Gateshead BGR_Calc ground risk factsheets – Landfill

Characteristics

The critical characteristic of landfills is that their contents are variable in both composition and physical state. Such uncertainty poses health, environmental and financial risks to development. Understanding the history of the landfilling and the way the land surface has changed over time is a helpful starting point in characterising, and if necessary remediating, old landfill sites on or adjacent to new developments.

Hazardous properties

Landfill hazards can be broken down into: contamination, geotechnical, hazardous gas and leachate. Geotechnical properties include poor load bearing and great potential for differential settlement affecting both buildings and subsurface utilities or roads and pavements. Contamination arises from the range of chemicals present in the wide variety of buried waste materials. As waste decomposes, it releases a changing mixture of hazardous gases that can poison, asphyxiate or explode. Landfill gas and leachate can migrate laterally affecting development sites adjacent to, or in the vicinity of, the landfill. Along with gas, waste decomposition results in liquid leachates often of low pH (i.e. acidic) that can pollute groundwater or connected surface water bodies.

Pathway

Poor load bearing properties can damage overlying buildings and structures. Direct contact of people with soil contamination and leachate or inhalation of hazardous gases. Collection of explosive gas in confined space and explosion following an initiation event.

Occurrence

In Gateshead, landfilling of former quarries was predominately with colliery ash and general made ground. However, major landfilling of former quarries and valleys with domestic waste has occurred in the Windy Nook area, Beggars Wood area and in the Blaydon area. During extensive demolition of high-rise tower blocks and Victorian housing in the 1980s, there was a trend to use demolition waste as a fill material for the core of landscaping perimeter mounds of development sites or public open space areas such as the 1990 National Garden Festival site (Dunston / Teams). In the Felling Riverside and Bill Quay areas chemical waste has been spread over much of this area and used to backfill former clay quarries (e.g. Gateshead Stadium pitches site). The chemical industries also generated substantial amounts of waste material, some of which was disposed of locally. Some of the Landfills in Gateshead are unlined and uncapped, other are both lined and capped and include leachate and gas management systems.

Natural occurrences

Landfilled wastes are not natural deposits but can often be found in natural or man-made depressions or low-lying land.

Site investigation

Desk study, walkover and intrusive investigation

Normal review of historical mapping and regulatory records will identify land used for landfilling or land that has been infilled or raised, potentially by waste and the date it was disposed. This should lead to an understanding of the contaminants that might be presented and/ or the likely geotechnical properties. It should also review any pollution control measures expected to be present. The extent of landfilled areas is not always accurately known even for sites that were regulated. Inferred extents from changes in topographic maps as well as satellite imagery can help delineate the extent of buried wastes. Major industrial facilities should be expected to have their own waste disposal locations that might not be recorded elsewhere. These may have been built over as works expanded. Such industrial wastes will reflect the facilities industrial processes and will be relatively homogenous compared with municipal solid waste landfills. The Environment Agency Historic Landfill Sites data set defines the location of, and provides specific attributes for, known historic (closed) landfill sites, i.e. sites where there is no environmental permit. https://data.gov.uk/dataset/17edf94f-6de3-4034-b66b-004ebd0dd010/historic-landfill-sites Landfills can have uneven surfaces and host physical hazards if the waste is not adequately covered. Areas of unexpectedly poor vegetation may indicate hazardous materials or the escape of hazardous gases including methane. Drains and water courses may contain aggressive chemicals and should be avoided both for their physical as well as chemical or biological hazards.

Intrusive Site Investigations

Site investigations need to establish the extent and depth of waste, its composition, gas generation potential and geotechnical properties. Drilling through the base of a landfill should only be carried out if any leachate at the base of the waste can be contained and not allowed to drain deeper down the borehole. Hazardous ground gases are generated by decomposing waste and can migrate laterally along geological horizons, backfilled utility trenches or pipework if there are low permeability capping layers above the waste.

Foundations

Landfills generally have poor geotechnical properties and usually require special foundations to both reach load bearing ground and to withstand the often aggressive chemistry in landfills. Landfills generating hazardous gases that need active gas control.

Remediation

Pathway interruption

Development, including occupiers of buildings, are often protected by gas or vapour proof membranes intended to keep hazardous gas out of the building. Such membranes need to be made of material appropriate to the gas or vapour composition and installed properly.

Source removal

Excavation, material recovery and residue disposal elsewhere is an increasingly adopted approach to rendering landfill sites suitable for residential development.

Waste disposal

Landfills contain historically disposed waste materials and any material generated during drilling or excavation would need to be disposed of in accordance with current legal requirements.

Regulatory aspects

The extent to which a historic landfill will have been regulated depends on both when it was receiving waste and the composition of that waste.

Document contact

Dr Darren Beriro (darrenb@bgs.ac.uk)