The official definition of hazardous waste is waste in liquid, solid, contained gas, or sludge form with properties that are potentially harmful to humans or the environment. Tons of hazardous waste are put in landfill sites each year, which can be in or on the ground in landfill, injection well or other unit.
Putting hazardous waste into landfill removes it from the environments people usually inhabit, reducing the risk that people will come into contact with the material. Further, in many cases, putting waste into landfill is cheaper than incineration or materials recovery, at least initially. Removing hazardous waste to regulated landfill sites means, in theory, that it will be managed and monitored appropriately and that any potential problems will be dealt with before they become dangerous to the public.
Placing hazardous waste in landfill sites, rather than reprocessing it, means that the danger is still present and people might still come into contact with the material. Natural events, such as flooding, earthquakes or tsunamis, can very quickly nullify all the care that has been taken of hazardous waste and distribute the hazardous material randomly into the environment. Mismanagement of hazardous waste, of which there are many examples throughout the world, can be extremely dangerous too.
For some materials, like PVC, landfill is actually safer than incineration, according to the OECD. Further, landfill has led directly to the development of landfill tax. According to the OECD, the tax has influenced businesses to recycle, reuse or minimise their waste.
Landfill sites give people an easy way to dispose of their waste and hazardous waste. This may encourage inconsiderate use of hazardous and potentially hazardous materials. Every time people dispose of pesticides, paints, solvents, oils, antifreeze and other chemical products, even when they dispose of them properly, it contributes to the world's hazardous waste.