What EPA's radon map says about Cass County

EPA's own radon map rates Cass County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts Cass County in the 97th percentile nationally for radon potential — higher than 97% of the counties EPA has rated.

How Cass County compares

About 200,945 people live in Cass County, North Dakota, spread over 1,764.935 square miles. Population density there runs about 114 people per square mile. Among counties sharing Cass County's EPA zone, it outranks 91% of them by population. EPA's geology-based Region 8 groups Cass County with 290 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Cass County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Cass County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Cass County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

If Cass County tests above the action level

Mitigation cost doesn't depend on Cass 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 North Dakota's state radon program

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

Cass 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.