Located east of downtown Toronto on the shore of Lake Ontario, the Ashbridges Bay Treatment Plant Outfall (ABTPO) project needed an upgrade.
The treatment plant is one of Canada’s largest and oldest wastewater treatment plants, built in 1910 and in operation since 1917. It is the largest of Toronto’s four sewage plants, with a peak hydraulic capacity of 3,300 megaliters of wastewater per day. However, the existing outfall had insufficient capacity for discharging treated effluent into the lake and was nearing the end of its service life, as it was constructed in 1947.
With team members in Canada, engineering company Hatch was responsible for the design and construction of a new tunneled outfall that would send treated wastewater from the treatment plant into Lake Ontario. The CAD$300 million (USD$230 million) project included sinking a shaft adjacent to the shoreline and then mining a tunnel through rock directly beneath the lake bed.
“To put the shaft and tunnel dimension into perspective, we’re effectively building a shaft which is a football field deep into the ground, a tunnel that is approximately three times the length of the Golden Gate Bridge, and a tunnel diameter that is the size of an average two-story house [for this project],” Kevin Waher, a senior project manager at Hatch said.
The treated effluent would then flow by gravity from the plant through connecting conduits to the shaft and tunnel out into the lake. The location, complexity, and scale of the project all presented major challenges.
Improving Wastewater Treatment for Toronto
The Hatch team realized early on that they needed software that combined computer-aided design (CAD) with engineering analysis to ensure the success of this project. Besides overcoming the multiple, complex challenges around the project’s construction, they also needed to minimize costs while considering the underwater soil and environmental features.
As the treatment plant services about 1.6 million residents in Toronto, the final result also needed to ensure an enhanced quality of life for the community, as well as any future residents as the city grows and expands.
The team determined that traditional engineering delivery methods would be insufficient for this project. In addition to the work surrounding the construction of the tunnel, Hatch also needed to build 50 vertical in-line diffuser risers to connect the top of the tunnel to the lake bed along the last 1,000 meters of the tunnel to help convey flows to the lake. Tunnel operations would have to be supported from the onshore shaft, while risers would be drilled from over-water barges.
Coordination would be key to ensuring the successful delivery of this project; and with the team scattered throughout various offices, they would need to develop digital collaboration workflows for efficient communication.
Software for Improved Engineering Analysis
The Hatch team was already familiar with Bentley Systems, having used their software during the project’s initial design phase in 2015. For this next phase of the project, they chose to use both Bentley’s OpenRoads and MicroStation as their design software, and ProjectWise software to enable and enhance collaboration.
The team used OpenRoads to map surfaces from borehole logs, including the lake’s water level and the anticipated tunnel invert. The software enabled the team to predict geological boundary conditions below the lake, which helped inform design decisions.
They discovered the most efficient depth of the shaft, mitigating potential risks of tunnel inundation from the lake. They created a circular profile around the shaft in OpenRoads to confirm soil conditions throughout, which helped determine the appropriate types of excavation.
With MicroStation, Hatch modeled all elements of the shaft and tunnel, allowing engineers to complete the tunnel rings and determine the proper rotation of each ring to help with possible connection problems. The platform’s 3D modeling provided a clear picture of the complex geometry, helping the engineering team prepare a simplified reinforcement plan.
They also modeled the excavation for the shaft, accounting for the depth of the structures, varying conditions of the soil and rock, and varying types of structures to ensure that their excavation plan would proceed on time and without any unforeseen delays.
Hatch also used Bentley’s ProjectWise connected data environment so that the team could collaborate across several time zones, ensuring that the project was delivered on time and under budget. They coordinated all CAD work, engineering analysis, and design in the platform, allowing the team to continue working on CAD drawings while PDFs were created on a separate server.
“Bentley’s suite of software was implemented on the ABTPO project to build practical solutions that solve unique engineering challenges, to facilitate a connected and collaborative work environment, and to deliver a cost-effective and efficient project,” said Waher.
Exceeding Client Expectations while Saving Significant Cost
For this project, Hatch delivered a high-quality design to their client ahead of schedule. The advanced CAD capabilities of OpenRoads and MicroStation allowed Hatch engineers to employ one full-time and two part-time team members, reducing staff hours by 2,000 hours and resulting in a CAD$350,000 (USD$275,000) savings.
With 3D models used for technical peer and constructability review workshops, 100 percent of tender submissions were delivered to the client a week in advance, saving CAD$25,000 (USD$19,000) in staff hour spend on CAD drawings. Also, because the project was paperless due to the use of ProjectWise’s connected data environment for sharing all documents and information, Hatch saved over CAD$35,000 (USD$27,000) in paper and printing costs.
These results were recognized by the client.
“The outfall design phase was completed to the city’s satisfaction, on time and under budget, which is commendable,” Justyna Teper, the City of Toronto’s outfall project manager said.
The new outfall is a critical element of the city’s improvements to the plant’s hydraulic capacity, and it is anticipated that the ABTPO project will help improve the city’s shoreline and beaches, as well as Lake Ontario’s water quality. WW
Published in WaterWorld magazine, March 2022.
