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Clean water and continued growth in Ontario

The new trunk sewer will provide critical backup for the existing sewer system, and increased capacity that will enable continued growth in the York and Durham Regions — without the need to build new treatment plants.

It is a large relief to get it done. It's the next 30 years of growth in York Region.

Bill Fisch

Chairperson, York Region

Southeast Collector Trunk Sewer

Southeast Collector Trunk Sewer


In 1965, the province of Ontario decided that no more sewage treatment plants should be built on the Humber, Don, and Rouge Rivers. In response, the Ministry of the Environment constructed a centralized, environmentally friendly system called the York Durham Sewage System (YDSS).

The YDSS, whose ownership was later transferred to the York and Durham Regions, uses modern sewers that keep sewage and stormwater in separate systems. Sewage from the two regions is carried via trunk sewer to the Duffin Creek Water Pollution Control Plant in Pickering. Treated effluent is discharged into Lake Ontario.

Existing pipelines in the YDSS were expected to reach their capacity by 2010. Fears that strains on the system could cause sewage to back up from the Yonge Street line caused a “virtual development freeze” in Richmond Hill from 2004 to 2006.

As part of Ontario’s Growth Plan for the Greater Golden Horseshoe, a project for a new Southeast Collector Trunk Sewer was approved. The Southeast Collector alignment runs for 15 kilometers (9 miles) through the City of Markham and the City of Pickering. The design includes 17 access shafts between 4 and 48 meters deep (13 to 157 feet) and diameters ranging from 4 to 14 meters (13 to 46 feet).

The project was the first in Ontario to undergo the rigorous Independent Environmental Assessment. The Assessment examined the environmental issues to ensure that the design approach would address meet Ontario requirements to “determine the ecological, cultural, economic and social impact of the project.”


HMM, a joint venture of Mott MacDonald and Hatch, provided project management and design services for the Southeast Collector Trunk Sewer, in addition to construction management services. The project was featured as one of Canada's Top 5 Water Projects in the January/February 2014 issue of Water Canada. The estimated project cost is about CDN $546 million.

The magazine quoted HMM’s Robert Kerrigan as saying odor management was a major challenge on the project. Kerrigan said the project includes 15 access sites along its alignment, including several that could have an impact on residential areas.

The design team addressed the community opposition to the project, including concerns about odor problems. An innovative large fan system will address odor issues by conveying air in an opposite direction to the flow of wastewater. Odors will be treated at an Odor Control Facility that is housed in a building under negative pressure and equipped with biofilter technology and activated carbon filters.

Our design services included the following:

  • Tunnel design support for the Individual Environmental Assessment
  • Design for a tunnel with a diameter of three meters (10 feet) to be excavated by four tunnel boring machines (TBMs) and lined with precast concrete segments
  • Design of 13 shafts, a connecting chamber to the existing YDSS, and several hand-mined tunnels between shafts

The joint venture provided the following contract-related services:

  • Procurement and contract management for supply and delivery of the TBMs and precast concrete linings
  • Preparation of contract documents and administration for advanced contracts for initial archeological investigations, utility relocations, and haul road upgrades
  • Preparation of documents for prequalification of contractors
  • Preparation of prime construction contract documents, addenda during the tendering period, bid analysis, and conforming of contract documents prior to award

Construction management services included the following:

  • Development of capital cost estimates and construction schedules
  • Administration of construction schedule, integrating the contractor, subcontractors, consultant, and owner in a single P6 enterprise database
  • Risk management, contractor schedule evaluation, cost control, field accounting, material quality assurance, and settlement surveying along the alignment
  • Involvement in Disputes Review Board hearings, and resolution of contractor claims
  • Management of TBM manufacturer during construction to facilitate maintenance, repair and supply of parts


The new trunk sewer will provide critical backup for the existing sewer system, and increased capacity that will enable continued growth in the York and Durham Regions — without the need to build new treatment plants.

Speaking when funding for the Southeast Collector was approved, York Region chairperson Bill Fisch said, “It is a large relief to get it done. It’s the next 30 years of growth in York Region.”

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