Wellington sewage spill: Map shows where the waste in Wellington’s ocean is drifting

As Wellingtonians question where they can safely swim this summer, a new map has been designed to help them track where the sewage in their ocean is flowing.

The Moa Point wastewater treatment plant completely failed on Thursday, pumping raw untreated sewage directly into the ocean.

Officials have said the south coast of Wellington is unsafe to swim in – potentially for months.

The waste is now partially treated and workers have been able to switch to a longer outfall pipe, pumping waste about 1.8km out to sea.

Calypso Science, a New Zealand company offering physical oceanography around the world, created the map alongside Oceanum.

Physical oceanographer Remy Zyngfogel told the Herald the company made the map “because we wanted to do it, nobody asked us to do it”.

Calypso Science's pollution map tracks the sewage dump on Wellington's south coast.

Zyngfogel made it clear that their map is not part of the council or Wellington Water’s work.

“It doesn’t replace sampling Wellington Council is doing, that should be the primary source.”

He said the map was there to help people understand the big picture of what the current is doing.

“It’s mainly an indicator of how the plume behaves depending on the wind and tide.”

Using two models – Schism and OpenDrift – the company calculates the currents and particles to determine where the sewage is.

The Schism model stands for Semi-implicit Cross-scale Hydroscience Integrated System Model and is used to simulate physical and ecological processes across small to large bodies of water.

OpenDrift is a software which models the trajectories of substances or objects drifting in the ocean, or even in the atmosphere.

Calypso Science specialises in ocean currents, working in Australia, Europe, South America and New Zealand.

Sewage can be seen on Wellington's south coast after a leak from the Moa Point wastewater plant. Photo / Kate Taptiklis

Speaking on Ryan Bridge TODAY, Wellington Water chief executive Pat Dougherty said 70 million cubic metres of sewage a day was discharging into the water – averaging between 1300 and 1400 litres a second.

“It still looks like about 80% of our plant was submerged or partially submerged, and it’s going to be months before we get that fixed.”

It will be unsafe to swim anywhere along Wellington’s southern coastline until the plant can be fixed, Dougherty said.

“It’s completely unacceptable, we acknowledge that, but as I said the last time we talked, public health is the priority.”

Wellington Mayor Andrew Little wants to see an independent inquiry, sponsored by the Government, into the mechanical failure.

A number of organisations are involved. Wellington City Council owns the Moa Point Wastewater Treatment Plant site, Wellington Water is contracted to run the region’s water network, waste management company Veolia is contracted to run the plant and Greater Wellington Regional Council has regulatory oversight.

“It just needs somebody who’s independent of all those bodies to step in [and] see who knew what when,” Little said.

He wanted the inquiry to “see whether any red flags were raised” as well as work out what had happened, whether there were design faults and investigate the quality of Veolia’s work.

Sammy Carter is a journalist for the New Zealand Herald covering news in the Wellington region. She has previously worked at the Rotorua Daily Post.