Controlled landfill

A controlled landfill is a waste-disposal facility that meets technical, environmental and safety criteria designed to prevent the deposited waste from polluting the air, water or soil.

Its main features are:

• Lining systems on the base and sides, usually combining compacted clay and high-density polyethylene (HDPE) geomembranes.
• A leachate drainage network that collects the liquids produced by waste decomposition and rainwater infiltration.
• Landfill-gas capture and use, mainly methane and CO2, to generate electricity or heat.
• Periodic covering of waste with layers of soil or other materials to limit odours, pests and fire risk.
• A closure and aftercare plan, ensuring environmental monitoring for at least 30 years after closure.

Types of controlled landfill

The Landfill Directive 1999/31/EC (amended by Directive (EU) 2018/850) and Spain's Law 7/2022 on waste and contaminated soil classify landfills into three categories:

1. Hazardous-waste landfills: accept waste with hazardous properties, under strict safety measures. Example: industrial sludge with stabilised heavy metals.
2. Non-hazardous-waste landfills: for mixed municipal waste and non-hazardous construction and demolition fractions. These are the most common in Spain.
3. Inert-waste landfills: only accept waste that does not undergo significant physical, chemical or biological change. Example: clean rubble, soil and stones without contaminants.

How a controlled landfill works

1. Reception and inbound control: documentary checks (treatment contracts, European Waste Codes) and visual inspection to detect non-authorised waste.
2. Tipping and compaction: waste is deposited in cells and compacted with heavy machinery.
3. Intermediate cover: covered with soil or other materials to limit odours, insects and excessive leaching.
4. Leachate management: collected through pipes and pumped to physico-chemical or biological treatment.
5. Gas management: extraction wells and chimneys; in many cases the biogas is used for energy in cogeneration engines.
6. Closure and aftercare: top sealing with impermeable layers and monitoring of groundwater, gas emissions and structural stability.

Applicable rules

The regulatory framework for landfills in Spain and Europe is broad and strict:

• Landfill Directive 1999/31/EC, amended by Directive (EU) 2018/850 (which sets the target of landfilling no more than 10% of municipal waste by 2035).
• Council Decision 2003/33/EC: criteria for accepting waste at landfills.
• Law 7/2022 on waste and contaminated soil for a circular economy.
• Royal Decree 646/2020 on the disposal of waste in landfills.

Key obligations include:

• Progressively reducing the amount of biodegradable waste sent to landfill.
• Banning the disposal of liquid, flammable, explosive or infectious waste, and whole tyres.
• Requiring environmental impact studies and aftercare monitoring plans.

Environmental risks of landfills

Despite control measures, landfills carry long-term risks:

• Groundwater contamination from poorly managed leachate.
• Methane (CH4) emissions: a gas with a global warming potential around 28 times that of CO2 over 100 years (IPCC AR6).
• Odours and nuisance to nearby communities.
• Proliferation of opportunistic fauna, such as birds and rodents.
• Landscape impact and loss of available land.

Advantages and limitations of controlled landfills

Advantages

• A necessary solution for waste that cannot be recycled or recovered.
• Safety technologies that minimise risks.
• The energy use of landfill gas.

Limitations

• They require large areas of land.
• They create long-term environmental liabilities.
• Their aftercare entails high costs for public authorities.
• They contribute to greenhouse gas emissions.

Alternatives to controlled landfill

To meet European circular-economy targets, landfilling must be progressively reduced through:

• Prevention at source: designing more durable, easier-to-recycle products.
• Reuse and repair: extending the useful life of materials and objects.
• Material recycling: recovery of paper, plastics, metals and glass.
• Energy recovery: harnessing non-recyclable waste as energy.
• Biological treatment of organics: composting and anaerobic digestion.

The controlled landfill remains essential infrastructure in waste management in Spain today. It is a substantial improvement on the uncontrolled dumping of the past, but it is still a last-resort option in the waste hierarchy. The transition to a circular economy requires landfills to be kept to a minimum, prioritising prevention, recycling and recovery. While they exist, they must be managed with the highest technical and environmental guarantees, using landfill gas as an energy resource and ensuring aftercare control for decades.

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