Routine wastewater rehabilitation often uncovers complex challenges that push teams to innovate. By rethinking standard approaches, together with SA Water, Interflow transformed a challenging sewer renewal project into a safer, cost-effective solution that shows how everyday maintenance can drive major advances in water sector safety.
During Ozwater’25, Interflow won the national Water Industry Safety Excellence award (sponsored by the Water Services Association of Australia) at the Australian Water Awards, an accolade recognising outstanding initiatives and team contributions in considering and playing an active part in the area of safety improvement and injury prevention across the entire water industry.
Interflow rehabilitated eight sewer lines using a custom technology and process called Midline Expansion, eliminating the need to build eight new access chambers. The innovative spiral-wound lining approach reduced the safety risks posed to workers and the community from excavation in high traffic areas and multiple confined space entries.
Know of an outstanding water project? Nominations for state and territory awards are now open.
Interflow’s Peter Button said the innovation was born of a particularly tricky trenchless rehabilitation challenge.
“Interflow currently has a multi-year framework with SA Water for wastewater network rehabilitation, including renewing wastewater pipes. What made this project different to the regular trunks package work we do was the length of the lines,” he said.
“Normally, adjacent access chambers are spaced about 50 to 200 metres apart. But this project had lengths up to around 350 metres. Furthermore, this project ran underneath Salisbury Highway in Adelaide’s north, carrying over 50,000 vehicles a day, so work was scheduled at night.
“We chose a spiral-wound technology, allowing us to reline a pipe with live flow – removing the need for bypassing. However, there are limits to how far you can go from one access chamber to another, depending on pipe diameter. For 525mm and 600mm, the limit is about 200 metres. Some of our lines were over 300 metres.”
Button said that, as with any lining system, access is required at one end to insert the liner and another access point to finish the process: “In this instance, we needed to do that halfway along a pipe – underground – without access from the surface.”
“In the past, we’d either build a new access chamber in the middle – splitting a 300-metre line into two 150-metre ones – or drill a temporary hole down from the surface. But neither was an option this time due to depth and groundwater levels,” he said.
“Opening up an excavation would cause groundwater to flow into the sewer system, and creating an access chamber on such a busy road would require lane closures – it just wasn’t feasible.
“So that was our challenge: how to complete the lining process, particularly locking off the end, without surface access.”
The challenge of pinning the liner inside the pipe without anyone being physically present set Interflow off on a series of trials and errors, with the effective solution utilising hydraulics.
"The innovation involved hydraulic cylinder heads mounted on the end of a trolley that we fabricated to fit onto our existing camera systems. We drove the camera up from the other end, positioned it halfway, and used hydraulics to actuate the cylinders – pinning the liner in place,” Button said.
“That’s the simple explanation, but it took about 25 iterations to get there. We needed visibility, so it had to integrate with the camera system. Only the third design attempt actually worked.
“We also had challenges like cable weight. The hydraulic cables dragged heavily and burned-out our camera motors. We tried four different cable types and experimented with flotation. We even strapped pool noodles to the cable to help it float on the flow – that only lasted one round before it created more problems. But it was worth a try.
“When we began exploring options, our Engineering Solutions team had developed a prototype a few years back in a simpler scenario – shorter lines, only about 50 metres, using hand-pumped hydraulics.
“So the concept of using hydraulics had existed within Interflow, but making it work for this particular challenge was entirely new. But we got there in the end.”
Button said finding trenchless solutions that reduce or remove the need for human access to underground assets will always help to create safer work processes and systems.
“Excavating access chambers in the middle of busy highways is inherently risky. You’re dealing with open excavations that usually can’t be completed in a single shift. We would’ve needed to construct about eight new access chambers over six to eight weeks,” he said.
“It’s also more difficult working in open excavations with trench boxes compared to existing chambers with height safety gear. Fatigue is another factor. It’s harder for crews to manage new, complex access setups.
“Our Adelaide team has been part of four or five tender planning discussions since, exploring how we might apply midline expansion elsewhere. One upcoming project will use the same method, which wouldn’t have been possible a few years ago.”
The project was also a success from a partnership perspective, as the final solution ended up being more cost-effective than a traditional approach, with the benefit of that cost saving continuing into the future.
"Our framework with SA Water is a TOC (target outturn cost) contract. We price a job, and if we deliver under budget, we share the profit. If we go over, SA Water shares the overrun. So there’s real incentive to innovate, it benefits both sides,” Button said.
“Originally, we priced this job based on constructing new access chambers because, at the time, that was the only way. But during kickoff meetings, we started looking at groundwater and stakeholder challenges, and that’s where the idea was born.
“The potential upside was huge and it worked. We saved around half a million dollars, which allows SA Water to reinvest in other infrastructure projects.”
Winning the award was recognition of a lot of hard work and patience, Button said.
"It was great for the team to be recognised on a national level. We’ve had sessions since to reflect on the achievement. If we don’t pause to celebrate successes like this, they can pass by unnoticed,” he said.
“Our Engineering Solutions team put in a lot of hours that aren’t always visible, so this award really highlighted their behind-the-scenes contributions. It helped put them in the spotlight.”
Know of an outstanding water project? Nominations for state and territory awards are now open.