Wellington Water undertaking UV system replacement at Moa Point

Wellington Water, on behalf of Wellington City Council, is continuing its programme of upgrades at the Moa Point Wastewater Treatment Plant with the replacement of the plant’s ultraviolet (UV) disinfection system, starting from 1 October to May 2026.

These works follow the recent refurbishment of the plant’s three clarifiers, along with the replacement of pipes and pumps at its pump station.

“The UV system, which forms the final stage of the treatment process, is aging and urgently needs upgrading,” says Jeremy McKibbin, General Manager Treatment and Control Systems at Wellington Water. “It plays a critical role in disinfecting wastewater before it is safely released into the ocean between Te Raekaihau Point Reef and Hue te Taka.”

During the upgrade, the plant’s treatment capacity will be reduced while each of the two UV disinfection channels are taken offline, one at a time. On rainy days, when wastewater volumes are higher than usual, all wastewater will go through initial screening and grit removal. However, some wastewater may bypass the full biological treatment and UV disinfection process.

This partially treated wastewater will then be combined with fully treated wastewater and be discharged via the long outfall pipe 1.8km offshore. Discharges in this location, will be heavily diluted due to significant tidal flows.

An environmental impact assessment indicates that most of the discharges are expected to last a short period, with a low overall environmental impact. Water quality sampling will be undertaken following rain and plant discharges.

“Moa Point, like other treatment plants in the region, is aging. These upgrades are essential to ensure safe, effective operation and to reduce environmental impacts. While operating at reduced capacity isn’t ideal, this work is critical to prevent future UV system outages. We’ve timed it for the drier months to reduce the frequency of partially treated wastewater being discharged,” says Jeremy.

The upgrade is expected to take around eight months to complete. During this time, recreational water users are advised to follow public health guidance and avoid swimming for two days after rain at South Coast beaches, particularly Lyall Bay, Princess Bay, and Tarakena Bay.

Wellington Water wants to reassure the public that the plant can still fully treat the normal amount of wastewater during dry weather.

 “On days it doesn’t rain, the plant will operate as normal. There’s no impact on how it treats wastewater. People can be confident the plant is still doing its job effectively,” says Jeremy.

“Our key message to the public is, if you’re considering going for a swim or doing other recreational activities at the South Coast beaches on rainy days, please check with LAWA first.”

The public can access the latest recreational water quality information on the Land, Air and Water Aotearoa (LAWA) website.

Wellington Water meanwhile is engaging with mana whenua and the local community to minimise environmental and public health risks. Temporary signage will be installed at key shoreline locations when there is an increased risk to water users, and updates will be shared via social media and the Wellington Water website.

“This upgrade will improve the long-term performance of the plant, reduce environmental impacts, and increase resilience,” says Jeremy. “We’re committed to keeping the community informed and safe throughout the project.”