St Marys mine – Article Index

A proposal to excavate hundreds of millions of tonnes of limestone from beneath Lake Ontario raises many questions, starting with a big one: should we be planning for the continued expansion of the concrete industry, given what we already know about climate change?

St Marys Cement, a Canadian branch of Brazilian multinational Votorantim Cimentos, operates a limestone quarry and cement factory on the shore of Lake Ontario at Bowmanville, Ontario. The company wants to expand by tunnelling under Lake Ontario from the existing quarry, and removing up to 4 million tonnes of limestone a year for the next 100 years. (The Project Description for the expansion is here.)

Graphic from St Marys Project Description

(A note on terminology: in this article I use “cement” to refer to the white powder that is mixed with gravel and water, and “concrete” to refer to the construction material that results when the gravel-cement mixture reacts with water and solidifies.)

While concrete is one of the most important and ubiquitous materials in modern life, the cement industry is a major source of greenhouse gas emissions, accounting for 8% of global carbon emissions (Macleans, 7 March 2016). The emissions occur because when limestone is cooked to transform it into cement its natural carbon content is released, and because it takes prodigious amounts of heat to effect this chemical transformation. That is why the St Marys plant in Bowmanville burns both coal and bitcoke (the black powder left over from bitumen after refining) by the shipload.

Not only is cement production carbon-emissions intensive, but the way we use cement tends to encourage further carbon emissions. The biggest share of cement in Ontario goes into concrete pavement which is used to widen roads and add new parking lots – which in turn promotes greater use of cars and trucks.

Which brings us back to the St Marys expansion plan. The company is not saying it will expand its cement production in Bowmanville, but the additional limestone will most likely be used with cement. For further clarity, the limestone extracted from under Lake Ontario will be marketed in industry parlance as “aggregate” – what most people refer to as gravel. And that aggregate will mostly be mixed with cement, to form concrete, or used as a base layer underneath slabs of concrete. In other words, the quarrying of limestone for aggregate will complement St Marys core business of quarrying limestone for cement.

Is a major new source of aggregate needed in the Toronto area? St Marys says in their Project Description:

Over the past 20 years, Ontario has consumed over 3 billion tonnes of aggregate and limestone or about 164 million tonnes per year on average. Given expected levels of economic and population growth, Ontario’s consumption of aggregates and limestone for cement is projected to average about 186 million tonnes per year over the next 20 years.” (Project Description, page 8) [emphasis mine]

The key phrase here is “given expected levels of economic and population growth”. If the economic trends of the past 20 years continue on the same track for the next 20 years, aggregate use will go up by 13 per cent – from 164 million tonnes per year to 186 million. In other words, if we continue Business As Usual, we will need more aggregate.

How is this aggregate used?

Aggregate and limestone are used for a wide range of applications in Ontario; however, the primary use is in construction work, either directly on construction sites, or in the manufacturing of concrete and other building products. Roads (provincial highways, as well as municipal and private roads) account for the largest share of aggregate used in construction work.” (Project Description, page 8) [emphasis mine]

In recent decades the area of pavement has grown faster than the population has grown, because urban sprawl has been the dominant form of development. If we project that “Business As Usual” scenario into the next generation, we’ll need to build a lot more roadway, we’ll need a lot more aggregate, and we’ll need a lot more cement.

But the “Business As Usual” scenario collides head-on with Canada’s official climate policy commitments. Although no one thinks we can or should stop using cement (or fossil fuels) tomorrow, it is clear that we should be making every effort to reduce our carbon emissions immediately, and reduce those emissions at a faster rate with each passing year. That means we should be planning to reduce, not increase, the role of car-dependent sprawl in our urban developments; reduce, not increase, the amount of new pavement we place atop our land each year; and reduce, not increase, the amount of cement we need to cook up and mix with aggregate for concrete each year.

The Business As Usual scenario means we don’t take seriously the climate science consensus that continued growth in carbon emissions will be catastrophic for our grandchildren, and we don’t take seriously our government’s commitment to an economy-wide reduction of emissions.

St Marys Cement notice of Public Information Centre, Monday December 5, 2016

Yet there is no evidence in the St Marys Project Description that anything other than a Business As Usual scenario is being considered. Regarding the carbon emissions of the project, the most substantive comment is that the quarry will have “reduced GHG [Green House Gas] emission intensity compared to other quarries that are located further from market.” The report does note, however, that “potential effects on climate change as a result of the Project will be characterized through the EA [Environmental Assessment] process.”

When this Environmental Assessment process gets underway, will St Marys be required to show that the expansion project is consistent with Ontario’s and Canada’s official climate policies? Stay tuned.

Top photo: The Peter Cresswell docked at the St Marys Cement port on Lake Ontario near Bowmanville.