Characteristics

Galligu is a waste of the LeBlanc process used to make soda ash from sodium carbonate in the late 19th century and is principally composed of calcium sulphate. It is estimated that 2 tons of galligu are produced for every 1 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 – meaning it loses strength when disturbed, moved or subject 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

The principal hazard posed by galligu is its poor geotechnical properties. However, when wettened, for example by percolating rainwater, under anaerobic (low/ no oxygen) conditions galligu reacts to form hydrogen sulphide – a hazardous gas with the characteristic smell of rotten eggs. Due to its chemistry, galligu would require specific health & safety precautions to be taken when galligu is being disturbed for treatment or removal. Void spaces can form within the material which fill will hazardous gases. Galligu can have very low pH (acidic) that can cause damage to construction materials and personal injury.

Pathway

Exposure to galligu is mainly a concern to workers or anyone trespassing on to a construction site where galligu has been brought to the surface or 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 affecting any buildings or infrastructure overlaying 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. As such 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 ought to 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 is the former Friars Goose Alkali Works and Allhusens Works in each case galligu was disposed of onto surrounding land. During the Felling Riverside reclamation works chemical waste was reshaped into a new landform for sports pitches, protected with a sealed capping layer. Thixatropic 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 and does not occur naturally.

Site investigation

Desk study

Useful information on previous site investigations may be available via the Gateshead Council planning department.

Walk over

Areas suspected of having had galligu waste disposed 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, for example colliery or coal, derived wastes. 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 Investigations

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 the site investigation sampling, analytical strategies and the health and safety plan 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 either has to be removed or improved (e.g. through stabilisation) or loads transferred by piling through the waste into underlying competent ground.

Remediation

TBA

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 & stabilisation (successfully used in Widness for galligu with leachable Arsenic, Lead & Zinc).

Source removal

Thixotropic galligu has been excavated and replaced 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

• Leblanc process: an early industrial process developed to produce soda ash (sodium carbonate). It was used throughout the 19th century, named after its inventor, Nicolas Leblanc
• Soda ash (aka soda): sodium carbonate; galligu: thixotropic alkali waste arising from the Leblanc process (aka sulphur waste, alkali waste, tank waste, vat waste). Thixotropic: a material that exhibit lower viscosity (informally, ‘thickness’) when a change of pressure is applied through, for example, movement or disturbance.

Document contact

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