,458 | 8.6% | 32 |
| 19017 | Chester Heights | 117 | 7.7% | 13.7 |
| 19076 | Prospect Park | 1,046 | 7.2% | 24 |
| 19074 | Norwood | 939 | 6.9% | 14.7 |
| 19022 | Crum Lynne | 373 | 6.7% | 26 |
| 19015 | Brookhaven | 3,045 | 5.8% | 47.3 |
| 19036 | Glenolden | 2,537 | 4.7% | 16.9 |
| 19079 | Sharon Hill | 1,106 | 4.7% | 105.7 |
| 19023 | Darby | 2,204 | 3.9% | 12.6 |
| 19043 | Holmes | 499 | 3.8% | 8.5 |
| 19032 | Folcroft | 1,272 | 2.8% | 14.9 |
| 19029 | Essington | 438 | 2.3% | 8 |
Delaware County in the Pennsylvania picture
| Delaware County | 21% over the limit | 8,601 tests |
| Pennsylvania's highest: Fulton County | 69.7% | 90 tests |
| Pennsylvania county median | 49% | 67 counties ranked |
| Share of all Pennsylvania tests from this county | 5.0% | |
Ranked nearby in Pennsylvania
- Bucks County — #63, 27.5% of 9,078 tests over the limit
- Montgomery County — #64, 27.2% of 14,749 tests over the limit
- McKean County — #65, 26.4% of 144 tests over the limit
- Philadelphia County — #67, 12.4% of 8,973 tests over the limit
(Ranking neighbors — counties adjacent in the Pennsylvania test ranking, not necessarily on the map.)
High test? Fixes and real pricing: the Pennsylvania mitigation cost guide. Every statistic here traces to the methodology (CDC EPHT (labs), 2008–2017; zones: EPA; year built & population: ACS 5-year; ZIP results: PA DEP).
Delaware County radon FAQ
- Is radon high in Delaware County?
- 21% of 8,601 home tests reported to the CDC came back at or above the EPA action level of 4 pCi/L — 28 points below the Pennsylvania county median of 49%, ranking #66 of 67 tested counties. EPA classifies the county as Zone 1.
- Does an older home in Delaware County mean more radon risk?
- The county's median home was built in 1957 — before radon-resistant construction practices entered building codes in the 1990s, so most of the housing stock has no built-in radon protection. Construction age changes the odds, not the answer: only a test tells you about your house.
- Where do these Delaware County numbers come from?
- 8,601 aggregated home tests in the CDC's Environmental Public Health Tracking dataset (CDC EPHT 2008-2017). Median reading: 1.9 pCi/L; the highest recorded test hit 192.5 pCi/L. How we handle the data, including its limits, is documented on our methodology page.
- Which ZIP codes in Delaware County test highest?
- In PA DEP's residential results (1986–2026): 19052 (Lenni) — 43.8% of 32 tests over the limit; 19063 (Media) — 25.4% of 12,673 tests over the limit; 19064 (Springfield) — 24.5% of 8,138 tests over the limit. Full ZIP table below.