A closed landfill has ceased accepting waste and entered a formal post-closure care phase. This initiates a long-term management period where future development is possible under strict regulatory oversight. The closure process isolates the waste mass from the environment, making the land available for beneficial reuses that do not compromise the protective systems. Repurposing requires detailed engineering to ensure public safety and environmental protection.
Mandatory Steps Before Repurposing
The foundational requirement for any landfill reuse project is the installation and certification of a final cover system, or cap. This engineered, multi-layered barrier minimizes the infiltration of surface water into the buried waste mass. A typical cap includes an infiltration layer, often consisting of a geomembrane or compacted clay, covered by an erosion layer of topsoil capable of supporting vegetation.
The infiltration layer must be constructed with a permeability no greater than 1.0 x 10^-5 centimeters per second. This low-permeability barrier prevents the “bathtub effect,” where water accumulation inside the waste creates excessive pressure on the bottom liner. The cap is then covered with at least 6 inches of earthen material to support plant growth and prevent erosion.
Management of decomposing waste byproducts must continue indefinitely after closure. Leachate, the liquid formed as water percolates through the waste, is collected and treated before disposal. Landfill gas (LFG), which is 40 to 60 percent methane, is collected to prevent off-site migration and explosion hazards. Regulatory requirements mandate that methane concentrations must not exceed 25 percent of the lower explosive limit (LEL) in facility structures. This monitoring and maintenance phase typically lasts for a minimum of 30 years, or until the site demonstrates stability regarding settlement, gas production, or leachate generation.
Transforming Landfills into Energy Hubs
The large, open expanses of former landfills are well-suited for generating renewable power, offering a productive use for otherwise undevelopable land. Solar photovoltaic (PV) arrays are a common choice because they utilize the surface area without requiring heavy structures or deep foundations that could breach the cap. Installation uses a ballasted foundation, relying on heavy concrete blocks or trays to hold the panels in place against wind uplift.
This non-penetrating approach is necessary because driving piles into the ground would puncture the final cover’s geomembrane or clay layer. Differential settlement, caused by the uneven decay of waste material, is managed using flexible mounting systems or fixed-tilt arrays. Some modern projects use low-profile, rackless solar systems that adhere directly to an engineered geosynthetic turf cover, allowing installation on steeper landfill slopes.
The contained waste also serves as an energy resource through landfill gas (LFG) collection systems. Methane, the primary component of LFG, is a potent greenhouse gas, making its capture environmentally beneficial. The collected gas is processed and used in several ways, including combustion in engines or turbines to generate electricity. LFG can also be upgraded into Renewable Natural Gas (RNG) by removing contaminants, making the gas pipeline-quality for injection into the natural gas grid.
Creating Public Recreational Areas
Converting a closed landfill into a public recreational space requires designing facilities compatible with the site’s structural limitations. The primary engineering challenge is differential settlement, where the uneven compression of the waste mass could cause cracks in the protective cap. Consequently, reuse is restricted to lightweight, flexible amenities such as municipal parks, hiking and biking trails, and golf courses.
Any necessary structures, such as restrooms or maintenance sheds, are preferably located outside the waste boundary or built using specialized foundations that accommodate movement. Deep foundations, like piles, are generally avoided over the waste to maintain the cap’s integrity. For amenities like athletic fields, the design must incorporate the landfill’s existing infrastructure, such as rerouting above-ground gas vents or monitoring wells to preserve a continuous play area.
Golf courses and driving ranges are popular options because they require minimal permanent structures and their expansive, contoured landscapes align well with the final grading. When paving for parking lots or trails is necessary, a stable, well-compacted subbase is used to minimize the effects of uneven settling. The vegetative cover is rigorously maintained, often using shallow-rooted grasses to avoid root penetration that could damage the underlying barrier layers.
Ecological Restoration and Habitat Creation
Ecological restoration dedicates the closed landfill surface to functional habitat creation rather than human recreation. This approach often involves re-establishing native ecosystems, such as grasslands or meadows, which provide significant conservation value. These expansive, open habitats can become islands of biodiversity for species like grassland birds and butterflies, especially in regions dominated by agriculture or urban development.
The revegetation strategy selects native, shallow-rooted plants to prevent their roots from compromising the final cap’s infiltration layer. Ecological restoration also leverages the site’s topography for improved stormwater management. Engineered features like constructed wetlands or vegetated swales can be integrated around the perimeter to enhance infiltration and naturally treat runoff before it leaves the site.
Constructed wetlands are valuable for mitigating stormwater runoff, but they are typically located away from the immediate waste mass to avoid placing a permanent water load over the capped area. The primary goal of these projects is self-sustaining ecological function, meaning human access is often restricted to ensure the long-term success and stability of the restored communities. This land use provides a permanent environmental benefit by turning a former liability into a functioning natural asset.