An Assessment of Residential Radon Potential in Thunder Bay Communities Proximate to Lake Superior

Section 1: Understanding the Radon Risk: A Primer for the Thunder Bay Resident

This section provides a foundational understanding of radon, outlining the nature of the hazard, its significant health implications, and the Canadian regulatory context that guides public health actions. This information is essential for interpreting the local data specific to Thunder Bay and making informed decisions regarding home safety.

1.1 The Invisible Hazard: Defining Radon and Its Pathways

Radon is a naturally occurring radioactive gas that is imperceptible to human senses; it is colorless, odorless, and tasteless.¹ It is generated through the natural, radioactive decay of uranium, an element found in trace amounts in virtually all rock and soil on Earth.³ As uranium breaks down, it forms a series of decay products, one of which is radium, which in turn decays to produce radon gas.

The primary and most significant source of radon in residential settings is the soil gas that exists in the ground beneath and around a home’s foundation.⁶ While certain building materials, such as granite, stone, brick, and cement, are derived from the earth and can contain uranium, they are not considered a significant source of radon in Canadian homes.⁸ A 2010 study by Health Canada on 33 common types of granite found that none released significant levels of radon.⁹ Therefore, the focus of risk assessment and mitigation must be on the interaction between a building and the underlying geology.

Because radon is a gas, it can move freely through pore spaces in soil and fractures in rock. It enters buildings through any available opening where the structure is in contact with the ground. Common entry points include ⁶:

• Cracks in foundation walls and concrete floor slabs.
• Construction joints, such as where the floor slab meets the foundation wall.
• Gaps around service penetrations for utilities like water pipes, sewer lines, and electrical conduits.
• Openings in the floor, such as floor drains and sump pits.
• The hollow cores of concrete block walls.

It is a critical misconception that only older, drafty homes are at risk. Any building, regardless of age or construction style—new or old, well-sealed or drafty, with or without a basement—has the potential to accumulate high levels of radon.² The amount of radon that enters and accumulates is a complex function of the local geology, the home’s specific construction, and the pressure dynamics between the building and the surrounding soil.

1.2 Health Implications of Long-Term Exposure

The health risks associated with radon are serious and well-documented. The International Agency for Research on Cancer (IARC), a part of the World Health Organization, classifies radon as a Group 1 carcinogen, meaning it is definitively known to cause cancer in humans.¹¹

When radon gas is inhaled, it undergoes further radioactive decay in the lungs, releasing alpha particles. These high-energy particles can damage the DNA of the cells lining the respiratory tract.¹¹ Over a prolonged period of exposure, this cellular damage can lead to the development of lung cancer. The overall risk to an individual is a function of three primary factors: the concentration of radon in the air, the duration of exposure, and the individual’s smoking habits.¹²

Radon exposure is the leading cause of lung cancer for people who have never smoked and the second leading cause overall, after smoking.¹¹ Health Canada estimates that approximately 16% of all lung cancer deaths in the country—more than 3,000 deaths each year—are attributable to radon exposure in the home.⁴

The risk is dramatically amplified for individuals who smoke. The combination of radon exposure and tobacco smoke creates a synergistic effect, meaning the combined risk is much greater than the sum of the individual risks. For example, data from the Ontario Lung Association indicates that a smoker exposed to high radon levels may have a 1 in 3 chance of developing lung cancer, compared to a 1 in 10 chance for a smoker not exposed to high radon.¹⁴ This makes radon awareness and mitigation especially critical for households with smokers.

1.3 The Canadian Regulatory Framework

In Canada, the approach to radon is guided by a framework developed by Health Canada in collaboration with the Federal Provincial Territorial Radiation Protection Committee (FPTRPC).¹⁵

The Canadian guideline for radon in indoor air is an action level of 200 becquerels per cubic metre ($Bq/m^3$).¹² A becquerel is a unit of radioactivity, representing one radioactive decay per second. Thus, a concentration of $200 Bq/m^3$ means that in every cubic metre of air, 200 radon atoms are decaying and emitting radiation every second. This guideline applies to the average annual concentration in the “normal occupancy area” of a building—any space where a person spends more than four hours per day, such as a finished basement, bedroom, or living room.⁶

It is crucial to understand that the $200 Bq/m^3$ guideline is not a demarcation of safety but rather an action level. Health Canada explicitly states that there is no level of radon that is considered risk-free.¹⁵ This position is based on the scientific consensus that any exposure to a carcinogen carries some level of risk. The guideline represents a level at which the risk is considered unacceptable from a public health perspective, and remedial action is strongly recommended. This approach is consistent with the internationally recognized ALARA (As Low As Reasonably Achievable) principle, which encourages individuals to reduce their exposure to radiation as much as is practicably possible, even if levels are already below the guideline.⁶ This contrasts with other jurisdictions; for example, the United States has an action level of $148 Bq/m^3$ ($4 pCi/L$), while the World Health Organization recommends a reference level between 100 and $300 Bq/m^3$.¹¹

The urgency for taking corrective action is directly related to the measured radon concentration ⁶:

• For levels between $200 Bq/m^3$ and $600 Bq/m^3$: Health Canada recommends that homeowners take corrective action within two years.¹²
• For levels above $600 Bq/m^3$: Corrective action should be taken within one year.¹²

In the province of Ontario, radon has been integrated into the building and warranty framework. The Ontario Building Code now requires builders of new homes to incorporate radon-preventative measures, such as a soil gas barrier and a properly sealed foundation.¹² Furthermore, the Tarion New Home Warranty program provides significant protection for new homeowners. Elevated radon levels exceeding the Health Canada guideline are considered a major structural defect, and Tarion may cover the costs of professional mitigation, up to a limit of $50,000, for homes within the first seven years of their warranty.¹² This classification elevates the issue from a homeowner maintenance concern to a recognized construction liability, providing a powerful recourse for new buyers and underscoring the importance of proper radon-resistant construction techniques.

Section 2: The Geological Underpinnings of Radon in the Lakehead Region

The elevated radon potential in Thunder Bay is not a random phenomenon but a direct consequence of the region’s ancient and complex geology. The city’s location on the Canadian Shield, combined with specific local rock formations rich in uranium, creates a persistent and widespread source for radon gas. Understanding this geological context is fundamental to comprehending the scale and distribution of the radon risk across the city and surrounding areas.

2.1 A Legacy of the Canadian Shield: The Regional Source Rock

Thunder Bay is situated on the Superior Province of the Canadian Shield, which is the largest and one of the oldest stable blocks of the Earth’s crust, known geologically as an Archean craton.¹⁸ This geological province is renowned for its vast mineral resources, a legacy of billions of years of geological processes.¹⁸ The bedrock in the Thunder Bay area is exceptionally old, with Archean Era rocks dated to approximately 2.7 billion years.¹⁹

The local geology is a complex mosaic of rock types. The city lies at a significant geological boundary between the very old (>2.5 billion years) granite and metamorphic rocks of the Archean Shield and overlying, younger (1.8 to 1.1 billion years old) layers of sedimentary and igneous rock.²⁰ The Archean basement consists primarily of granite, gneiss (a type of metamorphic rock), and greenstone volcanic belts.¹⁹

Granite is a key rock type in this context. As a naturally occurring igneous rock formed from the cooling of magma, granite universally contains trace amounts of naturally occurring radioactive elements, including uranium and thorium.⁸ The decay of these elements is the ultimate source of radon gas. While Health Canada has determined that granite used as a building material (e.g., countertops) is not a significant source of indoor radon, the vast expanse of uranium-bearing granitic and metamorphic rock underlying the region serves as a powerful, large-scale source for radon generation.⁹

2.2 Identifying High-Potential Formations and Uranium Occurrences

Geological surveys of the North Central Region of Ontario have identified specific formations and subprovinces in and around Thunder Bay that have a particularly high potential for uranium, and therefore, high radon production.

Two areas are explicitly identified as having the highest potential for uranium deposits: the Nipigon Basin area and the areas underlain by the Gunflint and Rove Formations.²² The Gunflint Formation, part of a larger sequence known as the Animikie Group, is a prominent geological feature in the region, stretching from Thunder Bay into the Mesabi Iron Range in Minnesota.¹⁹ It is composed of banded iron formation rocks, chert, and shale.¹⁹ Critically, this formation has been dated using Uranium-Lead (U-Pb) radiometric techniques to an age of approximately 1.88 billion years, a process that directly confirms the presence of the parent uranium isotopes necessary for radon generation.²³

Furthermore, the Quetico Subprovince, a major geological belt within the Superior Province, is documented as having an anomalously high background concentration of uranium, making it an important regional source rock for radon that can migrate into adjacent areas.²² An inventory of mineral occurrences in the region has cataloged numerous specific uranium deposits, many of which are high-grade vein-type deposits associated with the unconformity (the ancient erosional surface) between the Proterozoic and Archean rocks.²² These documented occurrences provide concrete evidence that the raw geological ingredient for a significant radon problem—uranium—is widespread throughout the region’s bedrock. The elevated radon levels measured in local homes are, therefore, a direct and predictable outcome of this specific geological endowment.

2.3 From Bedrock to Basement: Radon Transport and Emanation

The presence of uranium-bearing rock is only the first part of the equation. For radon to pose a risk, it must be able to travel from its source in the bedrock to the surface and into buildings. The geological history of the Thunder Bay region has created an efficient transport system for this gas.

The area sits at the edge of the Mid-Continent Rift System, an ancient tectonic feature where the North American continent began to pull apart approximately 1.1 billion years ago.²⁰ This process stretched and broke the hard, brittle rocks of the Canadian Shield, creating a network of deep-seated geological faults and fractures.²⁰ These structural features act as natural conduits or “superhighways” for radon gas, allowing it to bypass less permeable layers of rock and soil and move more readily toward the surface.²⁶ The association of high-grade uranium occurrences with fault and shear zones further highlights the role of these structures in concentrating and transporting radon’s parent elements.²²

Once the radon reaches the near-surface environment, the final stage of its journey is through the soil, which is composed of weathered material from the underlying bedrock. The physical properties of this soil, such as its permeability (how easily gas can pass through it), grain size, and moisture content, play a critical role in determining how much radon is released (emanated) from the soil particles and how quickly it is transported.²⁷ For instance, fine-grained, clay-rich soils can sometimes inhibit radon transport, but they can also trap the gas, especially when saturated with water, leading to a buildup of pressure that can force radon into a home.³¹ The structural geology (faults) and the surficial geology (soil type) are therefore just as important as the chemical geology (uranium content) in determining the ultimate radon risk at a specific location. This helps explain why radon levels can vary significantly over short distances, as a house built over a fracture zone may have a much higher radon ingress potential than a neighboring house on solid, unfractured bedrock.

Section 3: A Hyperlocal Analysis of Radon Concentrations in Thunder Bay

While the regional geology establishes a high potential for radon, public health studies provide the crucial data on actual indoor concentrations, revealing where this potential is being realized. The data for Thunder Bay demonstrates a clear and concerning trend of elevated radon levels that are not only significantly higher than provincial and national averages but also vary dramatically from one neighborhood to the next. This hyperlocal distribution of risk is a key finding for residents, particularly those living near the Lake Superior shoreline.

3.1 The City-Wide Anomaly: Contextualizing the Data

A pivotal study conducted during the winter of 2014-2015 by the Thunder Bay District Health Unit (TBDHU) provides the most detailed local picture of residential radon. The study distributed 468 long-term test kits to homes across the city.³³ The results showed that, on average, 16% of homes in Thunder Bay had radon concentrations exceeding Health Canada’s action guideline of $200 Bq/m^3$.⁵

To put this figure in perspective, the 16% prevalence rate is more than three times higher than the Ontario provincial average of 4.6% and more than double the Canadian national average of 6.9% reported in a 2012 Health Canada survey.⁴ While a more recent 2024 national survey suggests the Canadian average has risen to approximately 17.8%, the 2015 finding for Thunder Bay was already indicative of a significant local anomaly.²⁶ The TBDHU’s own analysis of the earlier Health Canada data for its specific health region had already pointed to an elevated risk, finding that 12% of homes in the district were above the guideline, a rate 50% higher than the Ontario average at the time.³³

This trend of elevated radon is not confined to the city limits but appears to be amplified in the surrounding rural and semi-rural areas. A subsequent TBDHU study in 2018 found an astonishing 65% of tested homes in the neighboring municipality of Oliver Paipoonge exceeded the guideline.⁵ Similarly, 17% of homes in Marathon, a community on the shore of Lake Superior, were found to be above the action level.⁵ This pattern suggests a gradient of increasing risk in less densely developed areas, a finding consistent with the 2015 Thunder Bay study, which noted that radon prevalence increased in the more rural parts of the city.³⁶

3.2 A Ward-by-Ward Breakdown: Identifying the Hotspots

The most striking finding of the 2015 TBDHU study was the extreme variation in radon prevalence among the city’s seven municipal wards. The risk is far from uniform, with some neighborhoods exhibiting rates comparable to the highest-risk areas in Canada, while others show virtually no issue. This demonstrates that a resident’s risk is more accurately predicted by their specific ward than by the city’s overall average.

The study identified several distinct high-risk zones ⁵:

• High-Risk Wards:
  • McIntyre Ward: Exhibited the highest prevalence, with 43% of tested homes measuring above $200 Bq/m^3$.
  • Neebing Ward: Showed a similarly alarming rate, with 30% of homes exceeding the guideline.
  • Red River Ward: Had 15% of homes above the action level.
  • Current River Ward: Had 13% of homes above the action level.
• Moderate- to Low-Risk Wards:
  • McKellar Ward: 6% of homes tested above the guideline.
  • Northwood Ward: 3% to 5% of homes tested above the guideline (reports vary slightly).¹⁴
  • Westfort Ward: Remarkably, 0% of the homes tested in this ward were found to have elevated radon levels.

This dramatic disparity means that public health messaging based on the 16% city average would dangerously understate the risk for a resident in McIntyre Ward (where the chance of having high radon was nearly 1 in 2 in the study) while simultaneously overstating it for a resident in Westfort Ward. Effective risk communication and public health interventions in Thunder Bay must therefore be geographically targeted at the ward level.

3.3 Focus on the Waterfront: Correlating Risk with Proximity to Lake Superior

By cross-referencing the ward-level radon data with municipal maps, a clear geographical pattern emerges that directly addresses the question of radon potential near Lake Superior.³⁸ The analysis confirms that wards with significant shoreline or proximity to the lake are among the highest-risk areas in the city.

The following table synthesizes the 2015 TBDHU study data with the geographical location of each ward, highlighting the correlation between radon risk and proximity to Lake Superior.

City Ward	Homes Tested	% with Radon > 200 Bq/m³	Geographical Location & Proximity to Lake Superior
McIntyre	82	43%	Northern, semi-rural ward located near the lake’s northern shoreline.
Neebing	47	30%	Southern, semi-rural ward with shoreline and proximity to the lake.
Red River	79	15%	Northeastern ward with extensive direct shoreline on Thunder Bay.
Current River	68	13%	North-central ward with direct shoreline on Thunder Bay.
McKellar	63	6%	Central ward, set back from the immediate shoreline but still in the eastern half of the city.
Northwood	75	3-5%	Central-western ward, located further inland from the lake.
Westfort	54	0%	Southwestern ward, located furthest inland from the high-risk shoreline areas.
Data Sources: 14

The data clearly illustrates that the wards directly on or near the Lake Superior shoreline (Current River, Red River, McIntyre, Neebing) all exhibit elevated radon prevalence, well above provincial and national averages. In contrast, the wards located further inland and to the west (Northwood, Westfort) show progressively lower risk, culminating in the 0% prevalence found in the most inland southwestern ward, Westfort.

This distinct spatial pattern, with a clear northeast-to-southwest gradient of decreasing risk, strongly suggests a direct link to the underlying geology discussed in Section 2. It is highly probable that the boundaries of the high-radon wards align with the surface expression of the high-uranium-potential geological formations, such as the Gunflint and Rove Formations. The public health data serves as a surface-level reflection of the subterranean geological map, providing a powerful, unified explanation for the observed radon distribution.

Section 4: Environmental Dynamics: The Lake Effect and Other Influences

The underlying geology provides the source of radon, but the amount that ultimately enters and accumulates in a home is heavily influenced by a complex interplay of environmental and building-specific factors. For communities near Lake Superior, the lake itself creates a unique microclimate that can significantly amplify the mechanisms of radon intrusion. This section explores how the “lake effect,” combined with soil conditions and housing characteristics, can create a “perfect storm” for elevated indoor radon levels.

4.1 Lake Superior’s Climatic Influence on Building Physics

Lake Superior, due to its immense size and thermal mass, exerts a powerful moderating influence on the local climate. This “lake effect” results in cooler air temperatures near the shore during the summer and relatively warmer temperatures in the fall and early winter compared to areas further inland.³⁹ This climatic influence can extend up to 16 kilometers from the shoreline.³⁹ While this effect is well-known for its impact on weather, it also has direct consequences for the physics of buildings along the coast.

A primary mechanism driving radon entry into homes is the thermal stack effect.⁴¹ During the heating season, the warm air inside a house is less dense than the cold air outside. This warm air rises and escapes through small openings in the upper levels of the home (e.g., attics, window frames). This outflow of air creates a slight negative pressure, or vacuum, in the lower levels of the house, particularly the basement. This pressure differential causes the house to act like a chimney, actively drawing in replacement air from the surrounding environment. A significant portion of this replacement air is pulled directly from the soil through the foundation, bringing soil gas—and any radon it contains—with it.

The proximity to Lake Superior can amplify this effect. During the cold heating season, when radon testing is most effective and levels are typically highest, the air temperatures near the lake are often colder and denser than those further inland.⁴⁰ This creates a larger temperature and pressure difference between the heated interior of a lakeside home and the outside air. A larger differential powers a stronger and more persistent stack effect, meaning the house “sucks” harder on the surrounding soil, potentially increasing the rate of radon infiltration compared to an identical home in a warmer, inland location.⁴²

4.2 The Role of Soil, Water, and Ice

The condition of the ground surrounding a home’s foundation is another critical variable. Precipitation, soil moisture, and ground frost play a significant role in controlling radon transport.

When the ground becomes saturated with water from heavy rain or snowmelt, the pore spaces between soil particles fill with water. This creates a barrier that is much less permeable to gas than dry soil, effectively inhibiting radon’s ability to escape harmlessly into the atmosphere.⁴³ Similarly, a layer of dense, wet snow or frozen ground in winter can create a “capping effect,” sealing the ground surface.³²

This capping action traps radon gas in the soil beneath and around the home’s foundation, causing its concentration and pressure to build up. With its primary upward escape route blocked, the pressurized soil gas follows the path of least resistance to a lower-pressure area. This path is often directly into the home’s basement, which is simultaneously creating a low-pressure zone via the stack effect.⁴² The combination of these two phenomena—the ground “pushing” radon due to the capping effect and the house “pulling” radon due to the stack effect—creates a powerful mechanism for radon intrusion. Given the potential for heavy lake-effect snow and saturated soils in the spring and fall, lakeside communities in Thunder Bay are particularly susceptible to this amplified push-pull dynamic.

4.3 The Built Environment: The Final Determinant

While geology and climate create the potential for high radon, the final concentration inside a specific home is ultimately determined by the characteristics of the building itself.⁴¹ Two houses built side-by-side on the same soil can have vastly different radon levels due to variations in construction and maintenance.

Key building factors include the type of foundation (e.g., full basement, slab-on-grade, crawl space), the integrity of the foundation (the number and size of cracks and openings), how well penetrations for pipes and utilities are sealed, and the overall ventilation rate of the home.²

The TBDHU study’s finding that homes built between the 1990s and early 2000s had the highest radon levels is particularly instructive.²⁷ This period corresponds to a time when construction practices were increasingly focused on creating more airtight, energy-efficient homes to reduce heating costs. While effective for energy conservation, this increased airtightness also reduces the natural rate of air exchange with the outdoors. If the rate of radon entry remains constant, but the rate of removal through ventilation decreases, the radon gas will accumulate to a higher equilibrium concentration inside the home. These homes were built after the push for energy efficiency but before the widespread adoption of radon-specific preventative measures in the Ontario Building Code, placing them in a potential “sweet spot” for radon accumulation.

The following table summarizes the key factors that converge to influence radon levels in lakeside environments like Thunder Bay.

Influencing Factor	Mechanism	Typical Effect on Indoor Radon
Uranium-Rich Geology	Source of radon gas through radioactive decay.	Increases the baseline radon potential of the soil.
Geological Faults	Provide high-permeability pathways for gas transport.	Facilitates efficient movement of radon from bedrock to the surface.
Lake-Cooled Air (Winter)	Increases indoor-outdoor temperature differential.	Amplifies the thermal stack effect, increasing the “pull” of radon into the home.
Winter Heating	Creates warm, rising air inside the home.	Drives the thermal stack effect, creating negative pressure in the basement.
Saturated/Frozen Soil	Creates a low-permeability “cap” on the ground surface.	Traps radon in the soil, increasing pressure and the “push” of radon into the home.
Foundation Cracks/Gaps	Provide direct entry points for soil gas.	Allows radon to bypass the solid foundation and enter the building.
Low Home Ventilation	Reduces the rate of air exchange with the outdoors.	Allows radon that enters to accumulate to higher concentrations.
Data Synthesis from: 20

In conclusion, the elevated risk in Thunder Bay’s lakeside communities is not attributable to a single factor. It is the result of a synergistic system where high-potential geology provides the source, the unique lake-influenced climate and soil conditions create a powerful push-pull intrusion mechanism, and the specific characteristics of each home determine its ultimate vulnerability.

Section 5: A Practical Guide to Radon Testing and Mitigation in Thunder Bay

Given the documented high radon potential and significant hyperlocal variability in Thunder Bay, moving from analysis to action is critical for protecting resident health. Because radon levels can differ dramatically even between adjacent homes, the only way to determine the risk in any specific building is to conduct a test.⁵ This section provides a practical, locally-focused guide for residents on how to test their homes, interpret the results, and take effective remedial action if necessary.

5.1 Empowering Homeowners Through Testing

Testing for radon is a simple and inexpensive process that can be undertaken by homeowners themselves or by hiring a certified professional.

Long-Term Testing is the Standard

Radon levels in a home are not static; they fluctuate constantly due to changes in weather, temperature, and ventilation patterns.¹ A short-term test of a few days may not capture the true average exposure. For this reason, Health Canada strongly recommends conducting a long-term test for a minimum of three months (91 days).¹ This duration is sufficient to average out short-term fluctuations and provide a reliable estimate of a home’s annual average radon concentration, which is the basis for the Canadian guideline.⁹ The ideal time to conduct this testing is during the heating season (fall and winter), as homes are typically more sealed, and the stack effect is strongest, leading to the highest and most representative radon concentrations.¹

Local Do-It-Yourself (DIY) Testing Options

Several accessible and affordable options are available for residents in the Thunder Bay area:

• EcoSuperior Environmental Programs: This local organization is a primary resource for radon testing. They sell long-term alpha track detector kits for $50, a price that includes the device, instructions, and the subsequent laboratory analysis fees.¹⁴ Kits can be ordered online for pickup.
• Public Library Loan Programs: In a progressive public health initiative, several libraries in Northwestern Ontario, including all branches of the Thunder Bay Public Library, offer digital radon detectors for loan to library card holders.¹⁶ These electronic monitors provide real-time and average readings, offering a convenient way for residents to screen their homes. Other participating libraries include those in Oliver Paipoonge, Nipigon, Red Rock, Dorion, and Marathon.¹⁶
• Hardware and Building Supply Stores: Long-term test kits can also be purchased at some local hardware stores or online from various certified organizations.¹²

When placing a test device, it is crucial to follow the instructions carefully. The device should be placed in the lowest level of the home that is regularly occupied for four or more hours per day (e.g., a basement family room or bedroom) and left undisturbed for the entire testing period.⁶

Hiring a Measurement Professional

For residents who prefer a professional service, the alternative is to hire a measurement professional certified by the Canadian National Radon Proficiency Program (C-NRPP).¹² These professionals are trained in proper testing protocols to ensure accurate and reliable results.

5.2 Interpreting Your Results and Taking Action

Once a long-term test is complete and the results are received from the lab, they should be compared to the Health Canada guideline.

• If the result is below $200 Bq/m^3$: No immediate action is required. However, given the ALARA principle, homeowners may still consider simple measures to further reduce levels. It is also good practice to re-test every few years or after any major renovations.
• If the result is between $200 Bq/m^3$ and $600 Bq/m^3$: Remedial action should be taken within two years.¹²
• If the result is above $600 Bq/m^3$: Remedial action should be taken within one year.¹²

It is important to remember that even very high radon levels can be successfully reduced. A high test result is not a reason to panic but a clear signal to take corrective action.⁴⁹ Radon mitigation systems are highly effective, often reducing indoor levels by over 80-90%, and can typically be installed in less than a day at a reasonable cost, generally ranging from $500 to $3,000.²⁷

5.3 Professional Solutions: Mitigation in the Lakehead

When radon levels are found to be above the guideline, the most common and reliable solution is the installation of an Active Soil Depressurization (ASD) system, also known as Sub-Slab Depressurization (SSD).⁹ This method involves inserting a small pipe through the foundation floor into the soil or gravel layer beneath. This pipe is connected to a fan, usually located in the attic or outside the home, which runs continuously. The fan creates a permanent low-pressure field under the foundation, constantly drawing radon-laden soil gas from beneath the home and safely venting it above the roofline before it has a chance to enter the living space.⁹

While sealing major cracks in the foundation and ensuring a sealed lid on sump pits are important supplementary measures, they are rarely sufficient on their own to solve a significant radon problem.² An ASD system is the gold standard for effective, long-term radon reduction.

To ensure a mitigation system is designed and installed correctly and effectively, it is essential to hire a C-NRPP certified mitigation professional.⁹ These contractors have the training and diagnostic tools to determine the best location for the suction point and the appropriate fan size for the home’s specific conditions.

Table 2: Directory of Radon Testing and Mitigation Resources in Thunder Bay

The following is a directory of local and regional resources for obtaining test kits and professional services.

Resource Category	Provider	Contact Information	Services Offered
DIY Test Kit Providers	EcoSuperior Environmental Programs	562 Red River Road, Thunder Bay, ON	Sells C-NRPP approved long-term alpha track test kits ($50, includes lab fees). Provides public education and workshops. 16
Public Library Loan Programs	Thunder Bay Public Libraries	All branches	Loans digital radon detectors to library members for short-term screening. 16
	Oliver Paipoonge Public Libraries	Murillo & Rosslyn Branches	Loans digital radon detectors. 16
C-NRPP Certified Professionals	Canada Radon	(807) 788-3245 | info@canadaradon.com	Certified for radon measurement and mitigation. 16
	EXP Services Inc.	(807) 623-9495 | kristof.karpiuk@exp.com	Certified for radon measurement. 16
	First General Services	(807) 623-1276 | mark.johnson@firstgeneral.ca	Certified for radon measurement. 16
	Northern Home Designs	(807) 344-4567 | northernhomedesigns@shaw.ca	Certified for radon measurement. 16
	Radon Safe Northwest Ltd.	(807) 626-3049 | stjarre@tbaytel.net	Certified for radon measurement. 16
	SASI Water	(807) 622-8880 | andrew@sasi.ca	Certified for radon measurement. 16
	TBT Engineering	(807) 624-5160 | dsteele@tbte.ca	Certified for radon measurement. 16
	Stantec	(807) 626-5640 | hwilson@tgcl.ca	Certified for radon measurement. 16
Note: The list of certified professionals is subject to change. Always verify current certification status through the C-NRPP website.

Section 6: Concluding Analysis and Strategic Recommendations

This report has synthesized geological data, public health studies, and environmental science to construct a comprehensive risk profile for residential radon in Thunder Bay, with a specific focus on communities proximate to Lake Superior. The evidence points to a clear and significant public health concern that requires targeted awareness and action from residents and policymakers.

6.1 Synthesized Risk Profile for Residents Near Lake Superior

The potential for elevated indoor radon levels in homes located within several blocks of the Lake Superior shoreline in Thunder Bay is significantly higher than provincial and former national averages. This conclusion is based on a convergence of multiple, compounding risk factors that create a uniquely challenging environment.

The heightened risk is not attributable to a single cause but is the result of a synergistic system comprising three primary elements:

1. Geological Predisposition: The city is founded upon the ancient, mineral-rich bedrock of the Canadian Shield. Specific geological units underlying the region, notably the Quetico Subprovince and the Gunflint and Rove Formations, are known to have high background levels of uranium, the ultimate source of radon gas.
2. Climatic Amplification: The microclimate created by Lake Superior directly influences the physics of radon intrusion. During the long heating season, colder lakeside air temperatures can amplify the thermal stack effect, causing homes to draw more forcefully on the surrounding soil. Simultaneously, lake-effect precipitation can lead to saturated or frozen ground, creating a “capping effect” that traps radon and increases subsurface gas pressure. This combination creates a powerful “push-pull” mechanism that drives radon into basements.
3. The Built Environment: The final indoor concentration is determined by a home’s specific construction, age, and maintenance. The extreme hyperlocal variability observed in the TBDHU study—with prevalence rates ranging from 43% in McIntyre Ward to 0% in Westfort Ward—underscores that while the environment creates the potential, the house itself determines the final exposure level.

The data from the 2015 TBDHU study confirms this risk is most pronounced in the wards with direct shoreline or a semi-rural character near the lake: McIntyre, Neebing, Red River, and Current River. Residents in these areas face a demonstrably higher probability of living in a home with radon concentrations that exceed the Canadian action guideline. Due to this extreme variability, predictive risk mapping is insufficient for individual decision-making. Therefore, individual home testing is not merely a recommendation but an essential health and safety measure for all residents in these high-potential areas.

6.2 Recommendations for Homeowners, Buyers, and Renters

Based on this analysis, the following actions are recommended for residents and stakeholders in Thunder Bay:

• For Current Homeowners:
  • Test Your Home: All homeowners, particularly those residing in the high-risk wards (McIntyre, Neebing, Red River, Current River) or in homes built between the 1980s and the early 2000s, should conduct a long-term radon test (minimum three months) during the heating season.
  • Mitigate if Necessary: If test results exceed $200 Bq/m^3$, contract a C-NRPP certified mitigation professional to install a radon reduction system.
  • Inform Yourself: Utilize local resources like EcoSuperior and the Thunder Bay District Health Unit to learn more about radon risks and solutions.
• For Prospective Home Buyers:
  • Make Radon Testing a Condition: A long-term radon test should be considered a standard and non-negotiable condition in any offer to purchase a home in Thunder Bay, akin to a professional home inspection. If time is a constraint, a short-term test can be used for screening, followed by a long-term test post-occupancy.
  • Inquire About Existing Systems: When viewing a property, ask if a radon mitigation system is already installed. If so, request documentation of its installation and post-mitigation test results to ensure it is functioning effectively.
• For Renters and Landlords:
  • Collaborate on Testing: Both tenants and landlords should be aware that high radon is a potential health hazard in rental properties. Public health units may respond to tenant complaints regarding high radon levels in a manner similar to other health hazards.³³ Open communication and collaborative testing are encouraged.
  • Landlord Responsibility: Landlords have a responsibility to provide a safe living environment, and addressing a confirmed high radon level falls within this purview.
• For Public Policy and Health Agencies:
  • Continue Targeted Awareness: The TBDHU and its partners should continue public awareness campaigns, using ward-specific data to communicate risk more effectively and motivate testing in the highest-risk neighborhoods.
  • Promote Testing at Point of Sale: As recommended in the TBDHU’s 2015 report, the City of Thunder Bay should strongly consider adopting a bylaw or policy that requires all new homes to be tested for radon prior to sale and encourages testing during all real estate transactions.³³
  • Support Financial Accessibility: All levels of government should explore programs to make radon testing and mitigation more financially accessible for low-income households, ensuring that financial constraints do not become a barrier to health and safety.³³