Senior Environmental Engineer, P.Eng, QP(ESA)
Senior Environmental Engineer
As cities around the world become more densely populated, they sprout fast-growing forests of gleaming residential towers. But before those towers go up, builders must first excavate soil to create basements for storage and parking facilities.
A typical condo tower starts with an excavation of 30 metres by 30 metres that is 12 metres deep. That is about 10,000 cubic metres of excess soil, or roughly 20,000 tonnes. Multiply that by five condos a year in small cities, and it can add up fast – generating approximately 100,000 tons of excess soil per year, for just one city.
There’s increasing public and regulatory concern about how that excess construction soil is used, and legislators in Ontario and around the world are taking action. We see this in places as diverse as Australia’s State of Victoria (the Environmental Protection Amendment Act 2018) and Canada’s Province of Ontario (Ontario Regulation 406/19), where new legislation seeks to provide better outcomes for excess soil from construction sites.
Here are some of the trends we are seeing…
Conserve landfill space by diverting excess soil
Partly because of uncertainty around disposal of excess soil, many developers find themselves paying landfill tipping fees to dispose of their excess soil. However, many landfills are nearing capacity and it can be very difficult to get a permit to expand a landfill or open a new one. So, landfill operators are increasingly reluctant to use scarce permitted capacity for excess soil.
Also, it is becoming clear that soil is a precious, finite commodity that takes Mother Nature many years to produce, and so it must be conserved. As a result, putting excess soil into a landfill is now increasingly seen as a last resort. It’s not a waste product to be disposed of, but rather a resource to be cared for and used wisely.
Make me a match: finding beneficial uses for excess soil
If landfills are no longer welcoming excess soil, builders must find other ways to dispose of it. The answer lies in the adage, “One person’s trash is another’s treasure.” What may be excess soil in one place may be welcomed as necessary fill in another – perhaps to bring a site up to grade. The key lies in matchmaking and connecting the two parties so they can meet each other’s needs.
Golder recently played a role in making a connection between two projects in Ottawa, Canada. One project was a tunnel under the central core of Ottawa, being dug for a light-rail line for the municipal transit authority, OC Transpo.This project had generated a large volume of cuttings that needed disposal. The other project was a housing development in Ottawa called Greystone Village, which needed to backfill a remedial excavation and to construct engineered fill pads for support of low-rise residential foundations.
One of the contractors bidding on the housing project noted the need of the tunneling project to dispose of its tunnel cuttings. At the contractor’s request, Golder tested the cuttings and determined that they were fit for the purpose on the housing project site. Being able to connect these two needs — “I have excess soil and you need fill” — for the benefit of both parties, will become an increasingly valuable skill in the years ahead.
Finding a good outcome for excess soil, early in planning stages
Until recently, in many places, the topic of excess soil was not high on the priority list for developers. They were much more concerned with structural issues of the building itself. But the State of Victoria’s legislation is one example of putting a higher priority on finding responsible outcomes for excess soil. Ontario’s new legislation has similar intent in that it makes clear that unless a plan is developed and approved for soil reuse or disposal, it will be difficult for excavation to begin.
Soil banks and soil processing: interim storage makes planning easier
The need to find a good home for excavated soil – a use that is appropriate for the soil type and meets regulations – has the potential to cause project delays. Ontario has taken steps towards providing relief by allowing for the temporary storage of excavated soil. This comes in the form of “soil banks,” as well as soil processing facilities, which are new aspects of the guidelines in the province.
Data management makes it all work together
There is likely to be a growing need for skills and tools to demonstrate that excess soil is being managed appropriately. For example in Ontario, if a truck leaves a construction site with a load of excess soil, there must be a clear destination in mind – and that destination must have agreed, in writing, to take soil of the quality and type that is in the truck. Trucks will be inspected to make sure that the spirit and the letter of the regulations are being followed.
This will create demand for data management tools to track loads leaving the site and the load’s specifics, like its destination, the record of acceptance by the receiving site, and the load’s delivery date. Developing a soil management plan and tracking system to reduce costs and risk while improving environmental conditions is key.
Understanding excess soil and how it can affect the feasibility of your project is challenging and necessary. Protecting the natural environment and human population from any potential soil-based hazards, while also diverting excess soil from landfills and handling it like a valuable and viable resource is the key to delivering better outcomes.