Is Clark County, ID a radon risk area?

EPA places Clark 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. Nationally that's the 66th percentile for radon potential — Clark County outranks 66% of every county EPA has rated.

Where Clark County sits nationally

About 794 people live in Clark County, Idaho, spread over 1,763.145 square miles. That works out to roughly 0 people per square mile. Rank 1064 by population within its EPA zone puts Clark County at the 0th percentile among zone peers. Clark County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Clark County

Where the national indoor average runs about 1.3 pCi/L, Clark County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. Some Clark County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Next steps for a home in Clark County

Nothing about Clark 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 Idaho's state radon program

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

Clark 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.