Originally built in 1925, the St. Thomas Water Pollution Control Plant has been upgraded and expanded several times. The plant currently has an average rated capacity of 27,300 cubic metres per day.
In 2012, the City of St. Thomas retained Associated Engineering to complete a structural condition assessment of the three digesters and prepare preliminary design documents and cost estimates for the rehabilitation of the digesters. We discovered the tank of Digester No. 2 required significant structural repairs to the concrete roof in order to pass the pressure testing requirements. We advised the City that similar structural issues would likely be uncovered in the remaining digesters. Due to the high structural repair costs required for the roof of Digester No. 2, we recommended to forego the work on Digesters No. 1 and No. 3.
Associated Engineering recently completed a Digester Planning and Implementation Study. The goal of this study was to determine upgrade options, including life cycle costs, that would address both short-term and long-term needs of the anaerobic digestion system. Geotechnical and preliminary hydrogeological investigations have revealed some challenging areas with poor soils and requirement for dewatering. The impact of these conditions were included in the cost estimates to ensure the City allocates appropriate funds and contingencies.