by Christopher Allan, Journalist, Utility Magazine
Sewer rehabilitation – the repair or renewal of an existing sewerage asset – has both short and long-term advantages for sound management of Australia’s wastewater networks. As asset operators continue to leverage the many benefits of sewer rehabilitation, here we consider some of the different projects occurring around the country, revealing how each project draws on a unique technical approach.
Trenchless rehabilitation solutions, such as the relining of aging municipal sewer networks, can dramatically extend the life expectancy of these critical assets, all with minimal above-ground disruptions and service outages during the works period.
Instead of constructing new sewerage assets from scratch, revitalising our current sewer infrastructure can keep project costs down while also meeting sustainability objectives.
Much of Australia’s sewerage infrastructure is deteriorating or nearing end of service life, due to factors like age, historical material selection, and newer demands of urban growth. The traditional excavation approach to sewer pipe repairs is often burdensome on municipal budgets, causing surface disruptions like traffic delays.
Yet without regular monitoring and maintenance, a sewerage system left to deteriorate can become expensive to rescue and introduce new risks like flooding and building damage. Thankfully, new trenchless sewer rehabilitation practices are unlocking longer lifespans for critical sewerage assets around the country.
Whether it’s through the unwinding of a new sewer section built from the latest and most durable plastic, or overseeing refurbishments at manholes and pump stations, water asset operators and government strategists alike are backing sewer rehabilitation to lock-in asset lifespans and reduce risk across the greater network.
Sewer rehabilitation: how it works
The US Water Environment Federation (WEF) describes two classes of techniques in sewer rehabilitation: sewer repair and sewer renewal.
Sewer repair
Sewer repair works are a type of rehabilitation that allows a pipe to realise the end of its useful life. Sewer repairs, often involving location-specific works that seal the sewer pipe, will restore local structural integrity rather than managing the integrity of the entire pipe segment.
The WEF finds that sewer repair techniques include “internal and external joint repairs, sealing joints and cracks, spray lining or applying a coating, and partial replacement”.
Sewer renewal
In contrast, sewer renewal works may extend the useful life of a sewer, securing the integrity of entire pipe segments between manholes. Sewer renewal techniques include “a variety of liners, coatings, panel systems and replacing segments of pipe”.
Many sewer renewal techniques, like the relining of an entire sewer pipe segment with a durable plastic material, have been developed to overcome the material-based challenges of aging concrete sewer pipes, not limited to chemical erosion, cracking and infiltration, and root intrusion.
Some of the most common sewer rehabilitation techniques include:
• A range of sewer relining approaches, such as spiral wound-in-place and cured-in-place lining, which unlock years of new sewer life between two access points
• Sprays and coatings that protect existing asset surfaces from damage and corrosion
• Localised treatments, such as grouting, that target potential hotspots of pipe degradation and infiltration and can often be delivered remotely using CCTV technology
Why sewer rehabilitation?
Given that many sewer rehabilitation techniques, such as relining a section of sewer pipe or undergoing targeted grouting repairs, can be entirely trenchless, water asset operators can minimise almost all above-ground works and service interruptions, saving money and making urban revitalisation projects far more achievable.
Emerging technologies, such as the use of CCTV footage, and new knowledge about the best-practice lining and coating solutions, continues to make trenchless rehabilitation more appealing and affordable.
The benefits of sewer rehabilitation can also extend to positive outcomes for downstream wastewater applications, as asset operators continue to adopt principles of sustainability into Australia’s wastewater.
While sewer rehabilitation remains the smarter choice over sewer replacement in most circumstances, water asset operators and governments will need to complement rehabilitation with new sewer infrastructure, to meet the evolving demands of urban growth.
Indeed, Victorian Government-owned retail water business, Greater Western Water, recently completed works on the new West Werribee Pump Station, a $12 million project that directly responds to service requirements of a key growth corridor in the state.
Sewer rehabilitation projects
Here, we consider a selection of recent sewer rehabilitation projects from around the country that put modern relining and asset refurbishment techniques into practice.
The capital city sewer strategy of Melbourne Water
Melbourne Water coordinates services of Melbourne’s 400km network of pipes and tunnels, and has recently invested $100 million across a four-year sewer rehabilitation program for Victoria’s capital.
The sewer relining and manhole rehabilitation program promised to add a minimum of 50 years of life back to critical assets across Melbourne, a city with some sewerage assets that already date back 120 years.
Between 2018 and 2021, Melbourne Water’s program has delivered upgrades to 15km of ageing pipes across the following eight projects:
• Pascoe Vale sewer
• Maribyrnong River Main sewer
• North Yarra Deviation sewer (Stony Creek Backwash sewer)
• Brighton Main sewer
• Hawthorn Main sewer
• Kew Pumping Station sewer
• Sandringham sewer
• Western Trunk sewer
Five of the projects adopted a spiral wound-in-place sewer relining technique, while two went for cured-in-place relining. In spiral wound-in-place relining, a specialised machine is dropped down a manhole to work on a given segment of the target sewer line, which could be over 100 years old.
The machine unwinds a new PVC liner through the sewer line, expanding the new plastic pipe to the walls of the old sewer, which might be made from concrete or even brick. Once the machine has finished lining the new sewer pipe, grout is often used to fill in any gaps.
The Maribyrnong River Main sewer upgrade, completed ahead of schedule in 2020, used spiral wound-in-place relining to replace a 7.2km stretch of sewer.
Melbourne’s sewerage system is currently valued at over $10 billion, and to steer these critical assets through emerging challenges over the next fifty years, Melbourne Water also delivered its comprehensive Melbourne Sewerage Strategy in 2018.
Future sewer rehabilitation works undertaken by Melbourne Water will include the Epsom Road Main Sewer Renewal project in Kensington, commencing in early 2022, which utilises the cured-in-place lining technique to rehabilitate 1.6km of the sewer.
Local government responses: Fraser Coast (Queensland) and Mount Barker (South Australia)
Critical sewer infrastructure is also monitored and rehabilitated through countless local council initiatives around the country.
Fraser Coast Regional Council
Queensland’s Fraser Coast Regional Council recently announced a $4.25 million investment in sewer relining of a formidable 14.2km of sewers.
With works scheduled for completion by December 2021, the project comes as a response to breaks, cracks, and leaks in the Fraser Coast sewerage network, identified via remotely operated cameras.
Councillor David Lee pointed to the advantages of trenchless sewer rehabilitation via manhole relining in terms of avoiding the cost of digging up and replacing faulty sewer pipes.
“The majority of the work in Hervey Bay is being done in areas near the beach to reduce the amount of salt water entering the pipes through cracks and leaking joints,” said Cr Lee.
“This is particularly important as the salt water affects the ability for treated effluent to be used for the irrigation of cane fields, turf farms and hardwood plantations.”
In this way, the benefits of sewer rehabilitation even extend to positive outcomes for wastewater applications.
Mount Barker District Council
In South Australia, the Mount Barker District Council, who manages the wastewater system of Mount Barker and surrounding townships, recently opened tenders in the latest tranche of their ongoing Manhole Restoration Program.
The program seeks to extend the life of critical wastewater assets including manholes and flushing points, assets that often require monitoring and maintenance from local councils to manage any future costs of substantial repair.
Indeed, a statement from the Mount Barker manhole project raised that failure to conduct regular maintenance work could result in manhole collapse, requiring extensive repairs and even excavation on private properties.
Fortunately, a growing range of coating, lining and surface mortar solutions are available to help asset operators manage the susceptibility of concrete sewerage assets to risks like chemical erosion via sulphuric acid attack.
Trenchless sewer solutions needed now more than ever
In a context of growing federal and state commitments to highly ambitious infrastructure pipelines, emerging technologies will be invaluable to unlock trenchless projects with low-impact construction periods.
The latest techniques of sewer rehabilitation – whether relining an entire section of degrading pipe or even fixing a single crack identified by CCTV footage – will allow the water sector to extend the lifespans of countless critical assets without starting from scratch.
Indeed, with many municipal sewer networks in our major cities being built over 100 years ago, techniques such as wound-in-place or cured-in-place relining will ensure cities avoid expensive crises across sewer networks.
The unwinding of a durable PVC liner within a deteriorating concrete sewer pipe often wins out from a sustainability perspective when compared to digging a new sewer network from scratch, and restoring sewer pipes to optimal condition can even have positive environmental outcomes for sewer water treatment and reuse applications.
