The Kerikeri Wastewater Treatment Plant (WWTP) Project is the largest infrastructure project ever undertaken by the Far North District Council. Representing an investment of $27 million it is designed for expansion, to provide additional capacity to support growth in the northernmost district of New Zealand.

With a contract value of over $14 million, Ventia has played a significant role as the principal contractor in the design and construction of the new Plant, which will modernise wastewater treatment to meet Kerikeri's increasing needs and replace the existing, decades-old plant on Shepherd Road, which had been operating over capacity for some time and was no longer able to treat wastewater to the required standard.

Our team overcomes location challenges

Originally planned for a quarry site only 300m down the road, the location of the new Kerikeri Wastewater Treatment Plant was revised when a range of risks were identified in the Project's establishment phase.

The scale of earthworks as well as geotechnical issues such as the retention and stability of rock faces caused the team to reassess the viability of the location and recommend moving to a greenfield site close by that was more elevated and stable, reducing the risk profile and the overall cost of the Project.

While the site change would potentially result in a safer and more cost-effective outcome and secure the long-term viability of the new Plant, it did mean that adjustments to the site design were needed to ensure that the Plant design would be suitable for construction in the new location.

Wherever possible these design changes were identified early and the Ventia team worked closely with the Council's design consultants to minimise delays. The overall Project timeline was extended to accommodate the adjustments, which would ultimately achieve a better outcome for the client and the community.

End-to-end capital works management

Our work on the project comprised of extensive earthworks to clear and prepare the site, establishing 1.5km of access road and laying concrete slabs. The team also undertook the design and construction of multiple structures, interconnecting pipeworks and services, electrical design and fit out, and installation of a range of treatment systems such as UV, dewatering and dosing.

The new plant will treat up to three times the amount of wastewater the old plant was designed for and will discharge a higher quality of wastewater from its system using modern treatment methods.

After entering from the inlet and being screened for solid objects, wastewater travels into the aeration tanks of the sludge bioreactor where tiny sludge particles and compounds are removed through settlement and biological processes. Wastewater is then micro-filtered and ultra-sterilised under ultraviolet light to kill bacteria before leaving the treatment system.

As it leaves the plant, filtered and sterilised wastewater is clear in appearance and of a quality that will not impact on the surrounding habitat.

Pipeline construction for the Project was undertaken through the Waitangi Forest, Ventia worked closely with the land owners to ensure spill and silt control design measures, such as silt fences and cut off drains, were put in place to reduce any risk of environmental harm.

The new plant will serve all properties already connected to Kerikeri's wastewater system, plus 350 properties currently reliant on septic tanks who have been unable to connect to the former plant. It will also have capacity to serve up to 400 additional properties in the future. When completed and connected, the plant will ultimately extend service to more than 1400 Kerikeri properties.

Throughout this Project, Ventia has developed a strong working partnership with the Far North District Council, approaching all challenges with flexibility, adapting quickly to new circumstances and providing sound advice and expertise. The Kerikeri Wastewater Treatment Plan was successfully completed in October 2020 and with commissioning now completed it is fully operational.

Client and community outcomes

The new Plant will enable all Kerikeri properties to connect to a modern, high capacity wastewater treatment system that will help preserve the environment and serve the community into the future.