An extensive project to refurbish both the Cape Flats 1 and Cape Flats 2 bulk sewer lines has commenced at an estimated cost of R539 million overall, with R133 million budgeted for this financial year alone. A total of 28 kms of pipeline is being rehabilitated, making this the largest project of its kind undertaken in South Africa. Alderman Xanthea Limberg, Mayoral Committee Member for Water and Waste, and Portfolio Committee Chairperson, Alderman Clive Justus, visited one of the five contractors currently working on the line, in Pelican Park, to see how the project is progressing. See the video: https://youtu.be/nQtdhATErrw
| Cape Flats Bulk Sewer System at a glance: A bulk sewer is like a highway for sewage. This kind of pipe carries high volumes from a wide area towards the treatment works. The Cape Flats 1 and 2 bulk sewer system starts at the Bridgetown sewage pump station, from which sewage is pumped up to the Hazel Road mixing chamber, located just south of the Hazel/Klipfontein Roads intersection. From the Hazel Road mixing chamber, the flow is split into the Cape Flats 1 and 2 bulk gravity sewers, made of reinforced concrete, and ranging in diameter from 1000mm to 1800mm. The two sewers follow the same route through the suburbs for an approximate distance of 14km, before discharging into the Cape Flats wastewater treatment works. Construction of the twin CF 1 and CF 2 bulk sewers were completed in 1962 and 1969 respectively. Concrete is vulnerable to damage from the corrosive gases present in sewers, including CH4, H2S and CO2. H2S in particular is aggressive. Plastic is more resistant. The sewers serve more than 300 000 households of the Cape Flats, and the City can transfer flow between them and also the Cape Flats three to allow for maintenance. This makes maintenance easier and lowers the risks of damage to the environment associated with the work. Most of their inflow is from the Raapenberg and Bridgetown pump stations, which service Athlone, Hannover Park, Lotus River, Ottery, Grassy Park, Eagle Park, areas around Pelican Park, among others. |
Work is underway at various sections of the Cape Flats 1 (CF1) bulk sewer line to refurbish the 14 km pipeline, which ranges from 1050mm to 1450mm in diameter – one of Cape Town’s largest sewer systems.
Once the CF1 refurbishment has been completed, work will begin on the adjacent Cape Flats 2 (CF2) bulk sewer, which ranges from 1500mm to 1800mm in diameter. In total 28km of pipeline and approximately 331 manholes will be rehabilitated.
At the Pelican Park section a team, with the help of a 90kg robotic crawler, is currently inspecting the inside of the sewer to determine which sections should be prioritised for refurbishment. A robotic crawler is a remote controlled vehicle that profiles the inside of the pipeline by recording, among other things, the ovality at different points along the way. Ovality refers to deviations from perfectly circular measurements inside the shaft, which in turn tells the engineers the extent to which gases have corroded the inside surface of the pipe. This data is then used to determine the best – most affordable, effective, and efficient – method of refurbishing the different sections of the pipe.
At four meters below ground, and with a range of corrosive gases that are present in sewers, the work can be dangerous and requires careful and precise handling.
Once positioned by an intensively trained team member, the robotic crawler travels along the base of the pipeline, recording footage and measurements and transmitting diagnostic data by means of a laser beam to the processing system, visible on monitors in a specialised van above ground.
600 tons of foreign objects removed
Before this aspect of the work could commence, the sewage flowing through the line had to be diverted to the larger adjacent CF 2 line, allowing the teams to clean the system of built up materials.
During four months of cleaning this section of about 2km, more than 600 tons of rags, silt, sand, grease, bricks, cutlery, animal carcasses and more were removed. All of these are illegal to dispose in sewers, and contribute to blockages and overflows that damage the health of our communities.
Once the inspections have been completed and the relative corrosion of different points of the line are known, structural rehabilitation of the now-clean pipe can begin.
Trenchless Technology
Innovative technology will again play a central role at this stage of the project. There are three overarching methods of Trenchless Technology – namely, Cured In Place Pipe (CIPP) lining, Calcium Aluminate Cement (CAC) and Spirally Wound Liner (SWL) – and each will be considered when deciding on the best rehabilitative solution for different sections of the pipeline.
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Trenchless Technology refurbishment means there will be no lengthy and disruptive excavations while work is underway. This means residents and businesses will not be inconvenienced by invasive construction sites in the area, and the only visible signs that maintenance work is being carried will be in the form of some staff and vehicles at manhole access points. This method is also approximately three times more cost effective than conventional excavation construction work.
Project made possible by construction of Cape Flats 3
A few years ago the City created redundancy in the Cape Flats bulk sewer system by constructing a new bulk sewer – Cape Flats 3 (CP 3), using the latest advances in protective polyurethane lining systems.
Construction of CF 3, completed in 2017, created sufficient additional capacity to allow a cleaning and rehabilitation project of this scale and intensity to proceed. With the support of CF 3, the flow through either CF 1 or CF 2 can be shut off completely, without requiring costly and disruptive overpumping to keep sewage moving. In short, without the existence of CF 3, this project would not have been possible. The scale of this work combined shows the City’s commitment to reducing sewer overflows in the Cape Flats area.
Investing into key infrastructure
‘Our pipe refurbishment and replacement schedule is determined by a Master Plan, which tracks the relative age and performance of the entire network across the city. This sewer system was identified for proactive maintenance not just because of its age, but also the vast area it services.’
‘The overall project is currently subdivided into five projects that the City is managing internally. Each project has a budget of R40 million, and the City has dedicated approximately R123 million to the CF 1 refurbishment for this financial year alone.
‘Proactive maintenance work is critical to ensuring the system operates optimally and continues to service residents and businesses now and in the future. It’s exciting to see how the latest technology and materials available today are being used to strengthen the existing system, significantly extending its lifespan. It is in a sense groundbreaking, without having to break any ground,’ said the City’s Mayoral Committee Member for Water and Waste, Alderman Xanthea Limberg.
