Wastes that cannot be recycled have to be treated and then deposited in a landfill. In the past, dumping - the most ancient form of disposal - was generally uncontrolled. Today, in Switzerland, landfill sites are classed in one of three categories, according to the types of waste they can accept:

The Technical Ordinance on Waste (TVA) specifies stringent requirements for waste that is to be landfilled, particularly at sites designed for inert materials. Materials that may be disposed of in residual-waste landfills should generally yield a leachate that can be discharged to receiving waters without first being treated. Bioreactor landfills require long-term efforts to monitor and treat gases and contaminated leachate. The processes occurring within the landfill continue for decades and cannot, in the event of an incident, be "switched off" within a matter of hours like the furnace of a municipal waste incinerator. Over a period of decades, despite the use of gas capture systems, substantial amounts of methane and other undesirable gases are released into the atmosphere from bioreactor landfills. There is also a non-negligible risk of defects in sealing systems leading to contamination of groundwater. These crucial factors underlie the prohibition on the direct landfilling of municipal waste, sewage sludge and other types of combustible waste which came into effect on 2000. At the end of 2002, the total capacity available at bioreactor landfill sites was about 19.1 million cubic metres, including 10.8 million for incinerator slag. At landfills for stabilized residues, Switzerland has a reserve capacity of about 2.5 million cubic metres. With annual disposal volumes of just under 500,000 cubic metres of slag and 50,000 cubic metres of residual wastes, this capacity is sufficient for more than 25 years. With regard to reserve capacity at the inert-material landfills operating in this country, the data available are incomplete at present. Even if sufficient capacity is available overall, there is a lack of space for landfilling in geologically unfavourable regions. As a result of the rapid growth in waste streams, cantonal authorities will be forced to continue reviewing their landfill planning in a coordinated fashion. In addition, appropriate funding of landfill maintenance and aftercare will become increasingly important in future.

1. Landfills for inert materials

At landfills for inert materials, only rock-like wastes may be disposed of, from which virtually no pollutants will be leached out by rainwater. These include materials such as construction waste (concrete, bricks, glass, road rubble) and uncontaminated soil that cannot be used elsewhere. At suitable locations, landfills for inert materials do not require any special sealing. They are thus less costly and require less monitoring than other types of landfill. Guidelines issued by FOEN specify the types of waste that may be disposed of at landfills for inert materials.

2. Landfills for stabilised residues

Landfills for stabilised residues are designed for the disposal of materials of known composition, with high concentrations of heavy metals and only a small organic component, and which cannot release either gases or substances readily soluble in water. Typical materials include solidified fly ash and flue gas cleaning residues from municipal waste incinerators, and vitrified treatment residues. These sites are subject to more stringent requirements than landfills for inert materials. Impermeable linings are required for the base and sides of the landfill, and leachate is to be collected and, if necessary, treated.

3. Bioactive landfills

All other types of landfillable waste have to be disposed of at bioactive landfills, in which chemical and biological processes are expected to occur. At these sites, drainage controls are also required. In addition, any gases emitted are to be captured and treated. Given the unpredictable composition of their contents, bioreactor landfills are at greatest risk of requiring expensive remediation at a later date. Certain types of waste (e.g. incinerator slag) are required to be disposed of in separate compartments, isolated from other types of waste. If these wastes were intermixed, heavy metals would be leached out in much greater quantities as a result of the relatively low pH of incinerator slag. Compartments for residual wastes have also been established at numerous bioreactor landfill sites.