What EPA's radon map says about Navajo County

EPA places Navajo County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Navajo County ranks higher in radon potential than 60% of rated counties (the 60th percentile).

Where Navajo County sits nationally

About 109,516 people live in Navajo County, Arizona, spread over 9,949.496 square miles. Averaged across its land area, Navajo County runs about 11 people per square mile. Among counties sharing Navajo County's EPA zone, it outranks 82% of them by population. Navajo County falls in EPA Radon Region 9, one of 95 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Neither at the 4 pCi/L action level nor down at the roughly 1.3 pCi/L national indoor norm, Navajo County's Zone 2 prediction lands in the gap between the two. A county-wide moderate average, like Navajo County's, can still hide a specific house well above or below it — testing is what actually answers the question.

If Navajo County tests above the action level

Mitigation cost doesn't depend on Navajo 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 Arizona's state radon program

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

Navajo 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.