Is Harding County, SD a radon risk area?

EPA places Harding County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 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 Harding County lands in the 33rd percentile for radon potential.

Where Harding County sits nationally

About 1,325 people live in Harding County, South Dakota, spread over 2,671.57 square miles. Population density there runs about 0 people per square mile. Rank 1016 by population within its EPA zone puts Harding County at the 2nd percentile among zone peers. EPA's geology-based Region 8 groups Harding County with 290 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's Harding County's Zone 2 prediction. Middle-of-the-pack doesn't mean risk-free for any one Harding County address — a moderate county average still leaves individual homes to test either side of it.

If Harding County tests above the action level

Nothing about Harding County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find South Dakota's state radon program

Harding County's test kit answers today; a Airthings radon monitor keeps answering for Harding County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

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