Sometimes, fountains of brown water, toilet paper and sanitary products pour out of manhole covers on to South Dunedin’s Surrey St, most often outside a car repair garage at the intersection with Hillside Rd.
It has happened at least twice in the past eight months and the problem has been flagged for decades by Surrey St residents and in engineering reports.
There are elderly people living here, in private houses and a care home. They love it, because it is flat and easier on dodgy hips and knees.
The flat land means sewage can linger. The brown horror has even bubbled up into toilet bowls and shower trays.
"Cats can pad it in to our houses and trample it into the carpet," added Lynne Newell, convener of the Surrey Street Flood Action Group, which has taken its concerns to the health minister and the ombudsman.
Why does it happen?
Dunedin’s wastewater — including from our toilets — should all go into sealed wastewater pipes that go to treatment plants that make the wastewater safe before it is disposed to land or water.
That’s the idea, anyway.
To protect people and biodiversity, untreated wastewater should never enter a street or anywhere else, including rivers or the ocean.
The council has known about the problem on Surrey St for decades. An essential pipe network built by previous generations has decayed beneath the residents’ feet and its contents now occasionally slosh around ankles.
Old, broken wastewater pipes have holes and unsealed joints causing rainwater to seep in. The pipes get too full, leading to overflow through manhole covers. Pipe engineers call it infiltration.
The city’s growth may be a factor. There is more wastewater and sometimes more stormwater due to pipes from roofs being wrongly plumbed into the wastewater system.
Surrey St also lies in the sink of Dunedin. A significant proportion of the city’s wastewater, including infiltration, passes through here on its intended journey to the Tahuna wastewater treatment plant and, post treatment, disposal into the Pacific Ocean.
Multiple wastewater pipes — including two pipes from Kaikorai Valley via the Caversham tunnel — join up outside the Surrey St garage.
An old system was constructed to channel any excess wastewater from here into a stormwater pipe travelling a northerly route along Hillside Rd to the Portobello pump station.
It is substandard. Objects such as sanitary products can be caught in a screen there, but wastewater can only be dumped, untreated, into the harbour. Unsurprisingly, and tellingly, the route is described in reports as a "contamination vector".
Worse, it is ineffective. The wastewater sometimes pours out the manhole cover at the top of Surrey St and streams down the street and also round the corner on to Hillside Rd — past ground-level shops including food businesses and towards the care home. It pools in gutters, drives and gardens.
Wastewater further down Surrey St can also come from the single wastewater pipe that runs along it.
Council Three Waters group manager John McAndrew said the pipe could become full during "periods of heavy rain and high wastewater flows".
The wastewater could then bubble up through other manholes and slosh back into properties’ drains and houses.
Surrey St runs parallel to the bottom of the St Clair hillside, which also suffers from drainage problems, causing more run-off on to the street.
Action, not reflux valves
When asked about sewage on Surrey St, the council often mentions the vertical pipes that stick up in some houses’ flower beds. The pipes — fitted by the council — connect to horizontal wastewater pipes leading from people’s homes to the street’s main wastewater pipe, and contain a non-return valve, commonly called a reflux valve.
When the main wastewater pipe is full, a flap closes, stopping sewage sloshing back up the pipe and into houses.
However, if a house has a reflux valve fitted, flushing the toilet and showering lots is a bad idea when there is sewage in the street. The valve is shut and wastewater can’t flow out.
Not every house has a reflux valve, and real estate agents don’t mention them when trying to sell houses here, but Ms Newell’s action group will not be silenced.
They want action and want it now.
The council responds
Last week, the Otago Daily Times asked the city council what measures had been undertaken to stop the slurry on Surrey, their cost and timing and how the problem would be fixed now.
The paper asked the council not to respond by talking about reflux valves.
The council’s Mr McAndrew stressed that wastewater management was an "important public health service and we take our responsibilities extremely seriously".
The council had previously analysed options for "longer-term and expensive changes" to the network, including diverting flows from Kaikorai Valley to the Green Island wastewater treatment plant.
He said funding for this project was in the council’s 10-year plan in 2018 but the project was paused "after reviewing the capacity of the Green Island plant".
The council had also reviewed an option to discharge treated wastewater to the Kaikorai Stream, but this was also paused, around 2019, due to a "number of factors".
Mr McAndrew said 23km of new wastewater pipes had been installed in the city, including 9km of pipes in Kaikorai Valley since 2012 and pipes in North East Valley and Andersons Bay. The work aimed to reduce the infiltration problem, including the Surrey St "bottleneck".
A further 1.5km of pipes in Kaikorai Valley are being replaced.
The length of old wastewater pipes still in service — in Kaikorai Valley, South Dunedin, or elsewhere — was not provided.
Ms Newell worries that if Surrey St gets a new pipe, the problem might shift to another street closer to Tahuna.
Mr McAndrew talked about the reflux valves, but acknowledged they are "an interim measure — not the final solution".
The council was working on "best options for a permanent fix to the Surrey St situation".
‘Complex and expensive’
Mr McAndrew said the issues and options were "complex and expensive, so we need to plan carefully but progress is being made and we expect to be able to release further information later this year."
An "Integrated System planning project" had finished and helped the council understand its entire network and how changes in one area impact another.
The work had informed a short-term package of work called "Wastewater Network Optimisation" that would be completed this year and inform the preferred option for Surrey St.
Mr McAndrew said many possibilities were on the table.
"We don’t have a short list yet, but the options we’re considering include a mix of storage facilities, overflows, increases in pipe capacity and diversion of some flows."
The timeframe for delivery would depend on the option chosen.
Last year, when the ODT asked similar questions, the paper was told there would be "a plan for work" by mid this year.
There isn’t, locals have had enough, and Mr McAndrew finds himself having to explain the ongoing Surrey St problem by finger-pointing previous regimes.
"DCC is catching up on historical underinvestment in infrastructure renewals, which has left us with old pipes in need of replacement and a network in need of change," he said.
What is happening now
The council says it is, concurrently, stumping up $60 million in its nine-year plan for "wet weather flow management improvements", including in South Dunedin, plus another $44.2m for South Dunedin "flood alleviation work", of which $29.2m is for three "short-term" projects approved in January this year.
A $15.2m project will disconnect the Hillside Rd stormwater mains and pump water to the Orari St stormwater outfall and into the harbour.
A $12m project will install a bigger stormwater pipe on Forbury Rd, which runs behind Surrey St, hopefully helping reduce run off from the St Clair hills into Surrey St.
A $1.9m project replaces a stormwater pipe closer to the Portobello Rd pump station at an estimated cost of $1.9m.
Neil Johnstone, a retired water engineer and member of Ms Newell’s action group, says the three projects would have "zero impact" on the main cause of Surrey St’s woes — the volume of polluted water coming through the Caversham tunnel from the Kaikorai Valley catchment.
He points out that the planned projects are happening a decade after South Dunedin’s catastrophic 2015 flood.
They also would not be delivered until 2028 at the earliest, as they are still at the design stage.
Fellow campaigner, Ms Newell, was focused on a response from the ombudsman.
She said the council had repeatedly fobbed off complaints and the issue "should be taken out of council’s hands and an independent investigation begun on the situation".
She brought the issue back to the elderly locals.
"Who’s going to die before this gets fixed?"
