The guidance note provides interim guidance for Northern Ireland's Environment and Heritage Service staff and landfill operators on the capping of landfill sites and the procedures that can be applied to both existing and new landfill sites.
The document provides an overview of the main considerations when establishing capping standards.
The capping of landfill sites is clearly of great importance from a human and environmental protection viewpoint. It effectively isolates the waste mass from the surroundings, helps control the amount of water entering the site and will provide control for the landfill gases generated within.
Regardless of the regulatory regime the design of a landfill cap needs to be risk based and hence developed under a site specific risk assessment, e.g waste accepted, overall design, context and the site history.
The guidance splits landfill sites into two broad categories as non-Landfill Directive compliant sites and Directive compliant sites with sub-divisions provided for each.
The Landfill Directive itself provides 'guideline' standards for capping which are reproduced in the guidance, dependent on whether sites are hazardous or non-hazardous.
The guidance indicates that as a minimum, the capping system should contain a low permeability/sealing layer, a surface drainage system and cover soils. All hazardous and non-hazardous landfills will require a cap.
However the appropriate engineering requirements should be determined based on a site
specific assessment of the nature of the hazard that the landfill poses and the risks that it presents to the environment in both the short and the long term.
The guidance also deals with inert landfill sites, which may themselves require capping dependent of the risks from some of the materials contained.
From the editor's experience many historic "inert" sites are capable of producing elevated methane levels.
The guidance document covers amongst others:
- Regulatory requirements
- Design of landfill caps
- Restoration of landfills
It also provides a useful glossary of terms, key references and a table showing the specification of the minimum compost quality for general use as an Appendix.
Further information
The guidance document on capping and restoration of landfills can be downloaded from the EHS website.