A Horizons Regional Council staffer wades into the water at South Beach to take a sample. Photo / Supplied
Whanganui's sewage outfall pipe at South Beach creates a great artificial surf break - but some surfers and the Whanganui District Council are at odds about the wastewater being discharged.
South Beach is a favourite place for surfers, with up to 50 a day using the area near the outfall and some going 1km from shore to get the best waves, surfer Allan Wrigglesworth said.
Mike Lamb, who also surfs there, said he sometimes sees brown particles in the water.
Wrigglesworth was a member of three previous wastewater working parties. He said wastewater is less dense than seawater, so it floats on top and can get pushed onshore by big incoming tides and light to moderate onshore winds.
The predominant current at the beach moves water south, taking the wastewater toward Kāpiti - but when there are southerly winds it can be pushed north as far as the Castlecliff Surf Club.
"I was out there ... surfing among this stuff and I'm not very happy at all," Wrigglesworth said.
"I want to know why the scheme isn't being operated as promised. The [ultraviolet] lights are meant to kill any remaining bacteria. If the water is too murky with suspended solids they will not be working."
But the surfers should not be too close to the outfall, a council spokeswoman said.
"Surfers and other recreational users are advised to stay outside the exclusion zone around the outfall. Warning signs are posted at the entrance to South Beach off Landguard Rd and also at the South Beach carpark advising this, as required under our discharge consent."
The UV process at the wastewater treatment plant was working, she said.
"We would be happy to have Mike Lamb, Allan Wrigglesworth and other beach users visit the plant, so they can be assured it is functioning as it should."
Lamb remembers a day in February 2014 when the waves were good and he went to South Beach to surf and found the road closed.
"I get down there and there was diggers, bulldozers, trucks for Africa."
They were scraping a substance off the beach and taking it away, just days before a big surfcasting competition. The substance was piled up between South Mole and the Kaitoke Stream, for about 500m.
"We were out surfing looking at toilet paper and faecal matter that looked like it had been through a sieve, but it had a chemical smell to it as well," he said.
The Chronicle was told at the time the substance taken away in trucks was not sewage. But current Whanganui District Council senior wastewater engineer Tony Hooper has now confirmed that it was.
Whanganui's wastewater treatment plant had failed, and screened - but not otherwise treated - sewage was being pumped out to sea.
"In 2014 the presence of wastewater material would have been completely expected as at this time all wastewater was screened at the Beach Rd pumping station – there was no wastewater treatment plant and our short-term consent with Horizons allowed for wastewater to be pumped out to sea," Hooper said.
Lamb said the situation had improved a lot since then. He still sometimes saw traces of wastewater out near the outfall, but said it probably doesn't reach the beach.
Hooper said these days, discharges of screened but not otherwise treated waste only happened at times when very heavy rain overwhelmed the wastewater treatment plant.
"During these times we discharge partially treated wastewater, screened to remove solids. This is allowed by Horizons Regional Council, in line with our consent to divert screened wastewater directly to sea once flows to the plant reach 1120 litres per second."
Dry weather flows vary from 200-500 litres per second. Wet weather can increase the flows fourfold.
The level of enterococci in bathing water at South Beach exceeded limits set by Horizons three times last summer.
The limit breaches happened in January, February and March, Horizons regulatory manager Greg Bevin said.
A level eight times the limit reported by RNZ was a mistake, related to a misreading of data from Whanganui District Council. Last summer's breaches were not eight times the limit of 104cfu/100ml, Bevin said.
The samples were taken by Whanganui District Council and ranged from 110cfu to 330cfu/100ml. Horizons was considering whether this was a moderate or a significant noncompliance.
Most of the time enterococci levels at the beach are well below the 35cfu median limit set by Horizons - and hugely below the 890,000 to 4,800,000 cfu/100ml of raw sewage as it arrives at the wastewater treatment plant. In fact the annual median result was 4cfu/100ml.
The LAWA website says the beach has been 100 per cent suitable for swimming this summer. For the previous five years it was 98 per cent suitable, with the highest enterococci reading of 360cfu/100ml.
The council takes weekly water samples at six sites, as required.
Sampling, done by Horizons during the swim season, has shown no risk to swimmers.
However, the high levels the district council found last summer should have been notified to Horizons within 10 days, and were not. That condition was important because the regional council was not there most of the time, Bevin said.
"We have picked up that they haven't done that, and gone back to them on that."
Enterococci are organisms found in human and animal faeces, and can indicate the presence of other organisms that can cause disease. They can survive in salt water.
Whanganui District Council chief executive Kym Fell has said the enterococci level was raised last summer by onshore winds pushing wastewater into the coast.
Bevin said there could have been other factors too, such as additions from water drifting down the coast from the Whanganui River.
Wastewater from the outfall is sampled as it leaves the Whanganui wastewater treatment plant after disinfection by ultraviolet lights.
From there it goes into the pipe that takes it to the outfall 1.8km off South Beach. It gets diluted as it disperses into the sea from the end of the pipe.
The ultraviolet lights will only work to kill bacteria if the water is reasonably clear, Bevin said.
"The UV light blasts the bugs. If the water is turbid the bugs hide behind fine sediment particles."
At February's infrastructure committee meeting Whanganui district councillors were told UV disinfection had been causing issues. However, the equipment supplier had returned to the site to train staff and a local contractor who would be able to fix future problems.
It was unclear whether the high levels of chromium at the treatment plant, from Tasman Tanning's wastewater, were causing the high enterococci levels but Fell has previously said high levels of chromium in the wastewater stream could create bacteria die-off within the treatment process.
Riders and spectators in Whanganui are anticipating the start of the last race.