Characteristics
Galligu is a waste product of the LeBlanc process, which was used to make soda ash from sodium carbonate in the late 19th century and is principally composed of calcium sulphate. It is estimated that two tons of galligu are produced for every one ton of soda ash.
Galligu contains high levels of arsenic and other heavy metals. Galligu was either disposed of in spoil heaps or used to infill valleys or build embankments.
Its physical properties vary depending on its state of oxidation and water content. When dry, it has a silty sand texture, but when wet, the waste rapidly softens and becomes thixotropic — it loses strength when disturbed, moved or subjected to a change of pressure.
As well as the pollution risks posed, galligu's uncontrolled disposal in areas surrounding the factories has resulted in significant ground stability problems.
Hazardous properties
Due to its chemistry, galligu would require specific health and safety precautions to be taken when it is being disturbed for treatment or removal.
The principal hazard posed by galligu is its poor geotechnical properties. However, when wettened, for example by percolating rain water, under anaerobic (low/no oxygen) conditions, galligu reacts to form hydrogen sulphide. This is a hazardous gas with a characteristic smell of rotten eggs.
Void spaces can form within the material, which fill with hazardous gases.
Galligu can have very low pH (acid) that can cause damage to construction materials and personal injury.
Pathway
Exposure to galligu is mainly a concern for workers or anyone trespassing on a construction site where galligu has been brought to the surface or had its cover removed.
Where hydrogen sulphide has been generated, inhalation of the gas is possible whilst the galligu remains buried.
If galligu is left in the ground during site redevelopment, it can become unstable and cause ground subsidence that will affect any buildings or infrastructure overlying the material.
Occurrence
The industry developed where the essential raw materials of rock salt, coal and limestone were in plentiful supply, including the riverside area between Saltmeadows and the Bill Quay area on Tyneside. Galligu was disposed of in mounds or spread over much of the land in the Saltmeadows, Felling Riverside and Bill Quay areas. The waste was also commonly used as fill for railway embankments in that area.
Any areas of fill and made ground in that area ought to be considered as possibly containing galligu and the site investigation sampling and analytical strategies, as well as the health and safety plan, should be designed with this in mind. However, some of the galligu was processed to recover sulphides and sulphates from the waste.
The main sources of galligu in Gateshead are the former Friars Goose Alkali Works and Allhusen’s Works: in each case, galligu was disposed of onto surrounding land. During the Felling Riverside reclamation works, chemical waste was re-shaped into a new landform for sports pitches, protected by a sealed capping layer.
Thixotropic chemical waste material was removed from the base of the former clay pit and sealed into a purpose-built encapsulation waste facility adjacent to the site.
Natural occurrences
Galligu is an industrial waste material and does not occur naturally.
Site investigation
Desk study
Useful information on previous site investigations may be available via the Gateshead Council planning department.
Walkover
Areas suspected of having had galligu waste disposed on them may pose a physical hazard.
The blue/green and grey forms of galligu should be readily identifiable, however, black ashy galligu may be more difficult to differentiate from other derived wastes, for example those from colliery or coal workings.
Attention should be paid to the potential presence of void spaces in the galligu, which can be filled with hazardous gases as well as pose a physical hazard.
The high pH of galligu can lead to personal injury during walkovers.
Intrusive site investigation
Areas of fill and made ground in areas where galligu could have been disposed of ought to be considered as possibly containing galligu. In these areas, any site investigation sampling, analytical strategies and health and safety plans should be designed with this in mind:
- ground-gas monitoring for hydrogen sulphide
- soil testing for pH and elemental sulphur, sulphate and sulphide, and leachable sulphate
- ground may be thixotropic and drilling vibrations could cause instability
Foundations
Galligu is not a load-bearing material. It has to be removed, improved (e.g. through stabilisation) or loads need to be transferred by piling through the waste into underlying, competent ground.
Remediation
Pathway interruption
A clay cut-off wall and a 1 m clay cap were used during the Felling Riverside Phase 1 reclamation to isolate galligu as part of a landscaping operation.
In situ solidification and stabilisation were successfully used in Widnes, Cheshire, for galligu with leachable arsenic, lead and zinc.
Source removal
Thixotropic galligu was excavated and re-placed into a purpose-built encapsulation during the Felling Riverside Phase 2 reclamation.
Waste disposal
Galligu's chemical and physical (thixotropic) properties will need to be accounted for when classifying it and arranging for its disposal and, if necessary, transport.
Regulatory aspects
No galligu-specific regulations exist.
Glossary
Galligu: thixotropic alkali waste arising from the Leblanc process (also known as sulphur waste, alkali waste, tank waste or vat waste).
Leblanc process: an early industrial process developed to produce soda ash (sodium carbonate). It was used throughout the 19th century and is named after its inventor, Nicolas Leblanc.
Soda ash: ('soda') sodium carbonate.
Thixotropic: a material that exhibits lower viscosity (informally, 'thickness') when a change of pressure is applied through, for example, movement or disturbance.
References
Read, P. 2013. Galligu: an environmental legacy of the Leblanc alkali industry, 1814–1920. Royal Society of Chemistry Environmental Chemistry Group Bulletin, February 2013.
Royal Commission on Noxious Vapours. 1878. Report of the Royal Commission on Noxious Vapours. (London, UK: Her Majesty's Stationery Office.)
Document contact
Dr Darren Beriro: darrenb@bgs.ac.uk