Saving our sewers

2010-06-23 00:00

ALTHOUGH local residents probably commonly associate closed-circuit television (CCTV) cameras with crime-prevention activities, they can be used in many other applications. This includes inspecting inaccessible locations such as petroleum, water and sewer pipes.

This is exactly what motorised CCTV cameras are currently being used to do in Pietermaritzburg — inspect the city’s aged and over-stressed sewer network.

City sewers have long been recognised as one of the key problem areas contributing to faecal pollution in local­ rivers and streams. This includes sewage leaking out of sewers and storm water getting into sewers, especially after torrential rain storms. This then puts intolerable stress on the already overstretched Darvill wastewater treatment works that featured­ in a front-page story (The Witness, June 21).

According to Brenden Sivparsad, the Msunduzi Municipality’s acting process manager (water and sanitation), who manages the municipality’s water and sewer networks, about 60%, or 900 km, of the sewer system is more than 40 years old. Previous CCTV surveys of the city centre and Imbali indicated that about 20% of the system was defective and needed to be replaced and the municipality has replaced about two kilometres of old or damaged sewer pipes since June 2009. This led to a decision to conduct a CCTV survey of the entire sewer network system.

He said: “CCTV equipment is used internationally for internal inspection of sewers to ascertain the structural integrity of sewer pipelines, which then determines capital refurbishment pro- grammes and funding.”

The R10 million, three-year sewer infrastructure feasibility study of the entire Msunduzi network, including bulk outfalls, is being carried out by Johannesburg-based company Sight Lines Pipe Survey Services. The re-ticulation pipes are made of plastic, vitrified clay and asbestos cement, while the outfalls, or main bulk sewers, are concrete.

Three teams are in the city using motorised CCTV cameras to record and log defects in sewers visually. Structural defects such as broken or cracked pipes, dislodged joints, infiltration sources and root intrusions are located and their exact positions logged, including the severity of the incident. “The system also logs maintenance defects such as blockages, the accumulation of fatty deposits and high silt areas, so that they can then form part of our planned maintenance procedure. Defects like those mentioned contribute to recurring blockages that invariably lead to sewage­ spilling into river systems.

“All CCTV data is electronically captured and presented in geomedia information systems (GIS) format to make it easy to manipulate and examine­,” Sivparsad said.

According to Walter Sutherland of Sight Lines, using its Orpheus camera system the company has surveyed Lincoln Meade and Hayfields and is currently in Scottsville.

“The tractor-mounted cameras are completely sealed, so they are safe from contamination. They travel at a walking pace on a 200-metre-long cable­. We insert them at manholes and survey as far as the cable stretches, before moving to the next manhole to work backwards.” Sight Lines also has a high-pressure water jetting system that it uses to clear blockages, and any debris released is sucked up into a vehicle-mounted tank.

So far, the worst problems the teams have encountered have been blockages caused by tree roots, silt build-up and other obstructions. These are things that should not be in a sewer, but have been inappropriately and incorrectly flushed down a toilet. They include things such as plastic bags and bottles, disposable nappies and rags.

When the teams finish in Scottsville, they will move to inspect sewers in the northern suburbs and outfall sewers, which are the main bulk sewer system.

“These CCTV inspections have a two-fold benefit as they allow us not only to identify sources of infiltration, but they also provide valuable data on the condition of the sewers for asset renewal purposes. The results obtained will be used to motivate for grant funding to repair or replace reticulation and bulk sewer pipes as necesary, depending on the in-situ conditions,” Sivparsad said.

The project is being funded by a municipal infrastructure grant (Mig) of R13 594 500. The contract began in January and it is scheduled to be completed by July 2013. The remainder of the money will be used to implement a hi-tech infiltration monitoring system that is to be incorporated into the municipality’s telemetry systems.

David Still, chairman of the Duzi-Umgeni Conservation Trust (Duct) said that they were delighted that this critically important work had started at last.

He said that although the project funds were approved by national government as far back as June 2007, the award of the tender had twice been held up on technicalities.

LENGTH OF MUNICIPAL SEWER NETWORK: approximately 1 500 km

PUMP STATIONS: 14

LENGTH OF SEWERS INSPECTED: 88,70 km

LENGTH OF PIPE CLEANED: 28,97 km

PROJECT COST: R10 million

CONTRACT PERIOD: three years, from January 2010 to July 2013.

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