What EPA's radon map says about Faulk County

EPA places Faulk 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. Faulk County sits at the 67th percentile nationally for radon potential — above 67 of every 100 rated counties.

Faulk County by the numbers

About 2,136 people live in Faulk County, South Dakota, spread over 981.713 square miles. Averaged across its land area, Faulk County runs about 2 people per square mile. Among counties sharing Faulk County's EPA zone, it outranks 4% of them by population. Faulk County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Faulk County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. 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 Faulk County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Faulk County tests above the action level

Mitigation cost doesn't depend on Faulk 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

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

More on how this number was built

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