Radon in Chaudière-Appalaches: Thetford Mines, the Beauce (Saint-Georges), and the Risk Areas

Map of Canada with a pin on Chaudière-Appalaches — radon in Thetford Mines and the Beauce, Quebec

Chaudière-Appalaches shows one of the clearest radon signals in Quebec. The region sits on uranium-bearing Appalachian bedrock, and when the province screened its schools, the Beauce-Etchemin school board turned out to be the single most radon-affected board in Quebec — 14 schools above Health Canada's guideline of 200 Bq/m³, two of them above 600. But geology only tells you the odds, not your home's level. The only way to know whether your house in Thetford Mines, Saint-Georges or anywhere in the Beauce is elevated is a long-term test of at least 91 days.

See the Quebec radon map — measured results for every surveyed area, searchable by postal code.

Is Chaudière-Appalaches a high-radon area?

It is a region where elevated radon is well documented, but there is no official map that labels any street or town "high risk." Public-health authorities themselves describe the region's risk zones as not yet completely mapped, with measurement projects in homes and schools used to fill that gap. What we do have is hard evidence — the Beauce-Etchemin school results — and the underlying Appalachian geology, both of which point to a meaningful local radon potential. The practical takeaway: treat Chaudière-Appalaches as an area where testing is worth doing, and let your own 91-day measurement decide your number.

Why does Chaudière-Appalaches have a radon problem in the first place?

Radon is a colourless, odourless radioactive gas produced by the natural decay of uranium in rock and soil. Wherever the bedrock and overlying soils carry more uranium (and its decay-chain elements like radium and thorium), more radon is generated underground — and more of it can seep into buildings through foundation cracks, sump openings, and gaps around services.

Chaudière-Appalaches lies in the Appalachian belt of southeastern Quebec, a geologically complex zone of folded and faulted metamorphic and sedimentary rock. The region covers most of what is historically called the Beauce, with Lévis, Saint-Georges, Thetford Mines and Sainte-Marie among its main centres and a population of roughly 433,000. Several of these Appalachian rock units carry enough uranium and thorium to drive a higher-than-average radon potential at the surface — which is why both the documented school results and the provincial mapping work have focused attention here.

Geology raises or lowers the probability of a high reading across a neighbourhood; it does not set the number inside any individual house. Two homes on the same street can test very differently depending on foundation type, cracks, soil permeability, and ventilation. That is why a regional risk signal is never a substitute for testing your own home.

Is Thetford Mines a radon area — and isn't that an asbestos town?

Thetford Mines is the seat of the Les Appalaches regional county municipality and one of the best-known mining communities in Canada — historically the "asbestos capital," built on chrysotile (asbestos) deposits in the local serpentinite. It is a genuine mining region with a heavily mineralized geology, which is precisely why radon deserves attention here.

But it is important not to confuse the two hazards, because they are completely different:

  • Asbestos is a fibrous mineral. It poses a risk only when fibres are disturbed and inhaled — it is not a gas, it does not seep up through your basement floor, and a radon test does not measure it.
  • Radon is a radioactive gas produced by uranium decay in bedrock and soil. It enters through the foundation and accumulates indoors. Asbestos mining did not "create" the radon; the radon comes from uranium and radium in the surrounding Appalachian rock, independent of the asbestos itself.

So Thetford Mines being an old asbestos town is not the reason it can have radon — the reason is the uranium-bearing Appalachian geology underneath it. For homeowners, the action item is the same as anywhere else: run a long-term test and read your own number.

What happened with the Beauce-Etchemin schools?

This is the most concrete radon evidence the region has, and it is striking.

In 2011, Quebec's Ministry of Education (MELS) launched a province-wide operation to screen radon in primary and secondary schools, with detectors deployed during the heating season and analysed against Health Canada's 200 Bq/m³ guideline. The work was coordinated with the Ministry of Health (MSSS), Health Canada (which funded the detectors and lab analysis), school boards, and regional public-health directorates.

When the results came in, the Commission scolaire de la Beauce-Etchemin — the board serving Saint-Georges, Beauceville and surrounding Beauce communities — stood out as the most radon-affected school board in Quebec:

  • 14 schools recorded radon concentrations above 200 Bq/m³.
  • In two of those schools, levels exceeded 600 Bq/m³.
  • The board estimated corrective work — ventilation systems and chimney-style soil-depressurization measures — at roughly $70,000 across the affected buildings, and notified parents and staff of the readings for their facilities.

Health Canada's guideline applies to schools and workplaces, not just homes (any building with occupancy over four hours per day), so a school exceeding 200 Bq/m³ is held to the same line as a house. The reason schools were prioritized is simple: young children spend a large share of their day there.

The school result is a regional fingerprint, not a verdict on any home. It tells you the ground under the Beauce can generate enough radon to push occupied buildings well over the guideline — which is a strong reason for households in the same area to test. For the broader story of Quebec's school and daycare screening, see our deep-dive on radon in Quebec schools and daycares.

What about Saint-Georges and the rest of the Beauce?

Saint-Georges is the largest city in the Beauce and the urban heart of the area covered by the Beauce-Etchemin board — the same area where those school readings were recorded. That makes the surrounding MRCs (Beauce-Sartigan around Saint-Georges, Robert-Cliche around Beauceville, and La Nouvelle-Beauce around Sainte-Marie) a sensible place for homeowners to test, even though radon levels vary house by house.

A specific, public radon-awareness campaign from any individual Beauce municipality could not be independently confirmed for this article. In practice, residents are best served by the provincial guidance and the regional public-health direction rather than by a town-specific map, because — again — no complete risk-zone map of the area exists, and your foundation and soil decide your number.

For context on the broader province, our Quebec radon map and risk regions hub explains why "risk maps" are screening tools, not house-level predictions, and our pillar guide to radon in Quebec covers the provincial picture. If you are nearer the St. Lawrence end of the region, see radon in Lévis, the largest city in Chaudière-Appalaches.

How common is high radon in Quebec generally?

To put the regional signal in national context: the Evict Radon National Study's 2024 cross-Canada survey found that about 1 in 6 properties in Central Canada (Ontario and Quebec, ≈16.7%) sit at or above 200 Bq/m³, with roughly 18% of homes nationally at or above the guideline. A sub-regional figure for Chaudière-Appalaches specifically was not published in that survey.

These are prevalence numbers — the share of homes over the line — not a forecast for your address. They show that elevated radon is common enough across Quebec that "it probably doesn't affect me" is not a reliable assumption, especially in a region with documented school exceedances and uranium-bearing geology.

Radon in Chaudière-Appalaches: town and area signals

Town / area Risk signal / data Source
Beauce-Etchemin (Saint-Georges, Beauceville area) Most radon-affected school board in Quebec: 14 schools >200 Bq/m³, two >600 Bq/m³; ~$70,000 in corrective work MELS school screening, reported via Radio-Canada / Le Soleil / La Presse; CSSBE results report
Thetford Mines (Les Appalaches MRC) Appalachian mining region with mineralized geology; radon driven by uranium decay in bedrock (distinct from its asbestos history) Geological context; CNSC radon fact sheet (radon = uranium decay)
Chaudière-Appalaches (region-wide) No complete map of risk zones; home and school measurement projects underway; ~10% of Quebec lung-cancer deaths attributed to radon CISSS de Chaudière-Appalaches radon page
Central Canada (ON + QC) ~1 in 6 homes (≈16.7%) at/above 200 Bq/m³ Evict Radon National Study, 2024 cross-Canada survey

A risk signal in this table is a reason to test — it is never a reading for your home.

How do I actually test my home in Chaudière-Appalaches?

Health Canada and Quebec public-health authorities both recommend a long-term test of at least 91 days (about three months), ideally during the heating season (roughly fall through early spring) when homes are closed up and radon tends to accumulate. The 200 Bq/m³ guideline is defined against your average annual level, and only a long-term measurement gives a reliable estimate of it. Short-term "snapshot" tests swing widely with weather and ventilation and are not a basis for the guideline.

A managed long-term test is simple:

  1. Place a small alpha-track detector in the lowest lived-in level of your home — a basement family room, finished basement, or main floor if you have no basement — away from drafts, humidity and direct airflow.
  2. Leave it in place for the full 91+ days.
  3. Mail it to a C-NRPP-certified laboratory for analysis, and you receive your average radon concentration in Bq/m³.

RadonTest.ca's kit is built for exactly this: an alpha-track detector for a 91-day-plus measurement, analysed by a C-NRPP-certified Canadian lab, with prepaid return shipping and the option to have the analysis done entirely in Canada. (Note: no consumer radon kit is "Health Canada approved" — Health Canada sets the guideline and recommends C-NRPP-certified measurement; it does not certify retail products.)

What do I do if my level is above 200 Bq/m³?

If your long-term result comes back above 200 Bq/m³, Health Canada's current guidance is to reduce the level within one year — and sooner the higher your reading is. (Health Canada does not use a fixed tiered "two-year vs. one-year" schedule; the principle is simply that higher readings warrant faster action, targeting a final level as low as practicable.) There is no level considered completely risk-free, and radon is the second-leading cause of lung cancer in Canada after smoking.

The fix is well-established. Most homes are remediated with active soil depressurization — a certified contractor installs a sealed pipe and a quiet continuous fan that draws radon from beneath the foundation and vents it safely above the roofline, before it can enter your living space. It is the same principle as those "chimneys" the Beauce-Etchemin schools installed, scaled to a house. Use a C-NRPP-certified mitigation professional, then re-test to confirm the system worked.

For the step-by-step, read what to do if your radon level is above 200 Bq/m³, and for budgeting see our guide to radon mitigation costs in Canada.

Order your radon test kit → — all-in, analyzed in Canada, prepaid return shipping.

Frequently Asked Questions

Is Chaudière-Appalaches officially a high-radon region? There is no official map that designates the region or any town as "high risk," and public-health authorities describe the region's risk zones as not yet fully mapped. However, elevated radon is well documented here — most notably the Beauce-Etchemin school results — and the Appalachian geology supports a higher radon potential. It is a region where testing is clearly worthwhile, but only your own 91-day test reveals your home's level.

Why was the Beauce-Etchemin school board the most affected in Quebec? During Quebec's school radon screening, the Commission scolaire de la Beauce-Etchemin (serving Saint-Georges, Beauceville and the surrounding Beauce) had 14 schools above 200 Bq/m³ and two above 600 Bq/m³ — the highest count of any board in the province. The reason is the underlying uranium-bearing Appalachian bedrock, which generates more radon that can enter buildings.

Does Thetford Mines have radon because of asbestos mining? No. Asbestos and radon are unrelated hazards. Asbestos is a fibre that is dangerous when inhaled; radon is a radioactive gas produced by uranium decay in rock and soil. Thetford Mines can have elevated radon because of the uranium-bearing Appalachian geology beneath it, not because of its asbestos history. A radon test does not measure asbestos.

What radon level is acceptable in the Beauce? There is no radon level considered completely risk-free. Health Canada's action guideline is 200 Bq/m³: above that, you should reduce the level within one year, sooner if the reading is high. The guideline is the same everywhere in Canada, including Saint-Georges, Thetford Mines and the rest of Chaudière-Appalaches.

How long does a proper radon test take? At least 91 days (about three months), ideally during the heating season. Health Canada's 200 Bq/m³ guideline is based on your average annual level, and only a long-term alpha-track test gives a reliable estimate. Short-term tests are not a substitute.

My neighbour tested low — do I still need to test? Yes. Radon levels vary significantly from house to house, even next door, because of differences in foundation, cracks, soil and ventilation. A neighbour's low result does not tell you your number. The only way to know your home's level is to test your own home.

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