Reducing Overflows Into Harbour
Hatea Emergency Storage Tank

United Civil constructed a 1,000,000 litre underground storage tank in urban Whangārei, to reduce wastewater overflows into Whangārei Harbour during heavy rain.

This $4.8m project involved construction of the storage tank at depths of up to six metres 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 included:

• detailed design and construct components, including various piping, mechanical, electrical and control sub-systems needing to flocculate and UV disinfect any wastewater spilled from the storage tanks
• tanks and wet well construction next to a stream and in extremely poor soil conditions
• storage tank floor being cast insitu, along with pre-cast wall panels and a reinforced concrete topping slab to form the tank (undertaken by United Civil subsidiary Paneltech Construction)
• 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, the tank has eliminated many spills into the Whangārei  Harbour and helped achieve standards of water treatment that exceed design expectations.