Oliver County, ND: EPA's radon zone, explained

EPA places Oliver 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. Nationally, Oliver County ranks higher in radon potential than 67% of rated counties (the 67th percentile).

Where Oliver County sits nationally

Oliver County, North Dakota is home to about 1,882 people across 722.404 square miles. Averaged across its land area, Oliver County runs about 3 people per square mile. By population, Oliver County is the 1033rd largest of every county sharing its EPA zone — the 3rd percentile by population within that zone. Geologically, Oliver County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Oliver County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. 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 Oliver County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Oliver County tests above the action level

For a Oliver County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find North Dakota's state radon program

For Oliver County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Oliver County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

Where Oliver County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Oliver County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.