Building a new community on a former quarry and landfill is no mean feat. But real estate developer Riverlee and a team of engineers have managed to pull it off.
The $2 billion New Epping development, 18 kilometres from Melbourne’s CBD, is designed to be a “city within a suburb”, complete with residential neighbourhoods, commercial spaces and a health, wellness and knowledge precinct.
Spanning 51 hectares, the development will provide housing, employment and commercial opportunities to the north Melbourne suburb – revitalising a twice-used site that may otherwise have lain dormant.
“This is a true urban renewal and regeneration story,” David Lee, Development Director at Riverlee, said.
“It will drastically improve the local environment while also creating a community that will redefine the area in terms of urban experience and wellness. New Epping will set a new standard in how we regenerate infill sites and integrate mixed-use sites into the broader community.”
Two of the mixed-use project’s 30 buildings are now complete, but the end results didn’t come easy.
The engineers involved in the project sat down with create to discuss how they navigated hurdles on a challenging site and the ongoing benefits of urban regeneration.
A dilapidated site
When Helia EHS General Manager Jeremy Newstead was engaged by Riverlee to assess the land chosen for the New Epping site, he found it completely derelict.
One of the former basalt quarry’s holes had operated as a landfill and was filled to surface level with general rubbish, reaching up to 18 metres in depth at some points.
“While today’s landfills are a lot more heavily engineered, fully lined with gas and leachate collection systems, the old landfill contained waste directly connected to the earth beneath the rock,” he said.
Sitting on top of the former landfill was a 2–4 metre clay cap covered with grassy vegetation. “Some of the site’s other quarry holes also had open water features or housed residual equipment associated with the former landfill,” Newstead said.
To get the site up to scratch in terms of safety and stability, there were several issues to overcome, including geotechnical challenges due to the ‘“uncontrolled fill” in the landfill.
“If you’re going to place pressure on top of a landfill, such as a building, this can cause issues with differential settlement,” Newstead said.
Given there is a very large landmass of buried waste on the site, the team had to contend with environmental issues, including leachate that potentially contaminated the natural groundwater and surrounding surface waters.
Landfills are also dynamic in nature in terms of gas generation, said Core Environmental Projects Technical Director James Lucas, who consulted on the building gas protection and interception design in Stage 1 of New Epping.
When landfill gases such as methane or carbon dioxide are disturbed, they can be released, posing potential health hazards to people in the buildings above.
“One of the key challenges has been continuously monitoring the gas regime, and responding if we see any changes,” Lucas said. “Very early on, the developer set space aside for ongoing gas management infrastructure.”
Construction of the buildings’ gas protection onsite has been challenging, particularly with the impact of settlement, which can create strain on the gas protection installed underneath the buildings, needing to be considered.
“We’ve had to find safe venting locations for the systems and coordinate all this infrastructure with service engineers, civil engineers and structural engineers,” Lucas said.
For the first building, the structural engineers originally wanted to build a band beam slab, which had to be completely redesigned to accommodate the gas venting system.
“There’s been a learning piece for a lot of the engineers who haven’t worked on sites that need gas protection before, with coordination required from the outset,” he said.
To overcome the geotechnical challenges, the buildings constructed on top of the waste were piled down to the basalt solid rock and fastened by a slab, mitigating any opportunity for settlement.
Tackling the environmental issues required rigorous assessment to test the soil, groundwater, leachate and creek banks.
“We implemented some leachate groundwater pumping systems to manage any migration of contamination,” Newstead said.
To mitigate the impact of landfill gases, the team developed three lines of defence, with venting, a robust gas membrane and structural elements.
“We designed a venting system, followed by a gas membrane and a slab on top,” Lucas said.
The venting system is passive, minimising ongoing maintenance and energy costs for the building owner, which is driven by whirlybirds to collect any gas surfacing from the ground and then diluted under the membrane.
“Eventually, all the mixed diluted gas ends up venting at a concentration well below any level of concern in a safe space on the building rooftops,” he said.
The inlets positioned around the perimeter of the buildings have been coordinated to let air in, with the locations of the vent pipes strategically chosen, travelling up through dedicated venting shafts in the building.
“Given the amount of gas underneath the buildings, we wanted to double check the passive venting system would be enough, so we examined thermal buoyancy and wind effects on several venting layouts using computational fluid dynamic modelling to optimise the venting system on the first building,” Lucas said.
“The total venting volume was also designed to account for any downtime in the passive system, for example in low wind conditions, so the concentrations of gas remain within safe levels.”
Quality assurance, verification and monitoring
To ensure the buildings were safe to inhabit, quality assurance, verification and monitoring have been conducted at each step along the way.
During construction, an independent inspector supervised the installation of the venting system to ensure it conformed with the design.
“The independent inspector then verified the manufacturer’s quality assurance and installation of the gas membrane,” Lucas added.
Once the slabs were poured, the venting system was also verified to check the gas concentrations were at safe levels.
Monitoring the New Epping site is a continuous process which includes detecting changes in the groundwater onsite and offsite, rectified with pump-and-treat groundwater remediation.
“There were several rounds of gas monitoring conducted under the building to make sure the levels were safe before occupation,” Lucas said.
“We also have crews out there as different work is conducted, because there can be risks when the cap is pierced or gas builds up in the structures, so workers are equipped with personal gas-detection monitors,” Newstead added.
The benefits of large-scale revitalisation
On a high-level scale, the project is driving sustainability through reuse of the old quarry and landfill.
Before the restoration, Edgar’s Creek, which runs through the site, was in disrepair, plagued by overgrown weeds.
“Now, the creek has been revitalised, with a new habitat built for the growling grass frog,” Newstead said. “We’ve also been able to improve the groundwater quality through onsite soil remediation.”
There are also various social benefits that come from repurposing the space, including the development of a new health precinct in the area.
“There are so many benefits for the surrounding residents, including an increase in land value and a connection to Edgar’s Creek Corridor which was previously inaccessible,” Newstead said.
Without the New Epping development, the site would have likely remained derelict or transformed into yet another golf course.
“Often these landfills are neglected,” Lucas said. “But through the environmental investigation, assessment and remediation that’s required for development – it’s actually rehabilitating the land.”