Landfill Gas
Summary
Landfill gas is a mixture of gases generated by the decomposition of organic waste in landfills and waste-filled land. It is primarily composed of methane and carbon dioxide, with trace amounts of other gases that may pose health, safety and environmental risks.
Landfill gas is an important consideration for development on or near former landfills, waste disposal sites or areas of uncontrolled fill, as gas migration can affect buildings, infrastructure and site suitability.
Definition
Landfill gas is produced when organic material breaks down under anaerobic conditions within landfill or waste-impacted ground. The gas typically consists of methane and carbon dioxide, along with trace compounds such as hydrogen sulphide and volatile organic compounds.
Landfill gas can migrate through soil and preferential pathways, accumulate in confined spaces and present explosion, asphyxiation or odour risks if not properly assessed and managed.
Why Landfill Gas Matters
From a health and safety perspective, landfill gas presents both explosion and inhalation hazards. Methane is highly flammable, and elevated concentrations can accumulate in subsurface structures, buildings or service trenches.
From a planning and development perspective, landfill gas can constrain land use and building design. Councils and regulators commonly require assessment of landfill gas risk to demonstrate that proposed development is safe and suitable for occupation.
Landfill gas is also linked to broader contaminated land issues. Gas generation and migration may occur alongside contaminated soil, leachate and groundwater impacts, requiring integrated assessment and management.
Common Sources of Landfill Gas
Landfill gas may be present where land has been used for:
Licensed or unlicensed landfill operations
Waste disposal or dumping
Historical tip sites or refuse pits
Areas of uncontrolled fill containing organic waste
Former industrial or municipal waste facilities
Gas risks may persist long after landfilling activities have ceased.
When Landfill Gas Is Typically Assessed
Assessment of landfill gas is commonly required where:
Development is proposed on or near former landfill sites
Buildings are proposed over waste-filled land
Ground disturbance may create new gas migration pathways
Councils require confirmation of site suitability
Environmental due diligence identifies potential landfill risk
Assessment is typically undertaken as part of a broader environmental site assessment or contaminated land investigation.
Legislative and Regulatory Context
Landfill gas is addressed through contaminated land frameworks, planning controls and environmental guidance.
In New South Wales, councils and regulators commonly require landfill gas risk assessments to support development applications on former landfill land. Similar regulatory expectations apply in other Australian jurisdictions.
Regulatory focus is on identifying gas risks and demonstrating that appropriate mitigation measures are in place.
How We Can Help
Confluence Environmental assesses landfill gas risk as part of contaminated land, development and environmental due diligence projects.
Our services typically include:
Desktop review of landfill history and site conditions
Assessment of landfill gas risk and migration pathways
Integration of landfill gas considerations into site investigations
Advice on mitigation and management measures
Reporting to support planning approvals and compliance
We focus on providing clear, defensible advice aligned with regulatory expectations and site-specific risk.
Related Terms and Concepts
Contaminated Land
Environmental Site Assessment
Groundwater Investigation
Soil Vapour Assessment
Environmental Due Diligence
Development Application