A survey of the Tauranga Harbour floor between Katikati and Matakana Island is underway as Western Bay of Plenty District Council investigates long-term options for managing treated wastewater from Katikati.

During the next two weeks, specialist contractors will assess ground conditions beneath the harbour as part of investigations for the design and construction of a potential replacement of the existing pipeline across the harbour, one of the future wastewater disposal options being explored for the area.

In a statement, the council said the work was part of its Katikati Wastewater Disposal Future Directions project – a collaborative effort, guided by a project control group and Te Ohu Waiora, a group consisting of representatives from tāngata whenua, the council and external stakeholders.

The council’s director of water services Coral-Lee Ertel said the investigations were an important step in planning for the future.

“We’re focused on implementing a sustainable, long-term and culturally acceptable solution that protects our harbour, meets new wastewater standards and reflects the values of our community and tangata whenua,” Ertel said.

The Katikati Wastewater Treatment Plant discharges treated wastewater through an ocean outfall pipeline that extends across Tauranga Harbour, through Matakana Island, and out to sea.

A map of the treated wastewater ocean outfall pipeline that extends across Tauranga Harbour. Photo / Supplied

The ageing pipeline within the harbour had experienced several breaks during the past year, which highlighted the need for a long-term replacement strategy, the council said.

The plant’s discharge consent would expire in 2038 and the council said it was required to confirm its preferred future direction by the end of this year.

Following the completion of the Future Directions Report in 2025, the preferred long-term approach was retention of an ocean discharge, but with higher treatment standards and a longer outfall pipe.

The council also identified the early replacement of the ageing harbour crossing section of the outfall pipeline as a priority project.

The harbour floor investigations related specifically to the option of replacing the harbour crossing section of the pipeline.

The information gathered through the survey would help determine whether ground conditions were suitable for installing a replacement pipeline, support design of a replacement pipeline and would inform future resource consent applications for the works.

After a procurement process, Brown Bros Drilling was selected by the council as the most suitable specialist contractor to carry out the survey.

The survey comprises 14 investigation sites located along the proposed replacement pipeline route, which is just to the north of the existing pipeline location.

At each site, the crews would collect sediment and soil samples from beneath the harbour floor and undertake specialised testing to measure the strength and stability of the ground to depths of up to 15m.

At five of the investigation sites, sediment samples would also be collected and tested for the presence of environmental contaminants as part of the ecological assessment.

The investigations were expected to take up to two weeks to complete, depending on weather and tidal conditions. No disruption to residents or harbour users is anticipated, the council said.

“With the current outfall pipeline nearing the end of its operational life and experiencing multiple leaks, we’re working to address both the current infrastructure issues and future regulatory requirements,” Ertel said.

“Understanding the ecological conditions and the nature of the harbour floor is essential and the results from this survey will help us determine the best construction method to ensure a replacement pipeline can be safely and responsibly constructed, if that becomes the preferred solution.”

The community would have an opportunity to provide feedback on the proposed wastewater disposal solution once all technical and environmental assessments are completed, the council said.

For more information on the Katikati Wastewater Disposal Future Directions Project, visit: https://yourplace.westernbay.govt.nz/katikati-wastewater-disposal.