Half-tonne fatberg in Gisborne blocks the wastewater network

The fatberg found in Wainui Rd last year. Photo / LDR

Two years after $100,000 was spent jet cleaning a "fatberg" from Gisborne's sewer network, a half-tonne mass of largely fat, wet wipes and rags built up in the same place.

The second fatberg was found blocking the wastewater network on Wainui Road near the Mobil service station after minimal rain caused an overflow of the wastewater system on June 26 last year.

Gisborne District Council was forced to open the emergency sewer valve, releasing wastewater and sewage into the river.

It cost the council another $15,000 to clear the blockage at Wainui Road.

Workers used picks, shovels and high-pressure hoses to clear the 15-metre-long mass made up of lots of solid fat, rags, wet wipes and condoms.

This was one of three overflows during a six-week period between June and mid-July 2020, according to an annual report of wastewater activities that came before the council's wastewater committee last week.

Some of the overflows were "unexpected" considering the intensity of the rain, the report said.

Council infrastructure manager Neville West said they had taken a "more proactive" approach to clean known problem areas, and in positive news, heavy rain late last year did not result in an overflow.

West said blockages were a "major challenge" but they had increased budgets for jet cleaning to remove fatbergs.

"What we're actually getting through is a lot of wet wipes and this is a national issue that's come about in the last five years," he said.

Workers spent most of a day using picks, shovels and hoses to break down the fatberg after it caused an overflow to the wastewater system. Photo / LDR

They had modified their regime for some areas, but knowing where the blockages were was a challenge.

"The difficulty we've got is in certain weather events we don't expect overflows, — we haven't had the quantum of rain, yet we've had the overflows.

"They're kind of unexplained, so we have to go looking for (the block), and remember we've got 222km of pipe so it's kind of almost a needle in a haystack scenario."

Through the Covid-19 period, they had "significant problems" with pump stations blocking because more people were at home and their behaviour had changed, he said.

"But what we can say, is in a recent rainfall event we had 75ml of rain. Normally that would have probably driven us to an overflow. We can actually say that we weren't even close to coming near an overflow.

"So the work that the DrainWise team are doing now with regards to the removal of downpipes into gully traps and sealing damaged gully traps, and the improved jet cleaning programme, appears to be starting to pay dividends."

Other issues mentioned in the annual wastewater report included a burst private water pipeline flowing into a private wastewater manhole, new cross-connections between stormwater and wastewater, a collapse in the Anzac Rd sewer main and the "catastrophic failure" of the Oak St sewer pump due to something hard washing down.

The council has previously made calls to the public that "sinks are not rubbish bins" and to "please only flush the 3 Ps — pee, poo and toilet paper".

They have also reminded the public that wet wipes should go in the rubbish bin, not the toilet.