With 2245km of water mains, 1904km of sewer mains, and 48km of recycled water infrastructure to manage across 16,550 square kilometres in North-Central Victoria, Coliban Water is one of the state’s largest regional urban water corporations. To ensure the continued delivery of safe drinking water and efficient services to its customers, Coliban Water has an ongoing mains cleaning program to help manage its assets.
Manager Assets and Operations at Coliban Water, Steve Dunlop, said cleaning water mains is an integral part of the water corporation’s maintenance program to ensure it is able to continue to meet the Australian Drinking Water Guidelines, as well as assisting to protect the integrity of its water main network and help prevent service issues.
“The cleaning of our sewer network is important to help prevent blockages and improve the efficiency and reliability of our service. Sewer overflows are costly to clean up if they occur inside a home, and pose a significant risk to the environment and waterways.
“We have increased preventative maintenance works to reduce the number of blockages in our network.
“During 2015/16, we spent approximately $200,000 on our water mains cleaning program. Cleaning works were carried out in Bealiba, Boort, Cohuna, Dunolly, Elmore, Junortoun, Laanecoorie, Lockington, Pyramid Hill, Rochester and Tarnagulla.”
Most recently, water mains cleaning was completed in Heathcote in May, and a program of water mains cleaning works for 2017/18 is being planned. The 2017/18 program of works for the inspection and cleaning of sewer mains in Bendigo is underway.
A variety of techniques
There are a number of different techniques that water corporations are able to use to clean water mains. The technique to be used is selected based on site-specific conditions and the identified cleaning objective.
All mains cleaning techniques help improve water quality by removing any deposits, such as grit and debris, that build up over time and can cause the water to become discoloured.
Coliban Water hires contractors to carry out mains cleaning using five techniques, including:
Water mains are flushed if there is a build-up of natural sediments. This can occur after changes in pressure or flow rate after a burst water main. Flushing the main involves opening hydrants to flush the water and any sediment through the mains at high speed.
Air scouring involves forcing a mixture of compressed air and water into the mains. This process also removes any sediment and helps maintains chlorine levels within the water supply network.
Ice pigging involves pushing a thick ice slurry, a mixture of semi-solid ice and water, through the main. The slurry is then removed from a hydrant and collected in a tanker. This method uses minimal water and is environmentally friendly. It reduces risks to the network and there is no need for excavation.
Swabbing involves forcing a large ‘sponge’ through a water main to remove sediment. The sponge is propelled by water pressure, and is removed along with any sediment and debris it collects.
“For sewer main cleaning we utilise a variety of techniques tailored to the condition of the main. The condition of the sewer mains is assessed using CCTV and acoustic sensing technology,” Mr Dunlop said.
The jetting of sewer mains is the most common form of cleaning. Jetting takes place in a section of sewer main between two manholes. It involves pushing a high-pressure hose with a cleaning nozzle through the main against the flow and then pulling it back through.
Jetting is often used prior to inspection or renewals.
Chemical tree root treatment
“Tree roots cause more than 70 per cent of sewer main blockages in our region. Roots searching for nutrients intrude into pipes and catch fats, oils and foreign materials which can reduce the flow and cause blockages,” Mr Dunlop said.
Chemical tree root treatment is a foam herbicide that eliminate roots and prevents further structural damage of the main. Only roots within main pipe and a very short distance outside are affected. Trees and shrubs immediately above ground are not harmed.
Maintaining the mains system
Mr Dunlop said Coliban Water has had good results from its water and sewer mains cleaning program, with further mains cleaning works planned across its service region for 2017/18.
Water main cleaning works take place in autumn and winter out of our spring-summer peak-demand times, while sewer mains cleaning takes place all year round.