Landfills serve as designated sites for waste disposal, but their capacity is finite. When a landfill reaches its full capacity, it triggers a series of planned processes and considerations. These steps ensure environmental safety and potential future land use, encompassing complex engineering, environmental oversight, and broader waste management strategies.
Landfill Closure Procedures
A landfill is considered “full” when it reaches its permitted waste volume and design limits. The formal closure process then begins, involving engineering and regulatory steps to safely seal the waste. A key element is installing a final cover system, a multi-layered cap designed to minimize water infiltration and control gas escape. This cap typically includes a compacted clay layer or a geosynthetic clay liner (GCL) for low permeability, a geomembrane (plastic liner) to prevent liquid intrusion, a drainage layer to manage stormwater, and a protective soil layer capable of supporting vegetation.
The surface of the closed landfill is carefully graded and shaped to promote runoff of rainwater and prevent ponding, which could otherwise compromise the integrity of the cover system. This ensures that water flows away from the waste, reducing the potential for leachate generation. Legally, landfill owners and operators must prepare a written closure plan detailing the design and installation methods for the final cover, an estimate of the area requiring coverage, and a schedule for completion. Upon completion, an independent registered professional engineer or state director must certify that the closure aligns with the approved plan, and a notation indicating the land’s past use and restricted future activities is typically added to the property deed.
Environmental Oversight Post-Closure
Following the initial closure, environmental management and monitoring continue for decades to ensure the landfill remains stable and does not pose environmental risks. This long-term oversight focuses on managing liquids and gases generated by the decomposing waste. Leachate, a liquid formed as water filters through the waste, is collected, treated, and safely disposed of to prevent contamination of groundwater and surface water. Leachate collection systems are continuously maintained, and the collected liquid undergoes treatment before discharge.
Landfills also generate gases, primarily methane and carbon dioxide, from the anaerobic decomposition of organic materials. Methane is a potent greenhouse gas, and its collection is crucial for environmental protection. Gas collection systems, consisting of wells and piping, extract these gases, which can then be flared (burned off) or, increasingly, utilized to generate energy. Continuous monitoring of groundwater, surface water, and air quality around the site detects potential contamination or gas migration, with monitoring typically lasting for at least 30 years or until the site stabilizes.
Strategies for Waste Diversion
Beyond managing closed landfills, broader strategies aim to reduce the amount of waste sent to these sites, extending the lifespan of existing landfills and reducing the need for new ones. The waste hierarchy prioritizes waste management strategies from most to least environmentally favorable: reduce, reuse, and recycle. At the top of this hierarchy is waste reduction, or source reduction, which involves minimizing waste generation at its origin. This can include purchasing products with less packaging or avoiding single-use items.
Following reduction, other strategies include:
- Reuse: Giving products a second life, either in their original form or after modification, keeps materials in circulation and reduces demand for new resources.
- Recycling: Reprocessing waste materials into new products, such as plastic bottles into new containers or paper into new paper products.
- Composting: A diversion strategy for organic materials like food scraps and yard trimmings, which decompose into nutrient-rich soil amendments.
- Waste-to-energy (WTE) technologies: Converting non-recyclable waste into electricity or heat, significantly reducing the volume of waste sent to landfills.
Reclaiming Closed Landfill Sites
Once a landfill has been properly closed and undergone a period of post-closure monitoring, the land can often be repurposed for other uses. While direct construction of heavy buildings can be challenging due to potential settlement and gas management issues, many closed landfills are transformed into beneficial public spaces. Common examples of repurposing include creating parks, golf courses, and recreational areas, such as Mount Trashmore Park in Virginia. These sites can offer hiking and biking trails, scenic overlooks, and even wildlife habitats.
Beyond recreational uses, some closed landfill sites are being repurposed for renewable energy generation, such as solar farms. Developing these sites requires careful consideration of the long-term stability of the land, including potential settlement of the underlying waste and the ongoing management of landfill gas. Ensuring the integrity of the final cover system and managing any residual gas emissions are important factors in the transformation of these former waste disposal areas.