Zeekoevlei pollution now mostly contained following non-stop mitigation efforts

22 July 2021

The City of Cape Town has received the pre-directive issued by the Western Cape Government’s Department of Environmental Affairs and Development Planning regarding the pollution at Zeekoevlei and confirms that the health of waterways is of top priority for the City. Over the past two weeks, City officials have been working tirelessly, including through the night, to minimise the environmental impact of sewer overflow into Zeekoevlei, part of the False Bay Nature Reserve.

The spill is the result of infrastructure damage due to illegal dumping into the sewer system, significant stormwater ingress and the damaged manholes. A further contributing factor was the malfunction of a screw pump at the inlet works. The spill has been mostly contained and seepage into the vlei significantly reduced – largely through diversion into the wastewater pond system.

A draft action plan has been compiled to address the rehabilitation and repair required, including for the infrastructure of the roads and picnic area, the terrestrial ecosystem and banks of the vlei, as well as the water body. A consultant will be appointed to assist with a detailed plan. Some urgent superficial cleaning of the banks is already taking place.

Efforts to date include:

Sandbags being placed around overflowing manholes to mitigate and divert the flow from entering the Zeekoevlei.

Repair of damaged inlet infrastructure. Two screw pumps are now available at the damaged inlet works to the Cape Flats Waste Water Treatment Works (WWTW). One screw pump is already in operation following a gearbox installation, and the other is being worked on.

For context, three of the four permanent screw pumps previously experienced gearbox failure, with damage caused by bulky objects dumped into the sewer system, such as gas canisters, as well as wear and tear. The screws were replaced in 2018, and without the illegal dumping of items such as bricks into the sewer system, the screws should ordinarily last for at least 15 years.

The City has been using a number of temporary pumps to get sewage into the treatment works while permanent screw pumps are in for repairs. The design of the WWTW inlet pre-empts an eventuality of screw pump malfunction by means of an overflow weir, to discharge incoming flow into an adjacent pond. This overflow would not impact on Zeekoevlei and would be contained within the ponds of WWTW. Functioning screw pumps will enable the sewer levels in the Cape Flats pipelines in the vicinity of Zeekoevlei to be drawn down.

The effects of screw pump malfunction alone would have been minimal, but the added factors of damaged manholes and major stormwater ingress meant that design contingencies were insufficient to contain the spillage.

Recent heavy rains have also contributed to stormwater ingress into the plant.

Additional temporary pumps have been sourced to divert sewage away from the vlei as far as possible. These are being monitored closely in case of high rainfall.
Identifying and repairing manholes that have been damaged which likely contributed significantly to the sewer overflows. Going forward, these manholes will need to be redesigned and built higher above the ground.

The City is further set to commence with the planning and design of an upgraded inlet works for the Cape Flats Wastewater Treatment Plant at an estimated cost of R 350 million.

The draft action plan (mentioned above) sets out steps starting immediately, through to April 2022. Immediate rehabilitation steps include clearing of sludge, sand, litter and debris from the access road, paved side road and picnic sites; reinstatement and repair of brick paving; repair of tarred access road where subsidence has occurred; removal of a one metre edge of sludge, vegetation and litter; and removal of litter washed in due to sewage flow, as well as bank shaping and revegetation. Attention to the water body is critical and an upgrade of the main Zeekoevlei weir will be looked at to assist in improving the water quality and removing sediment, which will mitigate the inflow and accumulation of sewage.

The City will continue to engage with stakeholders, including provincial government, on the progress of this matter and to find ways to address concerns holistically.

In the meantime, residents are reminded that sewers should only be used to dispose of human waste, toilet paper and grey water. The City asks residents to please help spread awareness throughout their communities.

End

Published by:
City of Cape Town, Media Office