Outfall Repair Project at Annacis Island Wastewater Treatment Plant

Metro Vancouver
Delta, BC

The project consisted of exploratory work to confirm the condition of existing outfall piping as part of Metro Vancouver’s efforts to facilitate long term maintenance, planning, and design. Emergency repairs were also required upon observed condition of the existing outfall.

Part of the work zone was inside the main navigation channel of the Fraser River so marine equipment needed to be staged to minimize interference with marine traffic. It also needed to be moved outside of the navigation channel when work was not actively being undertaken or when the crew was not on site.

Rainfall and strong currents limited the diving time so co-ordination and organization of crew was critical to maximize productivity during available dive windows. Additionally, poor visibility hindered divers’ ability to see equipment or loads in the water. GPS locators on divers and equipment allowed dive coordinators and equipment operators to see the live locations of divers and equipment and ensure diver safety while working near buckets and live loads.

Given the active river bottom conditions, sediment infill flows would have impeded normal diver controlled excavation procedures. As such, a crane supported “air lift” was used enabling the removal of sediments quickly and without damaging the existing outfall components. This also facilitated the time required for the dive crew to make the required repairs to the outfall. 

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