Scientific Tests Confirm Water Quality at Zandvlei

Scientific tests conducted by the City of Cape Town after the recent sewage spills into the Zandvlei nature reserve in Muizenberg have confirmed that the water quality of the vlei is acceptable.

On 19 and 28 September 2007, a malfunction at the Sand River pump station caused sewage overflows into the Langevlei Canal, which in turn feeds into the Zandvlei Nature Reserve.

However according to Sipho Mosai, Director: Water Services, tests conducted by the City's Scientific Services Branch after the overflows confirmed that the water quality of the Zandvlei was still within the national guidelines for freshwater bodies.

"Bacteriological tests of vlei water conducted on 20 September registered 240 faecal coliforms per 100 ml, and 180 e-coli per 100 ml. This is far below the allowable limit for water sport actvities of 1 000 faecal coliforms per 100 ml and did not indicate any cause for alarm.

"A test on 27 September and subsequent tests also did not indicate any noticeable deterioration of water quality. The public can rest assured that we will continue to monitor the water quality," says Mosai.

According to Mosai the mechanical and communications problems which caused the spills, have been rectified.

"The Sand River pump station is equipped with a duty pump and a standby pump. When one of the pumps malfunctions, it is removed and sent away for repairs. The standby pump then takes over. It is at times like these that the pump station is at increased risk for the duration of the repair.

"On 19 September the mechanical seal on the duty pump broke and the pump was removed for repairs. From 19 September to 1 October, the pump station was operating on its standby pumpset. Unfortunately rags entering the pump station caused the standby pump to trip, resulting in the overflows.

"In addition, the telemetry unit which communicates alarm data to the Schaapkraal control centre was delayed by increased radio traffic due to band restructuring. Pumpset failure signals were not transmitted, thereby delaying the mobilisation of response teams.

"To prevent this from recurring, a new radio repeater will be installed at the Steenbras Water Treatment Plant and telemetry upgrades for the 26 pump stations in this area are due for completion by November 2007.

"Nonetheless, Zandvlei's nature conservation officers raised the alarm of the spillage and immediately informed the City's Scientific Services Branch on both occasions.

"Shortly after the incidents, inspections of the Langevlei canal showed no visible sign of sewage in the water as this had already dissipated. The bottom of the canal was clearly visible and the level of indicator bacteria was within the recommended guidelines for freshwater recreational water.

"In order to treat the water body, the bio-augmentation service provider has to visually see the extent of the pollution. Results of water analyses confirmed that that there were no indications that costly bio-augmentation was necessary," says Mosai.

During 2006, unprecedented Eskom power outages affected almost all of the City's sewage pump stations across the Metropole, resulting in sewage pump station overflows.

"Subsequently, high risk pump stations were identified and standby generators were installed at critical stations, such as the Sand River pump station.

"However, generators are only a safeguard against external electrical power failures. The recent malfunctions were caused by mechanical problems so the generator had nothing to do with securing pump station functionality," he said.

Issued by:

Communication
City of Cape Town
Tel: 021 400 2201

Media Queries:
Sipho Mosai
Director: Water Services
Tel: 021 400 5983
Cell 084 780 1638