What EPA's radon map says about Armstrong County

EPA places Armstrong County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Armstrong County ranks higher in radon potential than 92% of rated counties (the 92nd percentile).

Where Armstrong County sits nationally

About 63,679 people live in Armstrong County, Pennsylvania, spread over 653.321 square miles. Population density there runs about 97 people per square mile. Among counties sharing Armstrong County's EPA zone, it outranks 75% of them by population. Armstrong County falls in EPA Radon Region 3, one of 245 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Armstrong County

Armstrong County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in Armstrong County specifically.

Next steps for a home in Armstrong County

Mitigation cost doesn't depend on Armstrong 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

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

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Armstrong County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.