What EPA's radon map says about Grand Isle County

EPA places Grand Isle County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Grand Isle County sits at the 4th percentile nationally for radon potential — above 4 of every 100 rated counties.

How Grand Isle County compares

About 7,528 people live in Grand Isle County, Vermont, spread over 81.771 square miles. That works out to roughly 92 people per square mile. Among counties sharing Grand Isle County's EPA zone, it outranks 14% of them by population. EPA's geology-based Region 1 groups Grand Isle County with 58 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Grand Isle County's predicted average sits below the national indoor average of about 1.3 pCi/L, well under EPA's 4 pCi/L action level. Even at Zone 3, Grand Isle County homes are not guaranteed a low reading — zone is a county-wide average, and EPA recommends testing every home regardless of zone.

Next steps for a home in Grand Isle County

Mitigation cost doesn't depend on Grand Isle 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 Vermont's state radon program

Grand Isle County's test kit answers today; a Airthings radon monitor keeps answering for Grand Isle 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

Grand Isle County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.