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

EPA's own radon map rates Mountrail County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 75th percentile for radon potential — Mountrail County outranks 75% of every county EPA has rated.

How Mountrail County compares

Mountrail County, North Dakota is home to about 9,474 people across 1,825.163 square miles. Averaged across its land area, Mountrail County runs about 5 people per square mile. By population, Mountrail County is the 780th largest of every county sharing its EPA zone — the 27th percentile by population within that zone. EPA's geology-based Region 8 groups Mountrail County with 290 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Mountrail County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in Mountrail County specifically.

If Mountrail County tests above the action level

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

Where Mountrail County's figures come from

Mountrail County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Mountrail County carries, the zone explainer covers what it does and doesn't tell you about any one house.