The stench from the massive raw sewage discharge at Moa Point in Wellington may worsen as Wellington Water grapples with a new sewage overflow issue in Porirua.
Since early Wednesday, tens of millions of litres of raw sewage have contaminated the ocean around Wellington’s south coast. This occurred after the Moa Point Treatment Plant was flooded with raw sewage, prompting its shutdown and evacuation – a situation described by the capital’s mayor as a ‘catastrophic failure’.
Wellington Water is now racing against time to clear the sewage inundation from the Moa Point Treatment Plant before it turns septic and becomes anaerobic. Anaerobic smells occur when bacteria breaking down decaying material lack access to oxygen, typically in a confined mass of biodegrading material.
If the sewage becomes septic and anaerobic, it could emit a noticeable odor and pose significant health and safety risks for on-site workers, Wellington Water warned. Crews are currently focused on emptying the clarifier tanks to separate biological sludge from treated wastewater. However, this process may result in a stronger smell and a plume in the ocean near the outfall pipe.
Contractors will soon investigate the plant’s power system and equipment to assess the extent of damage once the tanks are emptied. Residents are advised not to collect seafood or walk dogs along the beach in the affected area.
Overflow Incident in Porirua
Another wastewater overflow was reported at a Wellington Water site in Porirua, near the intersection of Mana Esplanade and Pascoe Avenue. Initial investigations suggest the overflow may be linked to a pump running sequence at Pump Station eight.
Although the overflow has ceased, access to the affected manhole would require excavation of the state highway. As a result, no immediate action is planned, but the site is being monitored, with environmental controls in place along Mana Esplanade.
Efforts at Moa Point Treatment Plant
Following the flood at the Moa Point Treatment Plant, sewage spilled from a short pipeline directly into the southern coastline. Wellington Water has begun pumping the wastewater through a longer outfall pipe, screening out items like wet wipes before discharge.
Some of the spilled sewage has been taken to landfill, while the remainder is being pumped through the 1.8km outfall pipe to minimize beach contamination. The short outfall pipe did not discharge wastewater overnight from Friday to Saturday.
Wellington Water’s board chair, Nick Leggett, emphasized the focus on cleaning the plant to ensure a safe working environment and prevent foul odors. Site and coastal cleaning, as well as sampling, are ongoing.
Divers have inspected the outfall pipe for blockages, but none have been found yet. Wellington Mayor Andrew Little plans to discuss the plant failure with Prime Minister Christopher Luxon, highlighting the need for investigation and prevention of future incidents.
“We cannot allow such critical infrastructure to fail and cause environmental harm,” Little stated. “Understanding the facts and implementing preventive measures is crucial to avoid a recurrence.”
