What EPA's radon map says about Marshall County

EPA's own radon map rates Marshall County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Marshall County ranks higher in radon potential than 76% of rated counties (the 76th percentile).

Marshall County by the numbers

About 9,950 people live in Marshall County, Kansas, spread over 900.178 square miles. Population density there runs about 11 people per square mile. Among counties sharing Marshall County's EPA zone, it outranks 28% of them by population. EPA's geology-based Region 7 groups Marshall County with 411 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Marshall County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Marshall County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Marshall 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.

Next steps for a home in Marshall County

Mitigation cost doesn't depend on Marshall 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 Kansas's state radon program

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

The methodology guide shows exactly which EPA and Census sources feed Marshall County's numbers. Whatever zone Marshall County carries, the zone explainer covers what it does and doesn't tell you about any one house.