What EPA's radon map says about Gem County

EPA places Gem 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. Gem County sits at the 14th percentile nationally for radon potential — above 14 of every 100 rated counties.

How Gem County compares

About 21,857 people live in Gem County, Idaho, spread over 559.774 square miles. That works out to roughly 39 people per square mile. Among counties sharing Gem County's EPA zone, it outranks 44% of them by population. Gem County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Gem County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. A Zone 3 label describes Gem County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Testing and mitigation in Gem County

Mitigation cost doesn't depend on Gem 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 Idaho's state radon program

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

More on how this number was built

Gem County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.