Landfill remediation: Enviropacific team reduces the risks

Numerous landfills across Australia have been repurposed into sports fields and public areas. Others have been capped and left idle once they’ve reached capacity.

But what's buried doesn't always stay buried. Solid waste, methane gas and leachate can escape from landfills decades after they’re no longer in use, creating environmental and health hazards.

That's where environmental services specialist Enviropacific steps in.

The company's remediation division has experience in landfill remediation projects, from retrofitting gas and leachate management at existing sites to full remediation involving recovery, processing and removal of the waste.

Fred Lunsmann, Enviropacific General Manager – Remediation, says there's been a rise in the requirement for mitigation works in the past five years, driven by increased regulation and encroaching development.

"Historically, the Environment Protection Authority might have overlooked legacy landfills but now it's more active about managing these environmental impacts," he says.

"If development is encroaching, the risk profile to people living or working around it increases."

Methane gas is created as landfilled waste decomposes. Fred says that most old landfills don't have the infrastructure to manage the collection and safe venting of the gas, which can pose a health hazard and explosion risk. Landfill leachate, a wastewater formed by rainwater and moisture flowing through the buried waste, is particularly prevalent in historical landfills with inadequate infrastructure.

Martin Kelly, Enviropacific Pre-contracts Manager, says off-site migration of leachate or methane gas can still be detected up to 20 years after a landfill has been closed.

"The waste is still there," he says.

Landfill remediation is driven by the site itself, taking into account its current use and what's been buried there previously.

Historical licences, weigh bridge records and a drilling investigation into the landfill mass can all help determine the remedial strategy.

The impact on surrounding communities, such as dust and odours, is also a key element in planning.

"The challenge is the unknown," Martin says. "With remediation it's what's under the ground that is generally the problem. You expect everything because you really don't know what has been tipped in there."

Enviropacific recently constructed a methane interception trench for a site at Silverwater, to stop gas from a legacy landfill migrating to nearby industrial properties.

Martin says the 90-metre trench was filled with gravel and capped with a slotted pipe which forced the gas up to a carbon canister.

He says monitoring since the completion of the project shows that methane levels have dropped.

A similar ideology is being used to redirect methane coming from a sporting oval built over a former landfill at Hornsby, in New South Wales. A series of vertical bores will be installed to allow the gas to vent into the air before it reaches neighbouring residential properties.

Other strategies can involve erecting a cut-off wall around a landfill, or landfill cell, to stop gas or leachate migrating so it can possibly be extracted. In some instances, old landfill caps, traditionally a geo synthetic clay liner placed on top of a landfill to prevent water ingress, deteriorate over time and need replacing.

Some landfill remediation projects need more than a mitigation approach.

In 2018, Enviropacific remediated the former Narellan landfill back to a residential standard. The project earned Enviropacific the 2018 Sustainable Project Recognition Award from the Australian Land and Groundwater Association (ALGA).

The site, at Elyard Street, Narellan now sits in a prime development location and has the potential to produce economic and social benefits for the surrounding community.

Fred says the 16-month project was complex and required several remediation strategies. Being a former uncontrolled landfill, the range of contaminants was wide-ranging and included heavy metals, volatiles, degrading putrescible waste, asbestos, ground gas, and contaminated groundwater.

The project was partly to remove waste but also to recover and reuse as much recyclable material as possible. Materials for potential reuse were progressively excavated and processed onsite, with unsuitable contaminated materials disposed.

"There was 84,000 cubic metres of waste in the cell," Fred says. "We recovered 17,000 cubic metres of soil and crushed concrete that was able to be reused rather than taken offsite.

"There were a lot of trials and onsite testing to assess potential settlement and re-gassing from the processed material.

"We really had to align the environmental requirements with the geotechnical requirements."

The project resulted in the extraction and treatment of 11 million litres of landfill leachate, the reuse of two million litres of surface water, excavation of 84,000m3 of uncontrolled landfill materials, crushing and recovery of 5000 cubic metres of concrete and brick, recycling more than 150 tonnes of steel and other recyclables and recycling and shredding more than 4000 waste tyres.

For more information, visit: www.enviropacific.com.au

METBERG ENVIRO METBERG ENVIRO 3000

$160,000

Angle Park, SA

2020 SCREENMASTERS SMA804S SCALPING SCREEN

$198,000

Wetherill Park, NSW

2014 KEESTRACK S175

$250,000

Hillwood, TAS

2023 TRICON ENVIRONMENTAL PHOENIX TRACK MOUNTED PUGMILL

$399,000

Wyong, NSW

2013 KIRPY KIRBY RICK CRUSHER

$80,000

Port Pirie South, SA

2018 TESAB TS1550

$300,000

Burleigh Heads, QLD

SYMONS 3FT S/H CONE CRUSHER

$65,000

Wingfield, SA

2006 KOMPTECH MAXX TROMMEL

$217,800

Peak Crossing, QLD

IMS MS842W

$125,000

Burleigh Heads, QLD

LIPPMANN LS 520 TRIPLE DECK RECLAIMER / SCALPING SCREEN

$492,500

Wyong, NSW

2018 PORTAFILL 9000JC

$324,500

Wodonga, VIC

MAXIMUS SMA TFC80

$330,000

Wetherill Park, NSW