Daily Commerical News & Construction Record, Dec. 20, 2011
Eastern Construction works on West Don Lands stormwater system for Waterfront Toronto
A $30-million project designed to control stormwater without disturbing the impacted soils in a former industrial area of east end Toronto is breaking ground both literally and figuratively.
DAN O’REILLY correspondent
When completed at the end of 2012, the West Don Lands Stormwater Quality Facility will treat and divert stormwater from the 32-hectare West Don Lands, which are currently being remediated so they can eventually be transformed into an approximately 6,000-unit mixed residential/commercial community.
Eastern Construction is the construction manager overseeing the project which comprised of three main components. They include a 95-square-metre, 12-metre-deep oil grit separator; a 3,000-square-foot treatment plant, and a 25-metre-deep, 300-metre long concrete-lined tunnel which will discharge treated stormwater into the Keating Channel, which is part of Lake Ontario.
The project got underway early in 2011 with the excavation of the tunnel through bedrock by Burlington-based C & M McNally Engineering Corp. With an average daily production average of 10 linear metres a day, the tunnelling is scheduled for a completion by the end of March.
When tunnelling operations are completed the new tunnel’s shaft will become an approximately 2,000-cubic-metre storage facility to manage flows to the new stormwater quality facility and then down the tunnel.
Dean Construction Company is the marine subcontractor building a coffer dam and dockwall for the outfall at the channel.
Shoring for the oil grit separator’s piping system is nearing completion. Construction of the separator will get underway early in January and will be followed by the construction start of the plant in June, says David Kusturin, vice-president of program management for Waterfront Toronto, the non-profit agency which is revitalizing the city’s waterfront.
The project partners, which include the agency, the City of Toronto, and consulting engineer R. V. Anderson Associates Ltd., are describing the system as the first of its kind in Canada. In part, that’s because the plant will specifically treat stormwater as opposed to combined sewer systems with storm water overflows. But that description is also being used because the plant will be using a combination of several adapted technologies and the main shaft as part of the treatment process.
Rather than filling in the shaft, as often occurs when tunnelling operations are complete, it will become an approximately 2,000-cubic-metre storage facility to manage flows to the plant and then down to the tunnel.
“We don’t need a lot of above ground space for the (plant) equipment,” says R. V. Anderson Associates project manager Peter Langan.
The need for the facility was first pinpointed in an environmental assessment conducted in 2005. One of its major proposals was that the stormwater be drained using primarily open construction, with a small tunnelling operation.
“We recommenced tunnelling the entire route,” says Langan, explaining R. V. Anderson was opposed to open cut construction for several reasons including the potential for major disruptions to the near GO train line and two major arteries, Lakeshore Road and the Gardiner Expressway.
There was also a very real possibility construction would have been hindered by docks, wharves and any other assortment of hidden obstacles buried there when that part of the city’s lakefront was landfilled decades ago, he points out.
Open cut construction would also greatly disturb the already impacted soils. With tunnelling only the shaft areas need to be remediated, says Langan.
The project is being carried out in accordance with Toronto’s Wet Weather Flow Management Policy which sets guidelines and identifies performances for controlling runoff from development sites, he says.
“Without this (the project) we wouldn’t be able to proceed with the development of the West Don lands,” says Waterfront Toronto’s David Kusturin.
But its importance extends beyond that immediate area. The facility will provide stormwater management for a large part of the city’s eastern downtown, west of the Don River, he points out.