Calls for wastewater to be discharged on land instead of on waterways


Raw wastewater from the Ōmakau wastewater plant was flushed into the Manuherikia River in July 2022. file photo.
Photo: Delivered

With excessive flooding becoming more common, the mayor of Central Otago is pushing for a rethink of 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 posed in Central Otago after the Manuherekia River flooded Ōmakau’s sewage treatment plant in July, washing the city’s waste into the river for eight hours.

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

It was a bizarre event. Just five years ago, however, another bizarre event occurred.

Central Otago Mayor Tim Cadogan said they would become more frequent.

“These are monstrous streams that come out of nowhere and we would 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 move forward and prepare for it ,” he said.

Future-ready would mean moving the city’s sewage ponds, improving the quality of treatment, and then pumping the city’s wastewater uphill to eventually discharge it onto land.

The council knew the July event couldn’t become a regular, but fixing the situation could cost tens of millions of dollars, Cadogan said.

It was a dazzling amount, especially for a city of 800 and a district of 25,000.

But it was necessary to rethink the value of water.

“The majority of Central Otago households probably spend more on their Internet access than on the water they drink or cook with,” Cadogan said.

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“So is it that our water is getting too expensive or is it that we’ve never appreciated it?”

What happened in July was unacceptable and the council had to make quick decisions to minimize the risk of a recurrence.

But it was a result that came from past decisions about how wastewater was treated and disposed of, Cadogan said.

“In the past, decisions have been made based on what the cheapest option is and it would always remain the cheapest option if you just look at a way of looking at what something costs.

“That’s why you’ll find sewage treatment plants all over the country built right next to the river or they have a pipe that goes to the sea. They were decisions that seemed right at the time, but if you talked to manawhenua, they would I tell you that they never agreed that that was right So I think having a much louder voice in three waters than in the past will only be of value to New Zealand in the future as much as some people very nervous about it.”

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

“I had the privilege to [upgraded] The Cromwell wastewater plant – I think I was mayor for less than a year – and it discharges at a very high quality. But would I drink it? No. So why am I pouring it into the river,’ said Cadogan.

“I could say as mayor of Central Otago that we have this big river, so we’re fine. And as mayor of Central Otago, I could say that we have the Manuherekia and most of the time we’ll be fine. But at what point go we – none of this is good. None of this is good – pouring our human waste into the rivers, none of that is good.”

Despite the quality of Cromwell’s wastewater treatment, the municipality only received a reduction request last year due to increased nitrogen levels in the treated discharge.

Lake Dunstan Charitable Trust chairman Duncan Faulkner said Cromwell’s community group was also concerned about Cromwell’s wastewater eventually ending up in Lake Dunstan.

“I think it’s fundamentally flawed. I think the discharge into the rivers – Queenstown does the same thing and everything flows to us as well, just like Wānaka – there has to be a better way to manage this. The rivers are not sustainable in the long run.” term.”

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

But he wanted to have alternatives explored.

After dairy farmers along the Manuherekia River were targeted by David Parker during the 2017 election campaign, Andrew Paterson, owner of Matakanui Station, a sheep and beef farmer, examined the condition of Ōmakau’s treatment plant.

He discovered numerous problems with the factory and exposed the human impact of dumping waste into the river.

Plant upgrades improved the situation by 2018, but Paterson believed that the discharge of sewage into the river should stop.

Just as farmers played their game on what came from their properties, so should cities, he said.

“A lot of the systems run on dilution. With the wastewater in Ōmakau… it’s at very, very low E. coli levels and that’s with a fair amount of water in the river, you could literally drink. But the reality is that we’re still flushing our rivers.”

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Land removal was the way to go, Paterson said.

But there was a perception problem.

“The problem is changing our mindset so that people can land it. We have land that we can do that in New Zealand,” he said.

Disgust about the discharge on land made little sense, given the status quo.

“We’ve already taken it to the water and we don’t have people protesting at the Ōmakau wastewater treatment plant because the municipality is letting the water flow into the river. But we would have protests if we want to spread it to the country and it was against into the wind or it was next to someone’s house.”

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

Tim Cadogan said three water reforms made the most sense there

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

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

He said he didn’t want local decisions to be lost to a faceless administration hundreds of miles away targeting large settlements.

But tackling what to do with the country’s wastewater wasn’t just a problem for Central Otago, as most of New Zealand’s treated wastewater eventually ended up in a river, lake or beach.



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