Special commendation ‒ Water Care: Duikersvlei Project
It is often easy to pack up and leave, without thinking about what happens afterwards. Pollution, water contamination and waste are unwelcome cousins many companies cannot get away from quickly enough. The community left behind has to deal with the fallout.
But AECI Limited have refused to pass the buck. For more than 30 years, the Kynoch Milnerton site in Cape Town has been used to produce ammonium nitrate fertiliser. During the phased closure of the site, which until recently belonged to AECI , its soil and groundwater were found to be substantially contaminated with ammonium nitrate, with some localised areas of groundwater containing 1% of nitrogen as ammonium nitrate.
The Duikersvlei stream, which crosses the site, was affected, as was the interconnected Reitvlei wetland system, specifically the Milnerton lagoon with nitrogen concentrations as high as 900mg of nitrogen per litre (N/l). Initial steps to reduce the amounts of nitrogen included the removal of dumps and contaminated soil, general maintenance of the stream and fitting a cut-off barrier at the toe of the embankment to stave off the contaminated groundwater.
This move led to the first signi-ficant reduction of nitrogen levels in the river, which registered at 100-200mg N/l. Although it was a significant improvement, the levels were still too high from an eco-logical standpoint.
Explaining the effect that the nitrogen had on the river, Martin Burr, director of AECI, said: “It was causing eutrophication, which means there were way too many nutrients in the water and it was killing all the vegetation. There was basically no birdlife and no aquatic life in the river.”
Eutrophication promotes the proliferation of weeds, which fight the survival of indigenous vegetation.
In 2005 AECI began planning extra measures to reroute the stream to avoid the segment contaminated with nitrogen. Subsurface drains and a water resistant barrier were designed to extract the tainted groundwater and prevent further contamination.
After an environmental impact assessment was done and the green light was given by the Western Cape’s department of environmental affairs and development planning, work began on the project in May lat year, with half a million tons of soil removed by October 2006. The project’s design incorporated drop-down gabions and bed-erosion resistance to reduce flow velocities and to account for stream meandering requirements.
The project was an overwhelming success, with nitrogen prevalence levels being reduced to 10mg N/l beyond the targeted levels of 15mg N/l. “Part of the project involved revegetation of the stream, replacing alien plants with indigenous ones,” said Burr. “All the typha and the kikuyu have been removed and we are continuing to manage that process every season. Birdlife has returned to the river and it is quite abundant.”
Burr said the project was not feasible during the company’s operations in the area because there was an effluent dam on the site, on which it relied to dispose waste material. The rerouting of the Duikersvlei stream cost the company about R12-million.
The company’s Milnerton site in Cape Town was developed as a fertiliser factory in 1965. AECI began closing its operations on the site in 1999, with the last plant being closed in 2004. The site was leased out to film companies, but has now been bought by a developer.