General

City unpacks short-term interventions to help tackle pollution at Milnerton Lagoon

The City of Cape Town hosted its second quarterly report-back meeting last night, Wednesday 30 November, with community members who live around the Milnerton Lagoon. Residents were introduced to a team of expert consultants appointed to formulate an action plan of short-term solutions to water quality in the lagoon. Updates were provided on current pollution mitigation measures, including litter trap installations. In the coming years, the City aims to restore the lagoon environment via multi-billion rand sewerage and stormwater infrastructure upgrades coupled with on-the-ground pollution mitigation measures. The aim is to steadily close off pollution sources to the lagoon over time, building up to the ultimate goal of dredging the water body and removing the sediment containing decades-long build-up of pollution.

At the Quarterly Stakeholder Engagement Meeting, the City presented feedback on actions to help improve the inland water quality of the Milnerton Lagoon through short-, medium- and long-term solutions.

‘The team of external scientists and experts appointed by the City to devise the remediation plan were at the meeting to present an update on their work. This was an opportunity for the community and stakeholders to engage directly with this expert team.

‘The Milnerton Lagoon’s ecological condition is poor due to multiple pollution sources and requires the intervention of various stakeholders, from government, to the public and industries within the Diep River Catchment area. The City aims to steadily close off pollution sources to the lagoon, so that we can dredge and remove the sediment at the bottom, along with decades of pollution build-up. We are committed to addressing these challenges in partnership with all who care about restoring the health of the lagoon environment, which is non-negotiable for the City,’ said the City’s Mayoral Committee Member for Spatial Planning and Environment, Alderman Eddie Andrews.

Consultants shared several possible short-term measures to improve the lagoon quality, which will be explored in detail in coming months. These measures include aerating the lagoon to introduce healthier oxygen levels, as well as potential bio-remediation solutions. Other short-term measures include improving the functioning at Potsdam, and exploring extra package plant capacity technologies at this facility.

Consultants will also thoroughly explore the process required to dredge the lagoon within three to five years to remove decades long pollution build-up.
What the public had to say on the Milnerton Lagoon challenges

To ensure the expert consultants take community feedback into account, the City invited residents to comment on the Milnerton Lagoon on 29 October 2022, and 31 written submissions were received by the closing date of 9 November 2022.

The department will supply the environmental consultants with the comments for their consideration when drafting the remedial plan for Milnerton Lagoon. The submissions from the public were summarised as below:

Changing the Milky Way Detention Pond into a Retention Pond
Building community ablution blocks in informal areas
Diverting stormwater channels away from the river
Installing renewable energy solutions at pump stations around the Milnerton Lagoon, preventing the impact of load-shedding
Community partnerships and innovative ways of removing solid waste from the Lagoon
Widening the mouth of the Lagoon
Turning waste discharged into energy
Bio-remediation
The public can still submit comments to the following email address: Enviro@capetown.gov.za

Short-term solutions at different stages of implementation

At the previous community meeting on 6 September 2022, residents supported the medium and long-term interventions and requested more short-term solutions. The Water and Sanitation Directorate implemented various interventions to reduce pollution reaching the fragile ecosystem.

SHORT-TERM ACTION BY WHEN
Quarterly stakeholder engagements In place (September 2022)
Ensure all pump stations in this catchment have a sewage spill response protocol
Three site specific sewage spill protocols in place since February 2022 at the critical pump stations in this catchment (ie Koeberg, Sanddrift and Table View East).

Generic Protocol in place for other pump stations.

Establish Milnerton Lagoon Remediation Task Team In place (November 2022)
Complete feasibility of low-flow diversion at Erica Road, including a new trash track at the top of Milky Way Completed (November 2022)
Improve operations at Koeberg pump station

(There is a permanent generator on site which operates during load-shedding. The mobile pump temporarily helps manage the flow of sewage into the pump station, supplementing the capacity of two pumps, while the valve replacement project is underway and should be completed end of December.)

In place (October 2022)
Litter nets on stormwater outfalls Installing (November 2022)
Establishing a catchment pollution response team In process (November 2022)
Trial bio-remediation In process (December 2022)
Feedback on Temporary Package Plant feasibility at Potsdam Wastewater Treatment Works (WWTW) Due December 2022
Opening of the estuary mouth As needed

‘Everyone – from all spheres of government, to industries and residents – who live in the vicinity of the Diep River Catchment need to come together to tackle and reduce the chronic pollution entering at various points along this water body, which eventually ends up in the Milnerton Lagoon.

‘In addition to the short-term interventions, the Water and Sanitation Directorate has also placed sandbags at the Erica Road Outfall, benefiting the Lagoon and Potsdam by reducing pollution that reaches the waterbody and limiting the amount of lagoon water pumped to Potsdam WWTW for treatment. It also aims to create a coffer dam to pump polluted stormwater into the sewer network for treatment at the Potsdam WWTW.

‘The directorate is also concluding the bioremediation Request For Information process that will help the City understand the effectiveness of using bio-enzymes to remediate sewer spills and ambient water. We are committed to cleaning up the Lagoon by stopping pollution at its sources, which includes better equipping Potsdam WWTW so that the treated effluent is of better quality,’ said Councillor Siseko Mbandezi, the City’s Acting Mayoral Committee Member for Water and Sanitation.

Lagoon odour

‘The Milnerton Lagoon goes through cycles of releasing hydrogen sulphide, causing a smell that impacts the community negatively. The City is investigating various short-term solutions to determine their potential to address water quality and odour around the lagoon,’ said Councillor Mbandezi.

We have determined that the sulphur smell originates from the excessive accumulation of particulate organic matter in sediment that has caused bacteria to proliferate to such a degree that they are using oxygen at a rate faster than it is resupplied. This causes sulphate-reducing bacteria to switch from aerobic to anaerobic respiration, that ultimately generates the hydrogen sulphide.

To fix the smell, we need to control the source of the particulate organic matter and introduce oxygen-rich water to the Lagoon. The particulate organic matter that leads to these situations is often from wastewater, treated and untreated.

Potsdam WWTW

Potsdam WWTW is an ageing facility, requiring a capacity and technology upgrade valued at R5 billion and ongoing maintenance and remedial work. The City has invested heavily in the operational maintenance of the facility through the refurbishment of the Primary Settlement Tanks, inlet sump and reinforcing reed bed 1. The City is steadily working towards upgrading Potsdam, which is also on the Mayoral Priority Programme.

Source: City Of Cape Town