Wellington's $1b wastewater problem and it's not Moa Point: Warnings over Seaview plant

A top water official in the capital is warning of the consequences if another major wastewater treatment plant in the city critically fails.

The Seaview plant in Lower Hutt has been plagued by stench issues in recent years, and its 18-kilometre-long sewage pipe into Cook Strait is leaking.

The pipe replacement could cost up to $1 billion.

Wellington Water admits the situation is unacceptable as it's forced to spill treated sewage into a stream that's sacred to local iwi - though it's adamant the plant can't fail in the same way as Moa Point did.

Wellington Issues reporter Ellen O'Dwyer has more.

When Kura Moeahu was a boy he recalls the Waiwhetū stream as a flowing river - rich and vibrant with life.

"I remember walking up the river as kids, and we would go get those glow-worm worms to enable us to go bobbing. So that at night, we'd be in the river here, and pulling kai out."

The chair of Te Rūnanganui o Te Āti Awa and Whaiwhetū Marae said the waterway, which carves its way through eastern parts of Lower Hutt past the Seaview wastewater treatment plant, is sacred.

Once heavily polluted by industrial waste, Moeahu said people have been trying to restore the stream for decades.

But for years, Wellington Water has been emptying treated sewage into the stream because of the Seaview treatment plant's degrading sewage outfall pipe.

The pipe could only take half the sewage it was built for, so the wastewater is pumped into the stream when it rains, or when the pipe is being fixed, Wellington Water's chief operating officer Charles Barker said.

Te Āti Awa has raised concerns about the environmental effect for years.

Moeahu - a grave digger at the Owhiti Urupā - said after a hard rain the discharges are gruelling for those preparing to bury the dead.

"As a digger, particularly if you're digging closer to the stream, when you start going down four-foot, and it's high tide, the impact of the stench comes through the sand, because it's sand that we dig - and it has an impact."

'A failure' could have 'enormous' implications

At a meeting between water officials and mayors in the capital in May, Tiaki Wai board chair Will Peet revealed he'd been worried about the Seaview plant for some time.

"When I got the phone call about Moa Point, I thought it was Seaview... and so if you want to bring that into sharp relief - you've got a long, very long outfall, you've got a plant at the bottom of the harbour, in the eddy of a river."

Peet said Wellingtonians must make big decisions about Seaview's long pipe, which runs past Eastbourne, past Pencarrow Head and into Cook Strait, and is leaking.

Built in the 1960s, the pipe is 18km long, and according to Barker, the 4000 rubber joints in it are deteriorating.

A section of the pipe leaked in March - spilling treated sewage into the stormwater and coastline around Marine Drive.

"It's 18 kilometres long, I think, in four and a half metre sections - it leaks, and that's a big decision for the community," Peet said.

"A failure at Seaview will have enormous implications for our harbour and Whanganui-a-tara".

Seaview can't fail in the same way Moa Point did - Wellington Water

In March Lower and Upper Hutt council executives called a meeting with Wellington Water to seek assurances the plant wouldn't fail like Moa Point did, when it flooded in February.

Barker told RNZ a Moa Point failure at Seaview isn't possible, because of the plant's design layout.

"If a part of [the outfall pipe] collapsed, we would sense that straight away, because the pressure would change in the pipe, and that would lead directly to a discharge into the Waiwhetū stream - and would prevent a discharge coming back into the plant."

However he said the pipe's condition is not good enough.

"Frankly it's every decent weather event, and every decent rainfall, some level of discharge will go into the Waiwhetū stream, which is just unacceptable."

He said work had been underway with Hutt councils and mana whenua to consider a number of solutions for the degrading pipe - this would pass to new entity Tiaki Wai on 1 July.

Fixing the pipe would take years, Barker said, and involve digging up sections of coastal road.

When five of the rubber joints failed in 2009, it took seven months to fix, Barker said.

Barker said it now looked cheaper to build a whole new pipe - estimated to cost between $700 million and $1 billion - but no decisions had been made, including the location of a new pipe.

"We have to make sure we do a really sound investment. We can't spend $700 million of the community's money, and not have a much better solution."

Moeahu said the region needed to grapple with a solution now.

"It falls on deaf ears when you hear this is unacceptable, this is unacceptable, this is unacceptable.

"What we're interested in what is the solution to it? Then we could probably say - yes we accept that now, but it's unacceptable to say it without a solution."

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