Green Scorpions sting City over vlei pollution

The Archimedes screws at Strandfontein sewage works, which lift sewage into the sewage plant, are broken.

The Green Scorpions are taking the City to task over a sewage spill in Zeekoevlei – just one of three ecologically sensitive wetlands, including Zandvlei, closed because of pollution.

The environmental inspectors from the Department of Environmental Affairs and Development Planning have ordered the City to explain the cause of the Zeekoevlei spill and what it plans to do to clean it up.

The scope of the order does not extend to Zandvlei and surrounds, according to Marian Nieuwoudt, mayoral committee member for spatial planning and environment.

“The causes of water pollution in Zandvlei are under investigation but are not linked to the Zeekoevlei incident,” she said.

The City has confirmed significant damage to the Archimedes screws at the Strandfontein sewage works. The screws are pumps that lift raw sewage from the inlet sumps, into the sewage plant.

The False Bay Echo was alerted to this by Zandvlei Trust chairman David Muller, who said an estimated 105 million litres of raw sewage had entered Zeekoevlei over a 24-hour period on Monday July 12. That was about 10% of the total volume of Zeekoevlei when full, he said.

“I understand this will continue into Rondevlei. Zandvlei has been closed for any form of recreational use for two months now. Such effluent will end up in the sea endangering our lives too. I won’t mention Rietvlei in Milnerton,“ he said, referring to the other City wetland that has been closed because of pollution. Rietvlei’s E coli levels were found to be 30 times higher than what is considered safe. “If ever there was a time for the City to act – it is now,” he said.

However, Xanthea Limberg, mayoral committee member for water and waste, said the failure of the Archimedes screws would not have led to spillage in Zeekoevlei because the sewage would spill over the sump and into filtration holding ponds at the treatment plant.

Instead, she said, the “compounding effect” of damaged manholes and high volumes of stormwater entering the system had caused the spill into Zeekoevlei.

The Strandfontein sewer works had been unable to cope with the ingress of stormwater, resulting in a backup in sewer lines across the False Bay Nature Reserve and Cape Flats, causing multiple sewer overflows across several suburbs, including Lotus River, Grassy Park, Phumlani, Pelican Park and New Horizon, with subsequent drainage into Zeekoevlei.

The City had been using temporary pumps to get sewage into the treatment plant, since the incident reported on Monday July 12.

Two new gearboxes for the screws would be delivered by the end of the month and should take about two weeks to install. Ms Limberg said those gearboxes had been ordered some time back.

“It is hoped that four screw pumps will be operational (one to two in operation and two on standby), two with new gearboxes and two with refurbished gearboxes,” she said.

Only one Archimedes screw had worked all winter last year, and yet there had been no spillages, she added.

The Archimedes screws have experienced previous gearbox failure, in both 2014 and 2018, with damage caused by bulky objects dumped into the sewer system, such as gas canisters, she said.

They were replaced in 2018.

The cost of the four new gearboxes for the pumps, needed now, is R3.6 million.

Without bricks and other such objects dumped illegally into the sewers, the screws should last at least 15 years, she said.

Meanwhile work is expected to start in 2024 – with 2027 as the target for completion – on a new R350 million inlet system at the Cape Flats sewage plant.

Ms Limberg said the design of the new inlet would consider the installation of mechanical screens upstream of the screw pumps to prevent them being damaged by heavy objects dumped illegally into the sewers.

A specialist would provide the Department of Environmental Affairs and Development Planning with an impact report and rehabilitation plan for Zeekoevlei, she said.