Reducing Overflows Into Harbour
Hatea Emergency Storage Tank

In order to reduce wastewater overflows into Whangarei Harbour during heavy rain, construction of a 1,000,000 litre underground storage tank was proposed in urban Whangarei. The tank would help to minimise infiltration into existing pipe networks during heavy rain, and therefore overflows into Whangarei Harbour.

This $4.8 million project involved construction of the storage tank at depths of up to 6m below existing ground level, with the added complication of extremely poor soil conditions. The new tank also featured UV disinfection, and a replacement sewer pump station, which was successfully integrated into the existing sewer reticulation scheme.

Key Challenges:

  • Detailed design and construct components, including various piping, mechanical, electrical and control sub-systems needed to flocculate and UV disinfect any wastewater spilled from the storage tanks
  • Tanks and wet well being constructed next to a stream, and in extremely poor soil conditions
  • Storage tank floor being cast in-situ, along with pre-cast wall panels and a reinforced concrete topping slab to form the tank, undertaken by United Civil subsidiary Paneltech Construction
  • Required management of multiple subcontractors, including client-nominated specialists and structural designers

This successfully executed design solution has provided exceptional ongoing performance. Completed without incident and within the agreed timeframes, post-contract performance has been high, eliminating many spills into the Whangarei Harbour and achieving standards of water treatment that exceed design expectations.