What EPA's radon map says about Philadelphia County

Philadelphia County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Nationally that's the 32nd percentile for radon potential — Philadelphia County outranks 32% of every county EPA has rated.

Where Philadelphia County sits nationally

About 1,573,916 people live in Philadelphia County, Pennsylvania, spread over 134.325 square miles. Population density there runs about 11,717 people per square mile. Among counties sharing Philadelphia County's EPA zone, it outranks 99% of them by population. Geologically, Philadelphia County is grouped into EPA Region 3 alongside 244 other counties that share its rock and soil setting.

Zone vs. an actual test

Well clear of both the 1.3 pCi/L national indoor average and EPA's 4 pCi/L action level, Philadelphia County's Zone 3 prediction is the low end of the scale. A Zone 3 label describes Philadelphia County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Next steps for a home in Philadelphia County

Mitigation cost doesn't depend on Philadelphia County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Pennsylvania's state radon program

Philadelphia County's test kit answers today; a Airthings radon monitor keeps answering for Philadelphia County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.