219991 - 2025-IS-11 - Spiragester Decommission and Cleaning

The Town of Ladysmith Waste Water Treatment Plant (WWTP) includes an aging concrete overflow holding tank originally constructed in 1965 as a “spiragester,” a structure used for combined sedimentation and digestion in earlier wastewater treatment systems. Over the decades, the tank’s role has evolved, and it now functions solely as an overflow holding facility. Several obsolete components remain in place from its previous use, most notably an internal steel baffle cone and an HDPE skirt, neither of which   serve any current operational purpose.

A 2023 condition assessment conducted by Associated Engineering identified the cone and skirt as being in very poor to fair condition, with signs of deformation, corrosion, and detachment. Their continued presence poses safety risks and complicates access to the tank interior for inspection or maintenance. Additionally, the cone protrudes through the central grated walkway, interrupting access and functionality.

This project aims to remove the redundant skirt, overflow weir and cone, clean the tank interior of residual debris and deterioration, and reinstate the walkway to restore safe and full access to the tank. These upgrades will support future maintenance activities, enhance safety, and improve operational efficiency at the facility.