Is Union County, SD a radon risk area?

EPA's own radon map rates Union County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Union County ranks higher in radon potential than 81% of rated counties (the 81st percentile).

Where Union County sits nationally

About 17,402 people live in Union County, South Dakota, spread over 460.757 square miles. Averaged across its land area, Union County runs about 38 people per square mile. Rank 608 by population within its EPA zone puts Union County at the 43rd percentile among zone peers. Union County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Union County

Where the national indoor average runs about 1.3 pCi/L, Union County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Union County will test well under the action level, and EPA's guidance is to test regardless of zone.

Testing and mitigation in Union County

Nothing about Union 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

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

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