Landfill in LCA: Why Modelling Choices Matter | Lifecycles
Accounting for landfill in LCA: Why the modelling choices matter
Landfill is the most common end-of-life pathway in Australia. Yet the way we model it in LCA is riddled with inconsistencies, contested assumptions, and decisions that can swing results dramatically.
Tim Grant's recent ALCAS webinar tackled this head-on — walking through the key choices practitioners face when modelling landfill and why, decades into LCA practice, these questions still aren't settled. Here's a summary of the main issues.
Landfill isn't going away
Australian disposal rates have barely shifted in recent reporting periods. Paper entering landfill has dropped significantly since the early 2000s, and organic waste is starting to trend down with the rollout of food and garden organics collection. But overall, the waste bin remains heavier than the recycling bin for most Australians. Waste accounts for roughly 5% of national greenhouse gas emissions — not the biggest contributor, but far from irrelevant.
Methane recovery from Australian landfills sits at about 43% of generated methane, and that figure has plateaued. Current emissions largely reflect waste and engineering decisions made 30 to 50 years ago. The regulatory baseline for carbon offset projects is 30% capture, with a maximum claimable rate of around 70–75%.
The carbon storage question
A significant fraction of biogenic carbon entering landfill stays put. Within a 100-year timeframe, about 90% of carbon in wood products remains stored, and around 73% for some paper products. For wood, this can flip the greenhouse gas profile from net emitter to net sink.
But should we credit this storage? And to whom? In a standard Australian LCA using AusLCI data, the credit flows to the product system — a building gets the benefit of its timber framing being stored in landfill. Australia's national accounts also claim this store.
The EN 15804 standard for EPDs takes the opposite view: all biogenic carbon entering landfill must be treated as fully released through a "virtual emission," even though the carbon is still underground. The rationale is permanence — without a guarantee it stays stored indefinitely, the standard refuses to grant the credit.
The inconsistency: When biogenic material is combusted in waste-to-energy, the CO₂ is counted as carbon-neutral. But landfill storage is penalised with a virtual emission that doesn't reflect reality. Waste-to-energy ends up looking better on paper for biogenic materials because of an accounting rule — not because it delivers a better atmospheric outcome.
Methane capture: past average or future reality?
That national 43% capture rate is a historic figure reflecting the entire stock of Australian landfills — including old, poorly engineered sites with no gas capture. A product manufactured today will likely end up in a landfill licensed decades from now, built to higher standards with 70–90% gas capture. Should we model the average of the past or the best estimate of the future?
There's also the question of who benefits from the energy generated. Under AusLCI, the product system that supplied degradable material gets both the methane burden and the electricity credit. Under EN 15804 rules, the energy credits go to the electricity grid instead — meaning the product cops the emissions but not the offsetting benefit.
Plastics and bioplastics: a different set of problems
Conventional fossil-based plastics barely degrade in landfill, effectively locking fossil carbon underground again. Yet there's no requirement to add a "virtual emission" for this storage — an inconsistency with how biogenic materials are treated.
Bioplastics complicate things further. PLA degrades only about 5% in anaerobic landfill conditions over 100 years. And the common "compostable" bin liner — PBAT blended with thermoplastic starch — is 50% fossil material with similarly low degradation. Australia's most widely used compostable polymer is half fossil, and any biogas it produces in landfill contains a fossil carbon fraction.
What practitioners should take away
These aren't academic distinctions. The choices a practitioner makes on carbon storage, capture rates, degradation fractions and energy credit allocation directly shape whether landfill, recycling or waste-to-energy comes out ahead in a comparative study — and by extension, they influence product design, packaging policy and infrastructure investment.
Two things matter above all else: transparency and sensitivity analysis.
Whatever assumptions you make, state them clearly so results can be interpreted and verified. And test whether alternative assumptions change the direction of your results. In many cases, the full range of defensible choices may point the same way — and that's a far stronger basis for a recommendation than a single scenario that happens to look precise.
Tim Grant presented this topic on behalf of the ALCAS monthly webinar. For the detailed analysis and data behind these issues, watch the full video via the link below.