Canadian Consulting Engineer
Toronto hopes for big benefits from soil recyclingEnvironmental Environment
To anyone else it just looks like a pile of mud, but to David DuBois, P.Eng., executive director of geo-enviro...
To anyone else it just looks like a pile of mud, but to David DuBois, P.Eng., executive director of geo-environmental services with Waterfront Toronto, it has a story. Just by looking at the pile, he says, he knows the soil is contaminated. It is lumpy and black, and certainly ugly.
A few hundred yards away, beside one of the two pilot soil recycling plants that are operating south of Lakeshore Boulevard, are neat stacks of sorted material. One is a pile of large boulders and worn-down blocks of concrete and brick. Another pile almost looks like coal, and another consists of clean washed pebbles that you could almost imagine on a rugged beach. This kind of salvaged material could — if the economics are right and the environmental authorities approve — be reused for foundations and other works in the vast new developments that are planned for the waterfront area.
As is the case with many cities in Canada, Toronto’s waterfront has an industrial past — leaving a legacy of contamination. The contamination consists mostly of three types, explains DuBois — petrochemicals, metals, and the by-products of burning.
During the soil recycling process, the soils are graded and separated according to size using water and mechanical means. The contaminants adhere to the smaller silt and clay particles, which the machines expel at the end of the process as a thick, dark slurry. At a distance across mud-soaked yards is a large lagoon that has been specially constructed to catch run-off water from the plants and in turn return it back to operate the machinery, in a closed-loop water system.
The contaminated material, as well as any hazardous material, will be taken off site. Nonetheless, DuBois says that with the recycling technologies about 70% of in-situ soils along the waterfront could be cleaned and reused.
The two pilot recycling plants are located in the sprawling Port Lands, the most southeasterly of the several parcels that make up the Waterfront Toronto revitalization project. This is the largest brownfield redevelopment in North America. The entire 800-hectare site stretches from Bathurst Street in the west to the Don River mouth in the east.
The soil recycling pilot plants rumbled to life in September and are about half-way through their tests. By the end they will each have processed around 10,000 cubic metres of material, but only one will be selected for the massive job over the next decade of recycling over 2 million cubic metres of soils across the entire waterfront lands. Besides the soil grading and washing process, both pilot projects are doing supplemental studies on remediation technologies such as biological and thermal treatments.
As we walk over to one of the plants, David Kusturin, vice president of program management with Waterfront Toronto, explains that the benefits from an environmental point of view soil recycling are twofold. First it saves having to haul the material off site and it saves filling landfills. Second it means that they can reuse the recycled material in the construction sites that will be proliferating along this shoreline over the next decades. Using materials ready to hand has huge environmental savings in fewer truck trips and less need to quarry for materials.
Waterfront Toronto held a request for proposals from different soil treatment companies last year, and selected two for the pilot. One of the two plants is owned and operated by DEC, a Belgian company that has partnered with local consultants Coffey Geotechnics. This system was used to clean up lands for the 2012 Olympics in London, U.K. The other plant is operated by Tetra Tech Construction Canada with a Dutch-owned company Stuyvesant Environmental Contracting.
Environ of Mississauga is overseeing the project on behalf of Waterfront Toronto.
The pilot project will help Waterfront Toronto to identify the different options for treating the soil, and to weigh up their costs and their various benefits. Success also depends, of course, on making sure that the soils can be cleaned up to the Ministry of Environment standards.