The City says this substance, which oozed onto Camps Bay Beach earlier this year, was not harmful, but a sample that was tested was found to contain “significant” traces of aluminium, which is toxic to the marine environment, according to scientist Professor Leslie Petrik.
A sample from a spill of thick, dark liquid on the Blue Flag Camps Bay Beach in March contained "significant" traces of aluminium, which is toxic to the marine environment, according to scientist Professor Leslie Petrik.
The City denied the liquid was hazardous - a position it continues to hold - when it was noticed earlier this year.
At the time, interim mayoral committee member for water and sanitation, Siseko Mbandezi described the substance as "coagulated sediment derived from the tannin-rich water located in the reservoirs on top of Table Mountain National Park" (“Sediment overflow on Blue Flag beach 'embarrassing,” Atlantic Sun, March 23).
However, Mark Jackson, an environmental activist and film-maker, took a sample of the liquid and had it tested at UWC. He has since posted the report online.
The report says the sample was mainly comprised of quartz, most likely due to silt present in the treated water and sand incorporated into the sample during collection.
"The major inorganic elements present in the sample were aluminium, calcium, potassium and iron," the report notes, adding that their presence could be due to coagulant/flocculants, such as aluminium sulphate and sodium aluminate or other water-treatment agents used at the Kloof Nek water treatment facility.
Professor Petrik, the group leader of environmental and nano sciences at UWC who authored the report with Dr Emmanuel Ameh, said: “One can't get confirmation from the City regarding the flocculants that they use to clean the water, and the sludges, with all the rubbish that they take out of the water, are then released either through the stormwater drain or the pipe going to the marine outfall, and apparently this has been going on for many years.
“This is contrary to the permit that they’ve got for discharging into the marine environment, and the sludges contain a lot of aluminium etcetera that’s toxic to the marine environment. The City has not told us what they use as a flocculant and they haven’t told us of the volumes that are being discharged."
Mr Jackson said aluminium sulphate, or alum, was an "environmentally hazardous chemical agent" that had restrictions on its disposal.
"I very much doubt our City even has a licence to dump that sludge, either via our stormwater drains or sewage marine outfall system, directly into our National Marine Park of the Cape Peninsula, of which Camps Bay is part. But I stand to be corrected."
Mayoral committee member for water and sanitation Dr Zahid Badroodien said aluminium sulphate had been in use since 1996 at the Kloof Nek water treatment plant.
“The water treatment process by-product has high (>3000 mg per kg) concentrations of aluminium, calcium, iron and sodium. This is what is expected considering the treatment chemicals used at the Kloof Nek water treatment plant.”
The treatment process at the plant included coagulation, flocculation, sedimentation, filtration and disinfection, he said.
"These processes are optimised and controlled to achieve consistent and reliable performance."
The water-treatment by-product went into the stormwater system and not the sewerage system, he said.
“The coagulation process starts with the addition of sodium aluminate to accelerate the forming of flocculation due to short retention times. Aluminium sulphate is then added to the water, which comes from the dams on top of Table Mountain, as a primary coagulant. Hydrated lime is also added to this water to adjust its pH to achieve optimal colour removal. This is followed by a disinfection step."
Dr Badroodien said the chemicals posed no health risk.
Mr Jackson urged the public to do more to hold officials to account, saying: "Incidents like this show we can easily slide into the whirlpools of degradation currently afflicting other parts of SA if we don't stay vigilant and demand accountability.
“I urge residents and ratepayers to do more. Perhaps the easiest action is join the Camps Bay Ratepayers’ Association and ask them to lay charges next time a toxic residue arrives on our beaches. We all can and must do more."