The work has been budgeted to cost about $140 million and the Dunedin City Council is calling for proposals.
Initially, the focus would be on a water treatment plant upgrade at Waikouaiti and wastewater treatment plant upgrades at Mosgiel, Green Island and Tahuna.
Work is also needed at other water treatment plants, such as setting up for fluoridation at Port Chalmers and Outram, replacing filtering systems and improving instrumentation.
Initial work for wastewater projects has been estimated at about $25 million and the initial cost for the water projects would be about $15 million.
Most of the council’s $140 million budget has been allocated to 2025-31.
An upgrade of the Waikouaiti water treatment plant has been signalled for some time and attention was drawn to it in the aftermath of last year’s lead contamination scare.
The council has said the upgrade would include treatment to improve taste and odour issues.
The upgrade will include two new treated water reservoirs, new wastewater settling ponds and a new backwash discharge pipeline.
Work at the intake will also be needed, such as installation of new raw water pumps, sump pumps and air-burst cleaning equipment.
The council has said in tender documents the purpose of the upgrade is to deal with issues with drinking water compliance, and to improve treated water quality, resilience and operation of the plant.
Beca has completed a concept-level design for the water treatment plant upgrade.
The wastewater treatment plant at Mosgiel is to have a new sludge tank and a new gas flare-burner system.
Screens will be replaced at Tahuna and electrical upgrades may be needed for an ultraviolet treatment system at Green Island.
The council has indicated two different contractors may lead the water and wastewater work, but it is possible one firm may lead both.
The deadline for proposals is November 30 and contracts could be awarded in December or January.
