Quick Answer

Radon levels in Delaware County, Pennsylvania are high based on EPA Zone 1. 4 cities have documented radon testing data through PA Radon Hub. The EPA action level of 4 pCi/L is exceeded in approximately 39.9% of tested homes in this region.

Radon in Delaware County, Pennsylvania

Delaware County is classified as Zone 1 on the EPA Map of Radon Zones. This page aggregates radon risk data for every PA Radon Hub city in the county, explains the underlying geology, and connects homeowners with DEP-certified testing and mitigation professionals serving Delaware County.

Radon Risk in Delaware County

The dominant subsurface formation across PA Radon Hub cities in Delaware County is Piedmont / Reading Prong Transition. Radon is produced continuously in uranium-bearing bedrock, migrates through soil gas, and enters the built environment through foundation penetrations. Pennsylvania's combination of fractured bedrock, older housing stock, and pronounced stack effect during the heating season drives elevated indoor radon across most of the Commonwealth.

The EPA zone classification divides counties by predicted average indoor radon: Zone 1 predicts average indoor radon above 4.0 pCi/L, Zone 2 predicts 2.0–4.0 pCi/L, and Zone 3 predicts below 2.0 pCi/L. Zone classifications are population averages — individual home results can vary substantially. Delaware County's Zone 1 classification means the county has high baseline radon potential, but every home should be tested individually.

Cities We Serve in Delaware County

Chester, PA →

Zone 1 · 3.7 pCi/L avg · 41.6% exceedance

High radon risk from Piedmont metamorphic rock and Reading Prong transitional geology in Delaware County. Chester's older urban housing stock with minimal foundation sealing amplifies radon entry from the uranium-bearing bedrock below.

Marcus Hook, PA →

Zone 1 · 3 pCi/L avg · 33.8% exceedance

Moderate-to-high radon risk at the Piedmont-Coastal Plain transition where Wissahickon schist dips beneath Cretaceous and Quaternary sediments near the Delaware River. Marcus Hook sits at the southern edge of Delaware County's Zone 1 designation, where the uranium-bearing Piedmont metamorphic basement is closer to the surface than in the coastal lowlands but deeper than on the upland plateau. Industrial-era housing stock with substandard foundations amplifies entry risk in this transitional geological zone.

Media, PA →

Zone 1 · 3.9 pCi/L avg · 41.7% exceedance

High radon risk from Wissahickon schist and associated Piedmont metamorphic rocks underlying Delaware County's upland plateau. Media, as the county seat, sits on Precambrian to early Paleozoic schist and gneiss with naturally elevated uranium content. The Wissahickon formation's foliated structure creates planar fracture pathways that channel radon gas efficiently toward the surface.

Ridley Park, PA →

Zone 1 · 4 pCi/L avg · 42.5% exceedance

High radon risk from Wissahickon schist underlying the Piedmont upland of southern Delaware County. Ridley Park sits on the same metamorphic basement that produces elevated radon throughout the county, but its planned Victorian-era borough layout — dense rows of pre-1920 homes on small lots — means a high concentration of older foundations with poor vapor barriers. The proximity to Crum Creek has cut into the schist, reducing soil cover and bringing uranium-bearing rock closer to foundation level.

Radon and Home Sales in Delaware County

Radon disclosure expectations and pre-sale testing practices vary across Pennsylvania, but Delaware County buyers and lenders increasingly request results during the inspection contingency period. Sellers often mitigate ahead of listing to avoid renegotiation when post-inspection results return high.

For a county-by-county breakdown of disclosure norms, mortgage requirements, and buyer/seller obligations, see the Radon and Home Sales in Pennsylvania guide.

SB 760 School Testing Mandate in Delaware County

Pennsylvania Senate Bill 760 requires radon testing in every public school building constructed before 2014 that sits in an EPA Zone 1 county. Initial testing must be completed during the 2026–2027 academic year under ANSI-AARST MA-MFLB protocol, with mitigation required within six months of any confirmed result at or above 4.0 pCi/L. For Delaware County school districts — which fall in Zone 1 — the mandate applies directly and will surface results across most pre-2014 buildings during the 2026–2027 window. For full compliance details, see the Pennsylvania Radon Compliance 2026 guide.

Find a DEP-Certified Radon Contractor in Delaware County

PA Radon Hub connects Delaware County homeowners with independent DEP-certified radon testing and mitigation professionals. All contractors verified against the PA Department of Environmental Protection Bureau of Radiation Protection directory.

For detailed pricing by foundation type across Pennsylvania, see the Pennsylvania Radon Mitigation Cost Guide.

Verify DEP certification status before hiring — search the PA DEP certified contractor directory.

County: Delaware County

PA Radon Hub is an independent informational resource. We do not perform radon testing or mitigation. We connect homeowners with DEP-certified professionals — verify any contractor's certification at dep.pa.gov/radon before hiring.

Frequently Asked Questions

What EPA radon zone is Delaware County in?

Delaware County is classified as Zone 1 — high radon potential — based on EPA radon zone mapping. 39.9% of tested homes across PA Radon Hub cities in this county exceed the 4.0 pCi/L action level.

What geological formations drive radon risk in Delaware County?

The dominant subsurface formation referenced across PA Radon Hub cities in Delaware County is Piedmont / Reading Prong Transition. Radon is produced by the decay of radium-226 in uranium-bearing bedrock and migrates into buildings through soil gas pathways — cracks, utility penetrations, and sump pits in the foundation.

Does SB 760 apply to public schools in Delaware County?

Yes if Delaware County schools fall in EPA Zone 1 and were built before 2014. Pennsylvania Senate Bill 760 requires public school buildings meeting those criteria to complete radon testing in the 2026–2027 academic year, with mitigation required within six months of any confirmed result at or above 4.0 pCi/L.