What EPA's radon map says about Sioux County

EPA places Sioux 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. Rank it against the rest of the country and Sioux County lands in the 69th percentile for radon potential.

Where Sioux County sits nationally

About 3,713 people live in Sioux County, North Dakota, spread over 1,094.052 square miles. Population density there runs about 3 people per square mile. Among counties sharing Sioux County's EPA zone, it outranks 10% of them by population. EPA's geology-based Region 8 groups Sioux County with 290 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Sioux County

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Sioux County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Sioux County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Sioux County tests above the action level

Mitigation cost doesn't depend on Sioux 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

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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.