Waterfront Toronto is constructing an innovative stormwater treatment and conveyance system to service the West Don Lands community and future development in the North Keating portion of the Lower Don Lands. The system will feature a new purpose built plant that will utilize the latest technology to treat stormwater.

West Don Lands and North Keating are located within the floodplain of the Don River and flood mitigation and stormwater management are critical issues that need to be addressed as part of revitalization.

As a former industrial area, the West Don Lands lacks appropriate stormwater infrastructure to support the influx of new residents that redevelopment will bring. Plus, construction of the area’s flood protection land form has rerouted stormwater flows away from the Don River, which previously received the bulk of the area’s stormwater.

Managing and treating stormwater – created by rain and melting snow – is critical to safely convey runoff, prevent flooding, and to ensure pollutants in the water are removed prior to the water being discharged into Lake Ontario.

The new system for the West Don Lands is an innovative approach to managing stormwater in the area. The state-of-the-art design addresses a number of constraints posed by its location within a dense, downtown urban setting and the use of the selected technologies in the multi-step treatment system is the first of its kind in Canada.

The innovative treatment system will achieve the stormwater treatment guidelines set out by the City of Toronto, as well as Waterfront Toronto’s broader commitment to protecting and enhancing the natural environment.

The system consists of a treatment plant, an oil grit separator, a series of strategically located underground shafts and tunnels, and a discharge outfall at the Keating Channel. Once captured, the stormwater will undergo several stages of treatment before being discharged into Lake Ontario.

The system was planned to maximize the extremely tight footprint of the site and reduce the need for above ground space for the plant equipment; and, at the same time to minimize the environmental effects and associated soil remediation efforts of construction.

The West Don Lands system will treat only stormwater, as opposed to treating combined sewer systems with stormwater overflows. Another unique feature of the system is the plant will use a combination of several adapted technologies as well as the main shaft as part of the treatment process.

The tunnel portion of the system was constructed by boring through bedrock deep beneath the soil, which minimizes intrusion in the area. Unlike traditional systems that fill in the shaft following construction, the West Don Lands system will reuse the tunnel construction shaft, built to launch the tunnel boring machine, as a storage facility to decrease flows to the stormwater treatment facility. This unique approach reduced the overall size of the system, thereby reducing both the cost to construct it and maintain it.

In the first stage of treatment, stormwater is collected and conveyed to a hydro dynamic oil grit separator located on the east side of Cherry Street, just north of the rail line. The oil grit separator removes sediment, screens debris and separates oil from the stormwater. After leaving the oil grit separator, the stormwater is conveyed to a storage chamber to await the second stage of treatment.

The second stage removes any fine suspended solids not captured by the oil grit separator using ballasted flocculation. Ballasted flocculation is a process that introduces a substance that binds the material together to make it heavier. The weighted material then sinks to the bottom of the chamber where it is isolated from the clarified water. The treated water is then conveyed to the third and final stage of treatment where it is treated using ultraviolet (UV) disinfection.

In the final stage of treatment, UV disinfection uses radiation from UV light to disrupt any organisms/bacteria in the water to deactivate or prevent them from reproducing. Following UV disinfection, the treated water is discharged into Lake Ontario at the Keating Channel.

The 300-square-metre treatment plant facility that is being built at the northeast corner of Lake Shore Boulevard and Cherry Street is intended to be a landmark structure for the West Don Lands. gh3, the architecture team, had to address the challenges of the site. The facility’s use and the project’s modest budget but still meet Waterfront Toronto’s requirements for design excellence. Their approach was to design a simple elegant building that brings a modern interpretation to the ancient story of water. The design of the facility enclosure comes from the idea of a stone well, inverted to be displayed as a sculptural form above ground. The building will be embellished by etchings on its surface that act as a system of

rain channels running from roof to wall, to ground plane and shaft that represent the broader system of urban hydrology in which the structure is rooted.

The faceted, limestone–clad building will be surrounded by the same material, creating a composition that will be a striking counterpoint to the infrastructural complexity around it. Strategically placed glazed openings will be set within the facade to reveal glimpses of the building’s inner workings and become glowing highlights at night. While interior and exterior LED lighting will abstractly register information about the building’s performance to transparently and compellingly convey the workings of civil infrastructure sustaining a city for its inhabitants.

The building was honoured with a 2011 Award of Excellence by Canadian Architect magazine. One of only two national award programs devoted exclusively to architecture, the Awards of Excellence have recognized significant building projects in Canada on an annual basis since 1968. The awards honour buildings in the design stage. Jurors considered response to the building program, site, geographical and social context and evaluated physical organization, structure, materials and environmental features.

The treatment plant construction will begin in summer 2012 and is expected to be completed in 2013.