These floods are a sign that Oakville’s aging infrastructure is unable to manage surges in wastewater flow caused by the effects of combined flows and intense summer storms. This is a significant problem that will become worse in the future: A 2011 Canadian environmental roundtable concluded that a sharp increase in extreme storm events is inevitable, causing a predicted national cost of up to $17 billion a year by 2050.
Cole Engineering has been developing and designing a massive wastewater infrastructure revitalization plan since 2012, and the long-awaited operation began construction in summer 2015. Headed by project leader Troy Bauman, the Rebecca Trunk Wastewater Project has faced some difficult challenges and found some innovative solutions for Oakville’s unique infrastructure and ecosystem.
Project OverviewFour kilometers of microtunnel and one kilometer of “open cut” (accessed from the surface) construction will improve the Rebecca Trunk Wastewater Main from Trafalgar Road to the Oakville Southwest Wastewater Treatment Plant. With fourteen drives up to 400m long, with curved and composite-curved alignments, in rock and mixed-face conditions, it is one of the most interesting and challenging microtunnel projects planned in North America.
Environmental ConsiderationsWorking closely with the Ministry of Natural Resources and Forestry and Halton Conservation has allowed COLE to have a positive impact on Oakville’s vibrant habitat, including the home of the endangered Redside Dace in Fourteen Mile Creek. These small minnows (which eat flies by leaping from the water) benefit the creek by transferring nutrients from the air into the water and are an excellent indicator of an ecosystem’s health, since they are incredibly sensitive to environmental disturbances.
In addition to an innovative pre-engineered solution to allow the microtunnel to cross Fourteen Mile Creek unhindered, additional stream improvements will be completed upstream from the project site to provide an overall environmental benefit to the ecosystem.
Design FeaturesOne of the greatest challenges COLE had to address was the transition from the Rebecca Street bridge to the microtunnel (about 4m deeper) while maintaining the existing trunk sewer for operational reasons. The solution is a large, cast-in-place concrete chamber with integrated valves and controls, and a custom-designed vortex funnel. The whole chamber will be plastic-coated to protect against corrosion.
Bauman credits the mobility of a smaller firm like COLE for the project’s technical innovations, as the team is able to respond quickly and creatively to challenges like those encountered in this project.