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Protecting Lake Ontario and the redside dace

The expansion of the Mid-Halton Wastewater Treatment Plant encompassed a range of sustainability measures.

Aerial shot of the facility


The Mid-Halton Wastewater Treatment Plant is located in Oakville, Ontario, part of the densely populated and rapidly growing Greater Toronto Area. In order to meet increased demand and continue to protect the water of Lake Ontario, it became necessary to increase the plant’s capacity from 75 million liters per day (MLD) to 125 MLD.

In addition to an upgrade of the plant’s headworks, a new outfall pipeline was needed — but the most direct route would cross 14 Mile Creek, which provides habitat for saw-whet and long-eared owls as well as the endangered Redside Dace, a small fish marked with red and yellow stripes that requires pools and slow-flowing streams with overhanging grasses and shrubs.


Mott MacDonald recommended 65 measures to reduce the overall footprint of mechanical,
electrical and lighting design. High-efficiency equipment was selected to reduce life cycle energy
costs. Design and selection of high efficiency blower units for the activated sludge train achieved
significant reduction in energy demand and thus long term operating costs.

Other sustainability opportunities identified included solar generation of site electricity, cogeneration of energy (electricity and heat recovery) from biogas, and heat energy recovery from sanitary effluent. Microhydro generation from the outfall was added into the plant’s final design.

Improvements to the stormwater system included expansion of the existing stormwater pond, addition of low impact development measures throughout the site, and an additional pond featuring low flow wetlands and subterranean overflow galleries. The existing pond discharge had a cooling trench feature added to reduce the temperature gain of the permanent pool. For every tree removed, three trees were planted.


The upgrade to the Mid-Halton Wastewater Treatment Plant will ensure that the needs of the area are met for the foreseeable future, while protecting the water of Lake Ontario.

Mott MacDonald demonstrated that our design and proposed construction methods would allow an alignment that crossed 14 Mile Creek while protecting the specialized habitat of the Redside Dace.

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