River Channel Risk Management Design and Construction Support
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The Port Lands Flood Protection and Enabling Infrastructure Project (PLFP) is a major brownfield redevelopment project in Toronto, Ontario, Canada, consisting of over 715 acres of waterfront land around Lake Ontario. The former industrial area with soil and groundwater contamination issues is being redeveloped into major park lands and mixed-use development.

This scope of work includes the excavation of a new outlet river channel connecting the Don River to Lake Ontario, to alleviate upstream flooding and provide new wetlands and park assets for the City of Toronto.  The primary objectives of the river channel design are to i) provide long-term environmental protection of surface water, future visitors, workers, and ecosystem components ii) limit the inflow of groundwater into the river channel to allow for the construction of the  overlying revetments, slopes, and river finishes under dry conditions, iii) develop a design that can be integrated with other aspects of the Port Lands redevelopment including, but not limited to, civil construction, utilities, earthworks and soil reuse, river finishes, and parks.

Geosyntec's Scope of Services

Geosyntec's initial scope of work was with Michael Van Valkenburgh's (MVVA) client, Waterfront Toronto, to provide a third party technical review of the long-term environmental risk management measures (RMMs) associated with the river channel and designed to address mobile non-aqueous phase liquid (NAPL), residual NAPL, and dissolved phase NAPL. Geosyntec's peer review role then transitioned to the lead for the RMM river channel design for MVVA.  Geosyntec leads the structural and environmental design of a vertical cutoff wall and a horizontal barrier layer associated with the construction of the river channel RMMs. The vertical cutoff wall is a combination secant piles and slurry walls used to provide support-of-excavation for the removal of up to 22 feet of soil below the groundwater table, while also acting as hydraulic cut-off to limit groundwater infiltration into the excavation. The horizontal barrier consists of a geosynthetic clay liner (GCL), geomembrane, and granular activated carbon (GAC) reactive layer.

As part of the RMM design Geosyntec has i) developed construction drawings, specifications, and bid forms; ii) constructed a groundwater flow model to assess the potential impact of pre and post construction groundwater flow conditions; iii) performed site-specific NAPL sorption and isotherm testing to optimize design parameters and barrier material selection, iv) conducted seepage analysis to estimate dewatering rates and optimize cutoff wall depths; v) conducted geotechnical analysis to assess global and internal stability of the RMMs during and post construction, as well as shallow and deep foundation designs for supporting bridges; vi) developed an online information management system for the automated tracking and reporting of the RMM construction process; and vii) filled the role of resident site inspector for the installation of the secant piles.

Notable Accomplishments

Geosyntec's geotechnical design experience allowed for the incorporation of value engineering design practices that have led to cost optimizations.  Geosyntec's continued collaborative approach to the river channel design has facilitated a solid working relationship with MVVA, their client Waterfront Toronto, the site construction manager, and other design team consultants, allowing the continued early identification of design alternative optimizations and potential challenges, while meeting strict design deliverable deadlines for this game-changing project.

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Project Summary

  • Location: Toronto, Ontario, Canada
  • Client: Michael Van Valkenburgh Associates Inc.
  • Project Practice Areas: Waste Management, Water and Natural Resources
  • Type of Facility: Brownfield Redevelopment
  • Services Provided: Design basis for river channel environmental risk management measures; Design-build specifications, calculation packages, and issue for construction drawings for river channel construction RFP; Technical resident site inspector support for river channel risk management measure construction
  • Type of Work: River Channel Construction
  • Governing Regulation: National and Local