“Technological innovation, the input of highly specialised multidisciplinary services and effective collaboration between different teams led to a solution that embraces the client’s needs as well as the community’s needs. The solution ensures that raw sewage is safely conveyed to the Macassar WWTW for further treatment without endangering the surrounding communities, all while extending the life of the City of Cape Town’s current infrastructure for many years and providing the City with new state of the art infrastructure,” Claude Visagie, Aurecon Associate - Water and Wastewater Engineer.
The Black-Mac (Blackheath – Macassar) bulk sewer was constructed in 1983. Its catchment consists of Blackheath, portions of Blue Downs, Croydon and portions of Macassar in Cape Town. Wastewater collected from the high-density residential areas in Cape Town passes through the Black-Mac screening station, down large sewers (7,3 km in length) and underneath the Eerste River siphon, before entering the large and deep Macassar pump station that pumps it to the Macassar wastewater treatment works (WWTW) for further treatment.
Over time, vandalism, theft, corrosion, lack of maintenance and overloading rendered the sewers in a state of disrepair, the screening station defunct, and the pump station barely operational.
Aurecon was appointed by the City of Cape Town to address these issues as consulting engineers on the project. Our project leaders assembled a dynamic multidisciplinary team to design and manage the reconstruction and refurbishment of the screening station and pump station, as well as the rehabilitation of the conveying sewers.
The project faced several technical challenges, was adjacent to ecologically sensitive wetlands and had the requirement to complete the refurbishment and rehabilitation activities without disrupting operation of the system. The system was kept operational by installing a bypass pumping system that intercepted sewage from upstream manholes and pumped it into the downstream rising mains, effectively isolating the pump station and the equipment from any inflows.
To overcome the challenge of the close proximity of the infrastructure to ecologically-sensitive wetlands, environmental consultants were employed to advise on the placement of a new pipeline to minimise the environmental impact of the construction activities. One of the pipelines runs 7-9 m deep through a nearby suburb, posing a safety hazard to the community during construction. The project team effectively managed this by hosting workshops with the community throughout the project, and involving the police and authorities to help raise awareness of the dangers related to the works.
The Black-Mac screening station and Macassar pump station were successfully commissioned on time in September 2017 and are currently operating efficiently. The 3.5 km section of 800 mm diameter pipeline between the screening station and Eerste River siphon was completed early in January 2018. A completely new 3.8 km 900-1 200 mm diameter concrete sewer pipe is currently being installed from the Eerste River siphon to the Macassar pump station to replace the existing structurally deteriorated sewer, and is on track for completion by August 2018.
The project was designed to the highest standard, with a strong focus on creating infrastructure that is vandalism, theft- and future-proof. The current completed and recommissioned infrastructure is unrecognisable from its former dilapidated state, and boasts state-of-the-art equipment controlled from a remote centralised station. Novel technologies were required to restore the infrastructure and install new equipment in a safe manner, all while accommodating existing flows.
“The Black-Mac screening station and Macassar pump station represents a prime example of Aurecon’s multidisciplinary capability and how effective communication, experience and collaboration between all stakeholders, including the client, contractors and the community, can easily and quickly resolve challenges to ensure timeous delivery,” said Visagie.