As the operator of the larger main and trunk sewers and treatment plants, Melbourne Water has the responsibility of regularly monitoring and maintaining a large and intricate sewerage system. Their monitoring and maintenance program is carried out to ensure effective performance and safety and includes identifying and fixing structural weaknesses, as well as removing obstacles to flow. City West Water, South East Water and Yarra Valley Water manage customer relations and operate the reticulation system from individual properties and from branch sewers. About 92 per cent of Melbourne’s sewage is treated at two treatment plants; the Western Treatment Plant in Werribee treats about 52 per cent, or 485 million litres a day, and the Eastern Treatment Plant in Bangholme treats about 40 per cent, or 370 million litres a day. Melbourne Water owns and operates both treatment plants.
Using modern technology, Melbourne Water has initiated a long-range CCTV program, operated by Rangedale, to carry out detailed and accurate inspections of their large diameter sewers. The main driver for developing the system were the very long distances between the access chambers. Furthermore, due to saftey concerns of working in confined spaces, robotic inspection was the preferred option.
The project
During the 2009-10 financial year, Rangedale successfully completed CCTV inspection of four different trunk sewers, including;
- The North West Sewer, an 11 km sewer that transfers flow from the Maribyrnong and Moonee Ponds sewerage systems to the Western trunk sewer at Brooklyn;
- The Western trunk sewer – nearly 23 km long and extending from the Brooklyn pumping station to the Western treatment plant;
- The South Eastern sewer is the third and possibly most important sewer to be inspected. As one of the largest sewers in Melbourne, the South Eastern Trunk Sewer is the backbone of the Eastern system, connecting the Kew pumping system to the Eastern Treatment Plant. All the other main sewers in the Eastern system drain into this 30 km sewer, which reaches 4 m at its maximum diameter. It has an average flow of about 350 million litres per day, with the capacity to reach a maximum of 1,700 million litres a day;
- Lastly, the Dandenong Valley Trunk Sewer – a 25.5 km long sewer that transfers flows to the Eastern Treatment Plant is included in Rangedale’s CCTV inspections.
Looking ahead, CCTV inspections scheduled for the 2010-11 financial year include that of the South Eastern Outfall. This is a 56 km pipeline that carries fully treated effluent from the Eastern Treatment Plant to the Mornington Peninsula for release into Bass Strait at Boags Rocks, a very large-scale undertaking.
Unique challenges
In order to effectively manage these critical sewers detailed and accurate sewer inspections are essential.
Like all water utilities, Melbourne Water’s sewerage system relies on the integrity of these critical large diameter pipes to deliver large flow volumes to the treatment plants. These assets range from
1 – 5 m in diameter and are typically between 5 – 76 m deep.
Melbourne Water was looking for a sewer inspection technology that was capable of performing detailed and accurate inspections in large diameter sewers with various flow conditions, while also being able to locate any serious defects, such as cracks. Traditional inspection technology may not detect deficiencies due to the insufficient lighting found in large diameter sewers and/or the fact that the flows inside these sewers are too high for the conventional large diameter sewer CCTV camera systems to function properly.
Solutions
As such, Rangedale devised a Long Range CCTV Unit, to be mounted onto a Hino 4×4 500 Series Truck. The truck was been specially fitted out to house the unit, which consists of a control unit, recording devices including a backup system, and three-phase electric-driven winches and fibre optic rotary joints. There is also a high output three-phase generator to run all electrics whilst the unit is in operation. Up to 3 km of fibre optic cable is used to transfer the digital signal back to the control unit for recording.
The power supply for the lights and camera operation is housed within a float system unit. The unit is fitted out with air conditioning, fridges, a microwave oven and more to enable staff to operate in remote locations. The recharging of all battery operated equipment can be done internally. Also, full wash-down facilities are housed on board to ensure the unit’s sensitive equipment is always kept clean and tidy.
The CCTV camera is mounted on a floating device with four LED lights for illumination in the pipe. Two trailers with hydraulic drums complete the unit and contain up to 3,000 m of 6 mm rope to control the direction and speed of the survey. Man-cages capable of lowering two men into very deep manholes to set up roller systems are existent at the entry and downstream exit manholes.
Benefits
The use of this new technology has been a breakthrough for Melbourne Water. Previous methods of inspection and condition assessment of trunk sewers used man entry techniques, sewer walks and old equipment, due to the limited cable length of standard CCTV equipment and limitations in operating in trunk sewers. Rangedale’s new CCTV system eliminates all OH&S risks whilst conducting sewer walks, providing a long-term benefit by reducing costs associated with backup safety equipment and potential injuries, says Rangedale.
This new sewer inspection technology is capable of performing detailed and accurate inspections in large diameter sewers with various flow conditions. Being able to locate serious defects such as cracks, infiltration, deformations and intrusions that create build-up of debris is greatly beneficial in the repair of pipe.
Furthermore, the sewer video footage is very stable with clear images, which allows the reviewer to make better assessments of deficiencies within the sewer.
The “÷one set up’ capability of the CCTV system is also very useful. The camera can inspect lengths of up to 3 km from one location, reducing the number of setups required, saving time and money as well as minimising disruptions in congested areas.
Conclusion
The project demonstrated that using Rangedale’s long range CCTV system to collect multiple types of data from within a large diameter sewer is an effective inspection method. This was due to its ability to navigate through all types of sewer flows in a stable manner.
The inspected portions of the trunk sewers were found to be in generally good condition. The sewers were considered to be functioning in a satisfactory way and the findings suggested that they will provide adequate service for many years to come.
The valuable sewer data that is gathered can assist asset managers in establishing accurate baselines for future inspections and identifying potential problems, thereby reducing risk of failure.