How to cap a tip

By Catherine Watson

For almost a century, the Wonthaggi tip absorbed household and industrial waste, with “night soil” – the contents of the backyard dunnies – dumped at the back until the town was sewered in the 1970s.

Rubbish dumps are magical places for acquisitive people, including bottle collectors, historians and children. Terri Allen remembers her father loading up the kids for a trip to the tip. They always came home with at least as much as they took, she says, and often more.

But old tips can also be dangerous, potentially releasing methane, contaminated leachate and other pollutants into the environment.

In 2008, several hundred residents of the Brookland Greens Estate in Cranbourne were evacuated after their homes were found to be contaminated with explosive levels of methane from an adjoining old landfill site. 

Understandably governments are nervous about the risks and landfill management and rehabilitation is one of the most heavily regulated procedures in Australia.

Wonthaggi’s landfill closed around 2000. A transfer station now operates at the front of the site, with waste trucked to the shire's sole remaining operational landfill at Grantville.

Bass Coast Shire Council was required to cap the old tip, but the estimated cost of around $23 million was daunting for a rural shire with an annual operating budget of less than $100 million.

Enter Aaron Ferrell, the council's co-ordinator of waste services. This is a man who loves his job. He manages our waste all day, reads about waste management for light relief and will happily talk about it all day, given half a chance.

Wonthaggi is his 15th landfill rehabilitation project, and he knows they can be dangerous places. “I've seen rescue helicopters land on landfill sites to treat injured workers when landfill goes wrong.”

There isn't much wriggle room in this field of work, but Aaron is always looking for better ways of doing things. He became interested in a capping technique increasingly used in the UK, Europe and Japan, which offered the prospect of slashing the bill for the Wonthaggi tip.

Instead of relying on a thick layer of compacted virgin clay to minimise rainwater infiltration into the buried waste, a geocomposite drainage material called Pozidrain is used to channel water away. The material allows the clay layer to be reduced from 1.1 metres to about 300mm. 

That might not sound significant, but across 8.5 hectares it means a huge reduction in the volume of virgin clay required, along with fewer truck movements, less handling and a shorter construction period. 

It also offered a much smaller environmental footprint. Pozidrain is made from a combination of virgin materials and recycled plastic. Topsoil scraped from the site at the start of the project would be blended with mulch manufactured from our own green waste for the final layer.

The challenge was going to be to convince the Environmental Protection Agency (EPA), which oversees landfill rehabilitation in Victoria. The EPA was cautious, but interested. The Wonthaggi project could be a useful case study. 

The technique was not covered by the agency’s guidelines for landfill rehabilitation (last updated in 2015), so months of negotiation followed before it was approved, subject to a raft of provisos and conditions.

Aaron went back to ABG, the UK manufacturer of Pozidrain. Could it meet the EPA's requirements? Yes, came the answer. 

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When the project went to tender, the council chose EcoProject, a Korumburra company, to do the work. It might have seemed an unusual choice because EcoProject had never capped a landfill before. But neither had any other Australian company used this particular process.

Aaron describes EcoProject as a local, innovative company that has helped identify solutions to challenges along the way. The experience, he says, will stand the company in good stead for similar projects in future.

There were other major risks to manage. The council was importing 385 rolls of Pozidrain from the UK. If the material failed to meet the EPA’s specifications on arrival in Australia, the consequences would be dire.

Rather than risk costly delays or compliance issues, the council took the proactive step of funding an EPA-approved construction auditor to travel to the UK and spend nine weeks overseeing production at the manufacturing facility.  This provided an additional layer of quality assurance before it was shipped to Australia.

It proved a wise move. A minor problem was detected in the first few rolls and promptly rectified. The defective rolls were recycled and reprocessed into new rolls, minimising waste and avoiding extra costs.

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With the technical hurdles largely overcome, the project got under way in May 2025. Capping a site this big by the usual method would take up to three years but by Christmas they were running ahead of schedule and expecting to finish by April.  

With any major infrastructure project, there is always another challenge just around the corner. The final layer of capping Wonthaggi’s tip requires 12,500 cubic metres of topsoil/mulch blend spread over the entire site to a depth of 200mm.

The Grantville landfill had been stockpiling mulch for several years specifically for the project. But in February, tests revealed levels of PFAS (per- and polyfluoroalkyl substances, commonly known as “forever chemicals”) marginally above acceptable levels.

The EPA told the council the mulch could not be used on the surface of the capped landfill and would have to go into landfill as priority waste. The estimated cost of complying with that decision was $8 million, taking into account the loss of landfill space at Grantville, the state landfill levy and the cost of buying replacement mulch material.

It was a bitter pill for everyone involved with a project that was designed to save ratepayers millions.

Work came to a halt while Aaron set out to persuade the authorities that there was a better solution. Months of negotiation followed before the EPA agreed to the proposed approach, allowing the project to proceed on condition that the council could demonstrate and effectively manage the risks.

The delay added an estimated $1.4 million and six months to the project, principally through the work needed to repair runoff and erosion damage after a wet winter. The extra costs take the total to $9.4 million, still substantially below the estimated $23 million cost of traditional capping. 

The EcoProject team returned to the site in mid-October ago and it's full steam ahead now. The capping is expected to be finished by the end of the year.

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There aren't many hills in Wonthaggi, so the view from the top of the tip is something of an eye-opener. From here, the landscape opens out across the old rifle range and heathlands, past mobs of kangaroos and the windmills towards the coast. Turn the other way and you look into the Bass hills. 

Closer at hand there’s a hum of action with a small team laying the Pozidrain while a steady stream of semi-trailers delivers the clay to cover it. 

Watching the action, Aaron doesn't hide his pride. Wonthaggi’s tip has been made safer at a fraction of the expected cost – and Bass Coast is at the forefront of demonstrating a new approach to a burden shared by councils across Australia.

The project is being watched closely by the EPA and other councils. he regularly shows visiting colleagues around the site, and has installed a centrally rotating camera so he can keep an eye on his baby. This month he presented a paper on the project at the 2026 Australian Landfill & Transfer Stations Conference.  

He's proud that Bass Coast had the courage to try something different and that – despite the setbacks – a new approach saved local ratepayers around $14 million. 

“I hear a lot of criticism about how councils spend ratepayers’ money. I want our community to hear more of the positive stories too – the work that goes on behind the scenes, the commitment to finding better solutions, and the real savings that can be achieved for ratepayers.”  

The site will be monitored for several years to make sure the system is performing as intended. It can never be built on in the conventional sense, because foundations would penetrate the protective layers or Pozidrain. Trees are out, for the same reason.

Instead, the surface will be planted with kikuyu grass, the bane of gardeners everywhere, but useful here because it forms a dense mat that helps limit water infiltration and prevent erosion.

One day, perhaps, the tip hill could become a park, an astronomical lookout, a skate park, or BMX track. There are plenty of options. For now, the priority is to finish the job.