Published
Is radon a problem in Ashton, Idaho? The local test record, the geology under it, and what to do
The short answer for this valley
Radon is not a hypothetical risk in Ashton — it is a measurable, local one. Idaho’s health department keeps the tally statewide:
“2 out of 5 Idaho homes have elevated radon levels.”
— Idaho Department of Health and Welfare, What is Radon? (page last updated 9-16-2026). Retrieved 5 October 2026
And the Ashton ZIP is not an exception to that statewide number — as the test record below shows, it leans worse. The gas itself is unglamorous: “It naturally comes from the breakdown of uranium in soil and rocks.” It seeps in through “small cracks in floors, walls, or around pipes”, and the house sits on it all winter with the windows shut.
Ashton's own test record
The state publishes a radon map by ZIP code, built from test results reported to the program. The rows behind it were last edited June 10, 2026. For the two ZIPs this site serves:
| ZIP code | Tests on record | Average result | Tests over the EPA guideline |
|---|---|---|---|
| 83420 — Ashton | 75 | 6.1 pCi/L | 34 of 75 |
| 83421 — Chester | 5 | too few to average | 3 of 5 |
Read that honestly in both directions: Ashton’s average test result, 6.1 pCi/L, sits above the 4.0 pCi/L EPA guideline, and 34 of the 75 tests on record came back over the line. But these are volunteer tests of finished houses, not a prediction for your lot: radon “can vary by location,” and as with the flood-zone map problem, the map tells you the neighborhood’s odds, never your address’s answer. Only a test does that.
Why the ground here produces it
Geology explains the pattern. The EPA/USGS Geologic Radon Potential map — in its 2025 revision — classifies the Ashton, Warm River, Chester, Drummond and Marysville area within the “Middle Rocky Mts./Yellowstone” province, described on the map layer as “Extrusive volcanics, rhyolite flows, variable composition.” Rhyolite country is uranium-bearing rock country; uranium decays to radium, radium decays to radon, and the gas works up through the soil under every foundation in the valley. “Variable composition” is the geologists’ way of saying the risk moves parcel to parcel — which is the map’s caveat, and the reason testing is the only arbiter.
The health math, in plain numbers
“Radon is the second leading cause of lung cancer in the U.S. and the number one cause among non-smokers. Radon exposure is responsible for approximately 21,000 lung cancer deaths annually.”
— Idaho Department of Health and Welfare, What is Radon? (page last updated 9-16-2026). Retrieved 5 October 2026
The state page also gives the most vivid conversion anyone has written:
“A radon reading of 4 pCi/L is the equivalent to smoking 8 cigarettes daily.”
— Idaho Department of Health and Welfare, What is Radon? (page last updated 9-16-2026). Retrieved 5 October 2026
Risk scales with level and with smoking history — the EPA assessment behind these figures (EPA 402-R-03-003) is the source of the lifetime-risk table the state republishes:
| Radon level (pCi/L) | of 1,000 smokers exposed for a lifetime, about this many lung cancers | of 1,000 non-smokers |
|---|---|---|
| 0.4 | 3 | — |
| 1.3 | 20 | 2 |
| 2.0 | 32 | 4 |
| 4.0 | 62 | 7 |
| 8.0 | 120 | 15 |
| 10 | 150 | 18 |
| 20 | 260 | 36 |
What a result means, and when to act
The action line is federal and simple:
“Radon levels higher than the Environmental Protection Agency’s (EPA) guideline of 4.0 pCi/L (picocuries per liter) should be mitigated.”
— Idaho Department of Health and Welfare, What is Radon? (page last updated 9-16-2026). Retrieved 5 October 2026
Below the line is not automatically “safe”: the EPA also suggests considering fixes between 2.0 and 4.0 pCi/L, especially if anyone in the home is at higher risk. The state’s action ladder, condensed: 0.4–1.3 is an average indoor level — retest every couple of years; 2.0–3.9 — consider a long-term test and consider fixing; 4.0 and higher — fix the home, yourself or with a professional.
Getting a test kit here
- Free state kits — one per address every two years — are listed as out of stock on the state page as of its September 16, 2026 update.
- Library lending — the Idaho Radon Library Lending Program lets you check a kit out free; the nearest participating branches are Idaho Falls Public Library (457 Broadway, 208-612-8460) and Valley of the Tetons — Victor Branch (56 N Main, 208-354-5528).
- Low-cost kits — order online with a credit card or by mail, or pick one up at a hardware or home improvement store.
- Professionals — a certified tester can be found through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB).
Technique is short: a short-term test runs 3–7 days and is best done in winter (closed-house conditions come naturally in January here); a long-term test, up to a year, gives the truest average. Test the lowest level where people actually spend time.
If the number comes back high
Mitigation is ordinary trades work with a fan and a pipe — and priced like it:
“DIY systems can cost $300–$600 in parts. There are many instructional videos on YouTube that can guide you through the process. Professional installation typically costs $1,500–$3,500.”
— Idaho Department of Health and Welfare, What is Radon? (page last updated 9-16-2026). Retrieved 5 October 2026
Limited-income owners have real options, listed by the state: HUD Community Development Block Grants (202-708-3587), HUD “203K” rehab loans (202-708-2121), EPA Environmental Justice grants (800-962-6215), and USDA home repair loans and grants. The state radon program itself answers questions at 800-445-8647 and radon@dhw.idaho.gov.
Renters, buyers, and people building now
Renting:
“Landlords aren’t required to test for or fix radon issues, but you can test the space yourself and discuss the results with them.”
— Idaho Department of Health and Welfare, What is Radon? (page last updated 9-16-2026). Retrieved 5 October 2026
Buying: the state’s advice is to ask for a radon test during the home inspection and, if levels are high, negotiate a mitigation system into the deal — at these mitigation prices, that is a $1,500–$3,500 conversation, not a dealbreaker.
Building: the cheapest version of radon control is the one installed while the slab is bare — see our page on radon-resistant construction for what to ask your builder for before pour day. Building new does not remove the testing step; it just tilts the odds.
Do it in this order
- Test the lowest lived-in level — short-term in winter, or long-term for the truest average. A borrowed library kit costs nothing.
- Confirm a high short-term result with a second test before spending mitigation money.
- Act on the ladder: 4.0 pCi/L and up, fix; 2.0–3.9, consider fixing — especially with smokers or kids in the house.
- Building instead? Put the radon features in at slab stage and budget the mitigation contingency elsewhere in the custom-home cost picture.
- Talk the whole envelope — air, moisture, insulation — through with us: (208) 656-1516.
Radon is the rare construction risk that is cheap to measure, plain to interpret, and fully fixable — the whole battle is remembering to test. This page is the reminder; the ZIP-level data says your odds here are worth the $0–$30 it takes to find out.
Common questions
Is radon a problem in Ashton, Idaho?
Yes - the local test record runs high. In ZIP 83420 (Ashton), the state's radon map dataset shows 75 tests on record with an average of 6.1 pCi/L, and 34 of those 75 tests came in over the EPA guideline of 4.0 pCi/L. Chester (83421) has 5 tests on record, 3 of them over. Statewide, 2 out of 5 Idaho homes have elevated radon levels.
What is a safe radon level?
There is no known fully safe level - the state page notes radon levels can change over time and EPA suggests considering fixes even between 2.0 and 4.0 pCi/L. The action threshold is 4.0 pCi/L: levels higher than the EPA guideline should be mitigated. For scale, average indoor radon nationally runs about 1.3 pCi/L.
What does 4 pCi/L mean in everyday terms?
Idaho's health department puts it bluntly: a radon reading of 4 pCi/L is the equivalent to smoking 8 cigarettes daily. That is the level at which mitigation is recommended - and Ashton's average test result of 6.1 pCi/L sits above it.
How do I test my Ashton home for radon?
Use a short-term test of 3 to 7 days, best done in winter with the house closed up, or a long-term test of up to a year for a truer average. Free state kits (one per address every two years) were out of stock as of the page's September 16, 2026 update; the Idaho Radon Library Lending Program lends kits through participating libraries including Idaho Falls Public Library (208-612-8460), and low-cost kits are sold online and at hardware stores.
How much does radon mitigation cost?
Per the Idaho health department, DIY systems can cost $300 to $600 in parts - the state itself points to instructional videos - while professional installation typically costs $1,500 to $3,500. Limited-income homeowners may qualify for help through HUD Community Development Block Grants, HUD 203(k) rehab loans, EPA Environmental Justice grants, or USDA home repair loans and grants.
Can I install a radon mitigation system myself?
Yes - the state page says DIY systems can cost $300 to $600 in parts and notes instructional videos exist to guide the process. The alternative is a certified professional found through the National Radon Proficiency Program or the National Radon Safety Board.
Do landlords have to test for radon in Idaho?
No. The state is explicit: landlords aren't required to test for or fix radon issues, but you can test the space yourself and discuss the results with them. Renters in the Ashton area should treat testing as their own job.
Should I test for radon when buying a home?
Yes - the Idaho health department's advice for buyers is to ask for a radon test during the home inspection and, if levels are high, negotiate to have a mitigation system installed. With professional installation typically running $1,500 to $3,500, it is a priced, fixable item rather than a reason to walk away.
Does building a new home solve the radon problem?
It lowers the odds if you ask for radon-resistant features before the slab is poured - a gravel layer, plastic sheeting, a labeled vent pipe, sealing, and an attic junction box. Idaho does not require them, so it is a buyer's request; see our radon-resistant construction page. Even with the features, the finished home should still be tested after move-in.
Why is radon high in the Ashton area specifically?
Geology. The EPA/USGS Geologic Radon Potential map (2025 revision) places Ashton, Warm River, Chester, Drummond and Marysville in the Middle Rocky Mountains/Yellowstone area, described as extrusive volcanics - rhyolite flows of variable composition. Uranium in that rock breaks down into radon, which moves up through the soil under foundations. The variability is why two houses on the same street can test very differently.
Where do radon deaths and risk numbers come from?
The Idaho page attributes its figures to the EPA: radon is the second leading cause of lung cancer in the U.S. and the number one cause among non-smokers, responsible for approximately 21,000 lung cancer deaths annually. The lifetime risk table smokers versus non-smokers comes from the EPA Assessment of Risks from Radon in Homes (EPA 402-R-03-003).
Who do I contact about radon in Idaho?
The Idaho Department of Health and Welfare's Environmental Health Program takes radon questions at 800-445-8647 or radon@dhw.idaho.gov. Certified measurement and mitigation professionals are listed through the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB).