Relocating the Dufferin Sanitary Trunk Sewer from under the G. Ross Lord Reservoir

Abstract

Inflow and infiltration (I&I) are a common problem faced by municipalities regarding their gravity sewer collection systems, as well as the burden the additional flow has on downstream treatment facilities. I&I is typically from groundwater around the pipe, but for the Dufferin Sanitary Trunk Sewer (STS), the G. Ross Lord Reservoir is located directly above the STS with a storage capacity of 5,000,000 m3 . The reservoir is north of Finch Avenue and west of Dufferin Street, major thoroughfares in Toronto, and is fed by the Don River. The existing Dufferin STS itself runs along the west bank of the river, under the reservoir and earthen dam, eastward where it connects to the West Don STS. In 2010/11, the Dufferin STS was inspected, and active degradation was noted with significant I&I issues under the existing surface watercourse and the reservoir. The preferred approach to address the deterioration and significant I&I was a combination of realignment using HDPE lined, 1,200 mm diameter reinforced concrete jacking pipe microtunnel around the reservoir and dam, and CIPP lining of the STS sections to remain-in-service outside the reservoir footprint. Construction for this work started in 2023 and was substantially completed in the summer of 2025. This paper will discuss the design and construction of the project, including challenges encountered during construction associated with deep shafts (up to 22 m in depth) located in a highly permeable formation beneath the groundwater table, challenging surface conditions, traffic management, and climate change, and how these challenges were addressed by the contractor and design team.