Porirua Sewage Tank Costs Soar, Completion Still Ahead of Schedule

A new wastewater storage tank in Porirua City, New Zealand, is now projected to cost $99 million, more than double its initial $48 million budget from 2022. Despite the significant cost increase, the project is currently on track for completion in April, three months ahead of the original schedule.

Project Details and Cost Overruns

The tank, designed to hold the equivalent of three Olympic swimming pools of wastewater, is located between State Highway 59 and the rail lines. The initial budget was established when construction began in 2022. Several factors contributed to the cost escalation, including the need to relocate native skinks, inflation, the discovery and relocation of fibre ducts, and upgrades to existing wastewater infrastructure.

Skink Relocation Efforts

The presence of northern grass skinks caused months of delays to the earthworks phase of the project. Between September and October 2023, workers captured 59 skinks using specialized traps and by hand, relocating them to a newly fenced-off habitat. Each skink was individually weighed, measured, and photographed during the process. The surrounding area of the tank will be planted with skink-friendly vegetation, including coprosmas, hebes, flaxes, and vines.

Wellington Water Response and Future Updates

Wellington Water is managing the project in collaboration with Capital Journeys and CPB HEB. A Wellington Water spokesperson indicated that a detailed briefing on the cost increases would be provided to the Porirua City Council on March 19th. The spokesperson also stated that the project remains ahead of schedule and, upon completion, will significantly reduce the risk of wastewater overflows into the environment.

Current Project Status

As of late December, the tank’s pump station had been commissioned using fresh water, and the installation of interconnecting pipework was expected to be finished in late February.

Further details will be discussed at the upcoming council workshop with Wellington Water chief executive Pat Dogherty.