Wet and forget: hole looms for town’s sewage problem

Is pumping treated sewage down a deep hole the answer to the wastewater headaches for small towns? David Williams reports.

Takapūneke, a small bay south of Akaroa, is culturally significant to Ngāi Tahu as the site of an 1830 massacre during a tribal conflict with Ngāti Toa.

The area’s modern use, as home to Akaroa’s sewage treatment works (and the now-closed rubbish dump), has long been considered inappropriate and culturally offensive.

The latest twist in a years-long debate about moving the sewage works is that Christchurch’s council, which governs the Banks Peninsula settlement, is seriously considering a little-used method of disposing of treated wastewater, called deep bore injection.

It involves sending the liquid down a hole, or a series of holes, drilled deep into the ground, below groundwater and below sea level.

The method is so infrequently used, that the only place in New Zealand thought to use the technique for public wastewater disposal is Russell, in the Bay of Islands. If it works in Akaroa, perhaps other small towns around New Zealand, which are also trying to find an affordable solution to disposing of its waste, will consider it.

That worries Massey University freshwater ecologist Mike Joy, who calls deep bore injection a “dangerous and scary cheap option”. “The only true solution is to cycle nutrients in wastewater proper land-based treatment or separate lines for grey and black water.”

About 70 people attended a meeting in Akaroa last week, at which the city council and its consultants outlined their plans. There were plenty of questions, says Suky Thompson, the deputy chair of environmental group Friends of Banks Peninsula, but not a lot of answers.

People are wary about pumping treated wastewater into the ground, she says, because the location is unknown, as is the underlying geology. “People are concerned in the rural areas that have been suggested because there are a lot of private water supplies.”

The city council is in the early stages of evaluating deep bore injection, which made an initial long list of options for Akaroa but was originally discarded. It’s hoped a test bore, or pair of bores, will be drilled next month. Depending on the results, the council plans to consult the public in the second half of the year.

“We’re just working really hard trying to find a solution and it’s difficult,” the council’s team leader of asset planning, water and wastewater Bridget O’Brien says. “There’s no silver bullet.”

“Imagine a Māori sewage treatment works being constructed on top of a European cemetery.”  – Harry Evison

As noted in 2012’s excellent Takapūneke Conservation Report, outrage over the location of Akaroa’s sewage treatment works were highlighted by historian Harry Evison in a Christchurch Press article he penned in 1995. “Imagine a Māori sewage treatment works being constructed on top of a European cemetery,” Evison wrote.

At least 100 people living at the kāinga (settlement) in 1830 were killed by Te Rauparaha and his warriors, helped by John Stewart, the English captain of the brig Elizabeth. After the massacre, Ngāi Tahu moved to the next bay south, Ōnuku. That’s where, in 1840, the Treaty of Waitangi was signed for the first time in the South Island.

The cultural significance of Takapūneke was recognised in 2002, as the first wāhi tapu area in Te Wai Pounamu (South Island). In 2008 – two years after the Banks Peninsula District Council was swallowed by its neighbouring city council – the area was declared a historic reserve, ending the threat of a proposed housing subdivision.

Yet the reserve still housed a wastewater treatment plant, which was now the responsibility of the city council. It had the unenviable task of finding a new site near Akaroa, among the generally steep terrain sloping down towards water.

Options were weighed and the council settled on a $30 million plan to build a new plant on Old Coach Rd, north of the town, with disposal via a harbour outfall pipe.

In 2015, the council got consents for its new plant – but not the outfall. Commissioners said an outfall was offensive to Ngāi Tahu and alternatives weren’t adequately investigated. (The council’s appealed the decision while it assesses other disposal options. Ngāi Tahu is involved in the appeal and wouldn’t comment on this story.)

The following year, proposals emerged for land-based disposal, including using treated wastewater for watering public areas and flushing public toilets. But residents of Robinsons Bay and the Takamātua Valley rose up in the face of plans to irrigate trees and pasture in their valleys. There were question marks over where effluent ponds might be built.

And then, another spanner in the works.

Faulty meter

In June last year, the flow meter at Takapūneke’s wastewater treatment plant was found to be faulty. Double the flows were, in fact, coming down the pipes. Therefore, work on reducing stormwater and groundwater infiltration into the system can only do so much. With those volumes – more than 300,000 cubic metres a year – more land and a bigger storage pond would be needed.

That’s when the originally-discarded idea of deep bore injection was dusted off.

City council’s O’Brien says it is relatively new technology for New Zealand. Beyond its use in Russell, similar technology is used to deal with stormwater in Auckland, Tauranga and Waikato. The Christchurch council’s consultants think it’s technically feasible.

O’Brien: “We’re not quite back to square one. We’re building on previous work; adding a new option.”

The beauty is, she says, if irrigation and deep bore injection can soak up all the wastewater, that eliminates the need for a large storage pond, needed for winter flows or when it’s too wet to apply to land. “You just put it down the bore instead.”

The main risk is to drinking water bores. O’Brien says that’s why any wastewater bore would be drilled deeper than water bores and there’ll be a buffer of at least 1.5km from any public water supply bore. Computer modelling suggests that for a site 400 metres from the coast, injected water will take months to a few years to reach the harbour, below sea-level.

Has the city council talked to the Far North District Council about Russell yet? No, says O’Brien, adding: “It’s definitely on our list of things to do.”

The biggest looming problem is the Takapūneke treatment plant’s consent, which expires in 2020. “The chances of us having actually built something and having it operational by 2020, when that consent expires, are becoming rapidly slimmer.”

The outrage over Akaroa’s despised sewage treatment plant seems set to continue for some years yet.

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