The landfill regulations require landfills to be classified as taking waste under one of three headings: hazardous, non-hazardous or inert. Non-hazardous landfills can, however, accept stable, non-reactive hazardous waste provided it is not deposited in cells for the disposal of biodegradable waste.
From 16 July, when the full "waste acceptance criteria" for landfills come into effect, gypsum and other high sulphate-bearing materials will only be acceptable in such separate cells. Asbestos or construction material containing asbestos must be deposited in separate cells or in a dedicated asbestos landfill.
Suitable wastes, says the Agency, are likely to include monolithic solidified wastes or granular solid wastes produced by treatment plants, such as filter cakes and treated fly ash.
There must be no physical contact between the stable, non-reactive hazardous waste and the biodegradable wastes, and the leachate and landfill gas systems for each type of waste should also be separate.
Cells for the two types of waste can be separated either by dedicated structures or the managed placement of non-hazardous waste, such as contaminated soil, which does not contain any biodegradable waste.
In the latter case, a "significant width" of non-biodegradable, non-hazardous waste is likely to be needed, while there should be sufficient thickness of such waste beneath the hazardous waste to ensure that it is "well above" the maximum level of leachate produced by the biodegradable waste.
The construction of separate cells by lining over pre-existing waste is unlikely to be acceptable.
In addition to the construction of asbestos cells adjacent to those for non-hazardous waste, asbestos cells can also be constructed below the non-hazardous wastes provided a cell separation liner is used and the upper surface of the asbestos wastes is covered with a stable two-metre layer of suitable material.
The construction of asbestos cells using the managed placement of non-biodegradable, non-hazardous waste is not included as an option.
The rules for such cells are similar to those for stable, non-reactive wastes. Engineered separation is "likely to be the easiest option in practice", but managed cell separation by segregation of wastes is permitted provided the properties of the waste acting as the barrier prevent contact between leachate and gas from biodegradable waste and the wastes with high sulphate content.