Corrosion Control Strategies to Protect Linear Assets: Dundas Street Sanitary Sewer and Forcemain Project, Oakville in the Region of Halton, Ontario, Canada

Halton Region (the Region) is located west of the City of Toronto and is part of the Greater Toronto Area (GTA). It is one of the fastest growing municipalities in the GTA with the majority of the population residing in the following four urban areas: Oakville, Burlington, Milton, and Halton Hills. AECOM recently completed the Region's Sustainable Halton Master Plan that lays out sustainable growth and servicing strategies to meet the population and employment needs to the year 2031. As part of the Region's sustainable growth strategy, the Dundas Street corridor is key to developing the north end of the Town of Oakville. To facilitate this growth, AECOM designed the 1,000 L/s North Oakville Wastewater Pump Station (WWPS), twin 750 mm forcemains and 1,200 mm sanitary sewer, which was constructed in a 2,100 mm tunnel. This paper focuses on the corrosion reduction measures developed during the design phase of the project and implementation issues that occurred during construction. The 1,200 mm sanitary sewer and twin 750 mm forcemains carry sewage 2.6 km from the newly constructed North Oakville WWPS at Neyagawa Boulevard to Third Line on Dundas Street West. Design of the sanitary sewer and forcemains incorporates one cast-in-place manhole at Third Line and three precast manholes integrated as part of the tunnel shafts. The 450 m, 1,200 mm sanitary sewer was mostly constructed by tunnel methods. In addition to the sanitary sewer, twin 2.2 km, 750 mm diameter forcemains were constructed from the new North Oakville WWPS outletting into the new 1,200 mm diameter sanitary sewer on Dundas Street. The connection of the twin 750 mm forcemains to the 1,200 mm sanitary sewer was by two 7.1 m high drop structures (one for each forcemain). To reduce the release of odors and hydrogen sulfide (H2S), the project team investigated various design options that included several types of drop structures (e.g., vortex, baffle, vertical), various materials and coatings to resist concrete corrosion, and other site-specific options. Selection of the final drop structure design and construction materials was based on the team's previous large drop structure experience and input from various suppliers. The vortex drop structure was selected and designed to minimize maintenance and extend the life of the structure and downstream sewer. The design included the use of specialized concrete additives and coatings within the chambers in addition to a liner for the tunnel downstream of the chambers. The drop structure downstream pipe was protected from corrosion by T-Lock and Arrow-Lock. During construction, issues addressed included the adhesion of the specialized coating onto the chamber and release of the tunnel pipe liner at the interface between the tunnel and one of the chambers. The team worked with the suppliers and contractor to successfully resolve these issues.

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