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There is no secret that the smell from a landfill stinks. But the real concern is what is beneath the surface.
At Tamala Park Waste Facility, situated in Perth’s northern suburbs, the answer to that is leachate, and a lot of it.
Tamala Park landfill is run by the Mindarie Regional Council and has accepted the household waste of 800,000 Perth homes for 35 years.
The council is made up of seven local governments and was due to reach the end of its operational life around 2028, however, an excessive buildup of liquid waste is now threatening to derail those closure plans.
As of October 2024, data shows there were 167 olympic sized swimming pools worth of leachate accumulated at the bottom of the tip. Without any removal methods in place, that number is expected to have risen.
The situation has now triggered formal regulatory enforcement. Western Australia’s Department of Water and Environmental Regulation issued the regional council an official Environmental Protection Notice on August 3.
The notice requires the MRC to provide a detailed and accurate determination of the leachate levels as well as a leachate removal plan, and they have 30 days to do it.
The EPN also requires the council to improve its landfill gas management, provide updated landfill closure planning, and undertake additional technical investigations.
Western Sydney University science professor Ian Wright has been a water scientist for 30 years and describes leachate as the liquid often seen at the bottom of household bins.
“Leachate is the liquid that builds up in rotting rubbish. So a lot of people might have seen it if your garbage bin with lots of food and kitchen scraps has been left in the house, and you perhaps went away for a few days,” he said.
“It’s often a tea-coloured liquid that stinks, and it’s basically decomposing waste, and it’s chemically full of lots and lots of contaminants.”
Wright said the 167 olympic pools worth of leachate was a significant amount to be accumulated at the bottom of any tip and that it was “a major issue” for groundwater health.
The landfill is only partially lined and the MRC’s recent request to install a piggyback liner and create a leachate management area in the northern portion of the tip – closest to the nearby residential homes – was rejected by DWER at the beginning of August.
A DWER spokesperson said the high leachate levels was one of the reasons behind the decision.
“Highly elevated leachate levels were a significant consideration during the assessment of a piggyback liner and leachate management area,” they said.
“Following detailed technical assessment, DWER concluded that the proposed works would generate additional leachate and would not adequately address the existing leachate, odour and groundwater issues at the site.”
The regulatory body also acknowledged there are ongoing investigations into groundwater contamination at the site but that there is currently a “low” risk to human health and the broader environment.
Wright said he was “very surprised” the landfill hadn’t been fully lined as to prevent groundwater contamination of the nearby Gnangara aquifer, which provides almost half of all the water used in the Perth metropolitan area each year.
“As soon as I heard about this case study, my mind went straight to: could this be in any way a threat or a risk to Perth’s groundwater? Because the Gnangara sand aquifer is right on the edge of this area,” he said.
“It’s easy for waste from something like this landfill to move through sand down to the aquifer, so as to contaminate the groundwater.”
Wright said groundwater contamination wasn’t the only risk associated with leachate buildup as methane can also be a byproduct of the breakdown of household waste.
“With all this rotting landfill, and particularly the organic wastes that start breaking down, because it’s sealed under metres and metres of landfill, it starts breaking down away from oxygen, and that can create the perfect environment for methane,” he said.
Methane presents a threefold-hazard for Wright: it’s a bad greenhouse gas, it stinks, and it’s explosive.
“The thing with methane is it stinks. There are suburbs growing around here, and I’m actually very surprised there isn’t a larger buffer around this landfill for the suburban development,” he said.
“Methane can also blow up, and one of the concerns in the auditor’s report is that it is an explosive gas, and the gas coming from this rotting waste underground can actually rise through the surface, through the layers of soil and landfill, and if there are buildings nearby, it can sometimes rise into them.
“It can even go through concrete slabs, concrete is a porous material. It can build up in buildings, and yes, it can build up to explosive levels.”
Wright said he would encourage the MRC to embrace the residents and their concerns around the leachate.
“Outrage can ferment with something like this,” he said.
Resident Mary O’Byrne has been championing the odour issue at Tamala Park for years and is now calling on government officials to step in.
“My concern is the groundwater, what’s happening to that, and how it affects residents,” she said.
“I want a government inquiry into how this place is run. I want to know why, for three and a half years, they didn’t evaporate the leachate.”
Wright said he felt like the council was trying to do their best to mitigate the problems that likely began long before most councillors were in their roles.
“I can see that the council is trying their absolute best to take account of all those decisions in the past, and manage it best for locals, but there’s lots of challenges here,” he said.
A spokesperson for the MRC said they were taking the management of the landfill and the protection of the surrounding environment “extremely seriously”.
“Elevated levels of leachate within the landfill is an issue that both MRC and the regulator have been aware of for some time. We share DWER’s concerns on this matter and are committed to finding a viable and lasting solution,” they said.
“MRC presented this information to the regulator voluntarily, and we have worked with the Department for several years to monitor and manage the site’s environmental risks and to ensure the landfill can be safely and successfully rehabilitated.”
But they said they couldn’t quantify the amount of leachate contained within the landfill and that it was a focus of their work in the coming months.
“We continue to deploy measures on site to control the amount of leachate generated, to prioritise the capping of open landfill areas, and to optimise odour management.”
Wright warns however that it will take many decades to manage the leachate issues on the site.
“Grandchildren of people living in this area will still have to deal with this,” he said.
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