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The Modern Landfill Design Concepts in the UK and Europe which Landfill CQA Engineers Must Implement

There is very little information available about the motivations and origins of the design principles behind the work of a landfill CQA engineer, so we decided to write this (based on a 1994 paper by Harris, Knox and Walker).

CQA principles must logically be applied to all landfills where the wastes accepted potentially pose a risk of water pollution, mainly those accepting household, commercial and industrial wastes. These wastes account for a relatively small proportion of total waste arisings (approximately 20% of the UK’s total of 516 Mt (3), the rest being demolition waste, mining and smelting wastes, fly ash from power stations, sewage sludge and agricultural wastes). Nonetheless, this fraction presents the most intractable difficulties of the total.

Whilst the nature of the wastes deposited in landfills may have evolved through man’s history, the operational methods until recently, remained largely unchanged and unsophisticated.

Over the last forty years or so, a much wider understanding of processes involved in waste stabilization has been developed. This has coincided with a worldwide increasing environmental awareness leading to demands for environmental improvements.

These demands are well founded, in fact although clean unpolluted UK water supplies are, as everywhere, vital for the survival of the population some experts have suggested that as much as one third of all UK groundwater supplies are now contaminated to some extent by pollutants. If the rate of damage to our water resources was sustained for another century the situation would have become extremely serious for public health, even without the further pressures on water supply anticipated from climate change.

Legislation in the UK has matched public demands for change, by the implementation of Directives issued by the Council of the European Communities. Most importantly in the 1980s, the introduction of the Groundwater Directive has caused an evolution in the standards of site preparation works and operational practice being demanded for all new landfill projects in order to prevent pollution of the water environment.

This evolution was accelerated by the inception of the National Rivers Authority in 1989 and the introduction of their Groundwater Protection Policy in December 1992.

The changed requirements have led largely to the discontinuation of the “attenuate and disperse” concept of landfill with the emphasis now on “engineered containment and operational safeguards”.

This is generally achieved by the installation of either an engineered clay liner or a composite liner, so called because it combines the use of natural materials (e.g. compacted clay) with polymeric membranes, otherwise known as flexible membrane liners (FMLs). Using these materials, emphasis is placed on preventing the release of leachate into the geologic environment.

In addition, there are concomitant operational requirements considered necessary to limit further the potential for leachate release from the site. There are two broad components.

The first is concerned with the limitation of leachate production.

This can be effected by infilling in a series of cells sized on the basis of water balance calculations to (in theory at least) avoid the generation of leachate during the operational phase by utilising the absorptive capacity of the waste.

Rainwater accumulating in other parts of the site can be kept separate and discharged in an uncontaminated condition.

Leachate production is further reduced by progressive capping and restoration of each cell as it is infilled to final levels and by ensuring that these restoration layers are laid to a high standard to prevent rainfall infiltration.

The second component is designed to ensure that any leachate produced can be removed easily from the site.

The composite lining system for engineered containment is protected by a blanket of free draining material incorporating a perforated drainage pipework system. Not only will this prevent mechanical damage to the liner, it will also facilitate the easy removal of leachate, limiting the potential for building up a head of leachate in contact with the liner.

The ability to remove leachate easily from the site must then be supported by a reliable system for its disposal.

This is usually the discharge to public sewer with varying degrees of pre-treatment though more rigorous on-site treatment with discharge to stream is increasingly being used as technical and management standards continue to improve.

The broad concepts behind this approach have been accepted and practised in the UK since the mid 1980s.

However, operational experience continued to highlight design and installation problems. Subsequently further design and landfill construction (base and capping) guidance and regulations were introduced through enactment of legislation on site licensing, and then permitting (under IPPC Regs – now known as Environmental Permits), driven by the Landfill Directive, and the amended Waste Directive.

The CQC and CQA engineering carried out as part of Landfill CQA is tasked with ensuring that the final link in the chain is achieved by verifying that the complaint design is fully implemented and achieved or exceeded during site construction.

This is a serious responsibility for the landfill CQC and CQA professionals when one considers the extremely high importance highlighted earlier to all future generations that we get this right, and the water environment does not become further damaged by pollution from landfills.

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