Calls for wastewater to be disposed on land rather than waterways

With freak flooding events increasing in frequency, Central Otago's mayor is pushing for a rethink on wastewater disposal and questioning whether it should be discharged into waterways.

Is it time to stop treating our lakes and rivers like toilets?

That's the question being posed in Central Otago after the Manuherekia River flooded Ōmakau's sewage treatment plant in July and washed the town's waste into the river for eight hours.

The Manuherekia River has a median flow of eight cumecs but during July's downpours it raged at 430 cumecs.

It was a freak event. However, another freak event occurred only five years ago.

Central Otago mayor Tim Cadogan said they would become more common.

"These are monstrous flows that are coming out of nowhere and we'd be foolish to go it's an aberration, or it's El Niño, or it's this or that. It's the future and we need to get a move on and get ready for it," he said.

Getting future-ready would mean moving the town's sewage ponds, improving treatment quality and then pumping the town's wastewater uphill for it to be ultimately disposed on land.

The council knew it could not let July's event become a regularity, but remedying the situation could cost tens of millions of dollars, Cadogan said.

It was an eye-watering sum, especially for a town of 800 and a district of 25,000 people.

But rethinking the value of water was needed.

"The majority of households in Central Otago probably spend more on their internet access than they do on their water that they drink or cook with," Cadogan said.

"So is it that our water is becoming too expensive or is it that we've never valued it?"

What occurred in July was unacceptable and the council needed to make decisions quickly to minimise the risk of it repeating.

But it was an outcome borne from decisions of the past about how sewage was treated and disposed, Cadogan said.

"In the past decisions have been made based on what's the cheapest option and it would always remain the cheapest option if you're only looking at a dollars and cents way of looking at what something costs.

"That's why you'll find wastewater treatment plants right across the country built right next to the river or they've got a pipe going out to sea. They were decisions that at the time seemed right, but if you talked to manawhenua they would say to you they never agreed that was right. So I think iwi having a much louder voice in three waters than they have in the past is only going to be of value to New Zealand into the future as much as some people are very nervous about it."

The bigger question was whether wastewater should ever be discharged into waterways.

"I had the privilege of opening the [upgraded] Cromwell wastewater plant - I think I had been mayor for less than a year - and it discharges to a really high quality. But would I drink it? No. So why am I pouring it into the river," Cadogan said.

"I could say as mayor of Central Otago we've got this big river, so we're all right. And I could say as mayor of Central Otago we've got the Manuherekia and most of the time it's going to be fine. But at what point do we go - none of it's fine. None of this is fine - pouring our human waste into the rivers, none of it is fine."

Despite the quality of Cromwell's wastewater treatment, the council received an abatement notice only last year due to increased nitrogen levels in the treated discharge.

Lake Dunstan Charitable Trust chairperson Duncan Faulkner said the Cromwell community group also had concerns about Cromwell's wastewater ultimately ending up in Lake Dunstan.

"I think it's fundamentally flawed. I think discharging into the rivers - Queenstown is doing the same thing and that all flows down to us as well, as is Wānaka - there has to be a better way of managing this. Just tipping it into the rivers isn't sustainable on a long-term basis."

The trust had actually started monitoring Lake Dunstan's water quality near the discharge site, Faulkner said.

But he wanted alternatives investigated.

After dairy farmers along the Manuherekia River became the target of David Parker during the 2017 election campaign, Matakanui Station owner Andrew Paterson - a sheep and beef farmer - investigated the state of Ōmakau's treatment plant.

He uncovered numerous problems with the plant and exposed the human impact of waste being discharged into the river.

Upgrades to the plant improved the situation by 2018, however, Paterson believed discharging wastewater into the river had to stop.

Just as farmers were upping their game on what came off their properties, so too should towns, he said.

"A lot of the systems work on dilution. With the wastewater at Ōmakau ... it's at very, very low E coli levels and that's with a reasonable amount of water in the river, you literally could drink. But the reality is we're still flushing it down our rivers."

Land disposal was the way to go, Paterson said.

But there was a perception problem.

"The problem is changing our mindset so people are allowed to put it on to land. We've got land that we can do that in New Zealand," he said.

Distaste over discharging to land made little sense, considering the status quo.

"We've already got it going to the water now and we don't have people protesting at the Ōmakau wastewater plant because the council's putting the water into the river. But we would have protests if we want to spread it to land and it was upwind or it was next to someone's house."

But if discharging to land was the future, how would the district pay for it?

Tim Cadogan said that was where three waters reforms made the most sense

Spreading the cost of such upgrades over 800,000 people rather than 25,000 (or 800) made them more feasible and achievable in a reasonable timeframe.

Andrew Paterson on the other hand was vehemently opposed to the government's reforms.

He said he did not want local decisions being lost to a faceless board based hundreds of kilometres away with a focus on large settlements.

But tackling what to do with the country's wastewater was not just a problem for Central Otago, with the majority of New Zealand's treated wastewater ultimately coming to a river, lake or beach.