What EPA's radon map says about Sanborn County

EPA places Sanborn 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. That puts Sanborn County in the 68th percentile nationally for radon potential — higher than 68% of the counties EPA has rated.

How Sanborn County compares

About 2,392 people live in Sanborn County, South Dakota, spread over 569.242 square miles. Averaged across its land area, Sanborn County runs about 4 people per square mile. Among counties sharing Sanborn County's EPA zone, it outranks 5% of them by population. EPA's geology-based Region 8 groups Sanborn County with 290 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Sanborn County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. That doesn't mean every Sanborn 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 Sanborn County tests above the action level

Mitigation cost doesn't depend on Sanborn 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 South Dakota's state radon program

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

Sanborn 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.