The Foam Under the Tracks
What Alto hasn’t told you about the millions of cubic metres of plastic foam required to build high-speed rail through soft ground
- High-speed rail through soft ground requires enormous quantities of plastic foam — both as thermal insulation under the track and as lightweight structural fill over unstable soils. These materials have received no discussion in Alto’s public documents.
- The southern (Frontenac Arch) corridor would require an estimated 2.0 to 3.0 times more foam fill than the northern (Highway 7) corridor for the Peterborough–Ottawa segment, driven by greater exposure to Leda clay, wetlands, and karst terrain.
- This differential translates to an estimated $187–$269 million in additional construction cost on the southern route — before any accounting for environmental risk or future cleanup.
- Buried plastic foam leaches chemicals into groundwater over decades, including a potential human carcinogen and substances that harm aquatic life. The risk is substantially higher where foam sits over karst limestone that feeds drinking-water springs.
- At end of life, the foam must be dug up and disposed of — a liability estimated at $66–$113 million for the southern corridor alone. Some of this foam may legally qualify as hazardous waste.
- Alto has published no geotechnical comparison of the two corridors. The public cannot evaluate the routes without this information.
What is foam doing under a railway?
XPS — The frost shield
Extruded polystyrene (XPS) is a dense, rigid foam board — the same category of material as the pink or blue insulation boards used in building construction. In railway engineering, XPS boards are laid continuously under the entire length of the track to stop winter frost from penetrating the ground beneath. Without this layer, repeated freezing and thawing would heave and distort the track.
Frost in the Peterborough–Ottawa corridor can penetrate 1.2 to 1.8 metres into the ground in a cold winter. XPS keeps the subgrade above freezing. Both corridors need roughly equal amounts.
EPS Geofoam — The lightweight fill
Expanded polystyrene (EPS) geofoam is the lightweight foam used to build up embankments over soft, unstable ground. It looks like the white bead foam in packaging, but comes in large moulded blocks. At 15–30 kg per cubic metre, it weighs roughly 1 to 2% as much as conventional gravel fill.
This matters enormously over Leda clay — an unstable post-glacial soil found between Ottawa and the St. Lawrence — which cannot support the weight of conventional fill without sinking by 0.5 to 1.5 metres. EPS geofoam dramatically reduces this load. The southern corridor traverses far more Leda clay than the northern route, driving a massive difference in EPS quantities.
What is Leda clay?
Leda clay (also called quick clay or sensitive marine clay) is a post-glacial marine deposit laid down in the ancient Champlain Sea about 8,000–10,000 years ago. It is found throughout the Ottawa–St. Lawrence lowlands. When undisturbed it is weak but stable; when disturbed by construction loading or vibration, it can liquefy catastrophically. The 1971 Saint-Jean-Vianney landslide, which killed 31 people, was a Leda clay failure. High-speed rail cannot be built over it with conventional gravel embankments.
Why does the corridor choice matter so much?
The northern corridor (Highway 7 alignment) follows meta-sedimentary rock and competent till — geologically stable ground. Leda clay and wetland crossings are estimated at 10–15% of the route length, concentrated near Ottawa.
The southern corridor (Frontenac Arch) crosses Leda clay, organic wetland soils, and karst limestone across a much greater length — an estimated 25–30% of the route. This directly multiplies the foam quantities required, and the associated costs, carbon emissions, and long-term environmental liabilities.
The Two Corridors: A Geotechnical Comparison
The Peterborough–Ottawa segment spans approximately 270 kilometres through highly variable terrain. The two candidate corridors present fundamentally different ground conditions that drive divergent requirements for insulation and foam fill.
| Ground Condition | Northern Route (Hwy 7) | Southern Route (Frontenac Arch) |
|---|---|---|
| Dominant geology | Meta-sedimentary rock, competent till | Precambrian granite, karst limestone, Leda clay |
| Soft ground exposure | ~10–15% of route | ~25–30% of route |
| Leda clay sections | ~20–30 km (Ottawa approaches only) | ~40–60 km (Ottawa + South Nation valley) |
| Wetland / organic soil crossings | ~15–25 km | ~30–45 km |
| Karst / sinkhole risk | Low | Moderate to High |
| Average embankment height over soft ground | 3.0 m | 4.0 m |
XPS frost insulation — both corridors equal
XPS thermal insulation is required continuously along the full track length of either route, since both face the same Ontario climate. Quantities and costs are therefore approximately equal for both corridors.
EPS geofoam — dramatically different by corridor
EPS geofoam is where the corridors diverge sharply. The soft-ground length on the southern route is estimated at 2.4 to 2.9 times greater than on the northern route, and the deeper, wider embankments required over Leda clay and karst terrain compound this further.
| EPS Geofoam | Northern Route | Southern Route | Difference |
|---|---|---|---|
| Soft-ground length requiring EPS | 27,000–40,000 m | 65,000–80,000 m | +~2.4× southern |
| Average embankment fill depth | 3.0–3.5 m | 3.5–4.5 m | Deeper on south |
| Total EPS volume (mid-range) | ~1.3 million m³ | ~3.9 million m³ | +~2.6M m³ southern |
| EPS mass (mid-range) | ~26,520 tonnes | ~77,700 tonnes | +~51,000 tonnes south |
| EPS installed cost (mid-range) | ~$96 million | ~$283 million | +~$187M southern |
| Total foam materials cost (mid-range) | ~$125–$170M | ~$312–$439M | +$187–$269M southern |
The southern corridor is estimated to cost $187–$269 million more in foam materials alone for the Peterborough–Ottawa segment — a cost that does not appear in any Alto public document. This figure does not include the additional foundation measures that would also be required.
The Environmental Footprint
Plastic foam materials carry environmental costs across three phases of their life: manufacture, decades in the ground, and eventual decommissioning.
EPS and XPS are fossil-fuel derived materials. Their manufacture releases significant carbon, and older XPS products use blowing agents with global warming potentials 700–1,400 times that of CO₂.
Buried foam slowly releases chemicals into groundwater over decades, including styrene (a potential carcinogen) and flame-retardant additives that harm aquatic life.
Removal of buried foam is expensive and disruptive, generating microplastic debris and potentially triggering Leda clay instability. Some foam may qualify as hazardous waste.
Carbon emissions from manufacture
| Material | Mass (southern, mid) | CO₂ per kg | Estimated CO₂ |
|---|---|---|---|
| XPS insulation | ~5,670 t | ~3.0 kg CO₂/kg | ~17,010 t CO₂ |
| EPS geofoam — southern route | ~77,700 t | ~2.5 kg CO₂/kg | ~194,250 t CO₂ |
| EPS geofoam — northern route | ~26,520 t | ~2.5 kg CO₂/kg | ~66,300 t CO₂ |
| Total — southern route | — | — | ~211,260 t CO₂ |
| Total — northern route | — | — | ~83,310 t CO₂ |
Source: Inventory of Carbon and Energy (ICE) database v3.0, University of Bath; European Plastics in Buildings database.
The blowing agent problem
XPS foam boards are manufactured using blowing agents — gases that create the foam’s closed-cell structure. Many North American XPS products still use hydrofluorocarbons (HFCs) with global warming potentials of 700–1,400 times CO₂. Without contractual specifications requiring low-GWP alternatives, XPS procurement could carry embodied carbon 5–10 times higher than the estimates above.
What leaches from buried foam into groundwater
Styrene monomer
Styrene is classified as a possible human carcinogen by the International Agency for Research on Cancer (Group 2B). Canada’s freshwater quality guideline is set at 20 micrograms per litre. Karst terrain can move contaminated groundwater tens of kilometres from the source before it resurfaces at a spring or river.
Flame retardant chemicals
Until approximately 2015–2017, the standard flame retardant in EPS was hexabromocyclododecane (HBCD) — now listed as a Persistent Organic Pollutant under the Stockholm Convention and banned for most uses in Canada. HBCD and its replacement chemicals can leach from buried foam over decades, with endocrine-disrupting effects on fish and other aquatic organisms.
Why the southern corridor is at greater risk
The combination of larger EPS volumes, proximity to karst limestone conduits (which move contaminated water rapidly underground with no natural filtration), and the presence of federally threatened and endangered species in the Frontenac Arch Biosphere Reserve creates a materially higher risk profile on the southern route. Groundwater quality degradation in karst ecosystems could harm breeding and foraging habitat for the grey ratsnake (Threatened), Blanding’s turtle (Threatened), and the eastern spiny softshell (Threatened) — without triggering any visible surface disturbance.
The Hidden Liability: End of Life
EPS geofoam and XPS insulation boards are warranted for 50–75 years in buried applications. When infrastructure reaches end of life, all of the buried foam must be excavated and disposed of. This is a substantial, long-term public liability that does not appear in any Alto cost estimate.
Why removal is difficult
- Depth and access: Geofoam embankments over Leda clay sit 3–5 metres deep. Excavating them requires significant dewatering — which risks triggering the very Leda clay instability the foam was installed to avoid.
- Fragmentation during excavation: Mechanical excavators break up EPS into debris and microplastic-contaminated soil. Standard equipment cannot remove foam intact at this depth.
- Groundwater dewatering: Excavation in Leda clay or wetland zones requires pumping out groundwater, which can be contaminated with leachate and microplastic-laden water requiring treatment before discharge.
- XPS removal: XPS boards are typically bonded to the concrete track slab and require mechanical breaking — they cannot simply be lifted out.
Decommissioning cost estimates
| Decommissioning Item | Northern Route | Southern Route |
|---|---|---|
| EPS geofoam removal (mid-range volume) | ~$15–$34M | ~$58–$97M |
| XPS insulation removal | ~$8–$16M | ~$8–$16M |
| Soil remediation (leachate zones) | Low to medium | Medium to high |
| Total estimated decommissioning | $23–$50M | $66–$113M |
The HBCD hazardous waste risk
EPS manufactured before approximately 2015–2017 used HBCD as its standard flame retardant — now a banned persistent organic pollutant. After 50+ years in the ground in groundwater-influenced conditions, this foam could be classified as hazardous waste under Ontario Regulation 347 and the Canadian Environmental Protection Act, requiring controlled and significantly more expensive disposal.
The decommissioning liability for the southern corridor’s EPS geofoam alone is estimated at $66–$113 million. This long-term public cost does not appear in any Alto financial disclosure, any Infrastructure Canada funding application, or the McGill TRAM cost model. It would ultimately fall to the public to pay.
What Alto Has Not Disclosed
Alto’s public consultation materials contain no comparative geotechnical analysis of the foundation engineering requirements for alternative corridor alignments. The quantities, costs, environmental risks, and decommissioning liabilities associated with foam insulation and geofoam are nowhere addressed.
What is missing
- No geotechnical baseline study for either candidate corridor has been published — no borehole data, no characterization of Leda clay extent or depth, no wetland soil assessments.
- No lifecycle environmental assessment of polymer and synthetic materials has been included in any Alto environmental documentation.
- No decommissioning cost provisions for buried polymer materials appear in any published cost estimate or Infrastructure Canada funding documentation.
- No material specifications addressing HBCD prohibition or low-GWP blowing agent requirements have been publicly released.
- No corridor comparison applying equivalent technical standards to both the northern and southern routes exists in any public document.
Recommendations
- Alto should publish a geotechnical baseline study for both corridors, including borehole and cone penetration test data sufficient to characterize Leda clay extent, depth, and sensitivity, wetland soil depths, and karst void risk zones.
- The Environmental Impact Statement should include a lifecycle environmental assessment of all major polymer materials used in foundation construction.
- Alto’s project specifications should explicitly prohibit HBCD flame retardants and require low-GWP blowing agents in all XPS procurement.
- Decommissioning cost provisions for buried polymer materials should be included in the project’s financial disclosure as a long-term public liability.
- A Parliamentary Budget Officer review of Alto’s full lifecycle cost should include a line item for geotechnical material quantities and decommissioning.
How These Estimates Were Made
All quantity estimates are based on publicly available geotechnical and geological information for the Peterborough–Ottawa region, including Natural Resources Canada surficial geology mapping, Ontario Geological Survey open-file data, and published research on Leda clay distribution by the Geological Survey of Canada.
These estimates are not based on project-specific geotechnical investigation data, as none has been publicly released by Alto. They represent plausible ranges for planning and policy purposes and should be treated as order-of-magnitude indicators. This document has been prepared by citizen researchers and has not been peer-reviewed. It does not constitute engineering advice.