Landfill Restoration, Closure and Aftercare
Landfill sites are generally restored (finished) to green space, such as agriculture, forestry or (less often) public open space.
The landfill operator is required to continue to monitor and manage the site post-closure until it can be shown to the satisfaction of the regulator that the active management of the site by the operator is no longer required.
Site Capping and Restoration
Landfill sites are usually restored progressively in phases as the waste mass reached final levels.
The final restoration is usually defined in the Planning Permission for the site.
The final engineering structure is an engineered capping layer on top of the final layer of waste.
Sub-soil and then topsoil is placed on to the engineered capping layer, often termed the restoration levels or horizon.
The engineered capping can be constructed in several ways and the design selected is evaluated in the same way as the landfill lining system, taking account of the various engineering constraints and impacts to be avoided at each site. The design also undergoes similar risk assessment to the lining system. The principle objectives of the engineering capping layer and restoration soils are:
- To contain Landfill Gas within the waste
- To repel/shed rainwater and surface water to reduce the production of Leachate
- To provide a barrier between the waste and the roots of vegetation growing in the soils
- To provide an effective growing medium and afteruse for the site
Typical Capping and Restoration Considerations
Commonly, the capping layer will consist of a compacted clay layer of 1 metre thickness, placed on the last levels of the waste (which is often a thicker layer of final cover to provide a uniform level for placement of the material).
This capping layer can be replaced or supplemented by flexible membranes such as LLDPE (Linear Low-Density Polyethylene) or GCL (Geo-synthetic Clay) in varying combinations. Flexible membranes can be welded together (or fused) similar to engineering lining systems or laid over-lapped with no fused joints. Guidance on landfill capping was published by the Engineering Sub-group of the EA/industry Landfill Regulation Group in 2018.
Soil thickness will depend upon the proposed afteruse of the site; uses involving deep-rooted plants will require thicker soils to protect the engineered capping layer from root-penetration.
Gas and leachate extraction and monitoring equipment (such as monitoring well and pipework) commonly penetrates the capping and soil layers in order to afford access for maintenance and monitoring. Sometimes this equipment is progressively buried with suitable access points remaining at the surface; this is done principally for aesthetic reasons to improve the appearance of the final restored surface.
Site Closure and Aftercare
Landfill sites where all tipping has ceased and the all infrastructure for post-closure management has been installed are deemed "closed" following agreement with the regulator.
Assessment of such a state is measured against criteria identified in WMP26A and subsequent EA guidance. It is generally accepted for non-hazardous landfill sites that this is unlikely to be demonstrated for at least 60 years post-closure or possibly longer. This period is known as the aftercare period.
There is published guidance on landfill permit surrender available from the EA and guidance was updated in January 2025 [1]
