A deep geological repository is a way of storing hazardous or radioactive waste within a stable geologic environment (typically 200–1000 m deep). It entails a combination of waste form, waste package, engineered seals and geology that is suited to provide a high level of long-term isolation and containment without future maintenance. This will prevent any radioactive dangers. A number of mercury, cyanide and arsenic waste repositories are operating worldwide including Canada (Giant Mine) and Germany (potash mines in Herfa-Neurode and Zielitz) and a number of radioactive waste storages are under construction with the Onkalo in Finland being the most advanced. Principles and background Highly toxic waste that cannot be further recycled must be stored in isolation to avoid contamination of air, ground and underground water. Deep geological repository is a type of long-term storage that isolates waste in geological structures that are expected to be stable for millions of years, with a number of natural and engineered barriers. Natural barriers include a water-impermeable (e.g. clay) and gas-impermeable (e.g. salt) layers of rock above and surrounding the underground storage. Engineered barriers include bentonite clay and cement. The International Panel on Fissile Materials has said: It is widely accepted that spent nuclear fuel and high-level reprocessing and plutonium wastes require well-designed storage for periods ranging from tens of thousands to a million years, to minimize releases of the contained radioactivity into the environment. Safeguards are also required to ensure that neither plutonium nor highly enriched uranium is diverted to weapon use. There is general agreement that placing spent nuclear fuel in repositories hundreds of meters below the surface would be safer than indefinite storage of spent fuel on the surface. Common elements of repositories include the radioactive waste, the containers enclosing the waste, other engineered barriers or seals around the containers, the tunnels housing the containers, and the geologic makeup of the surrounding area. A storage space hundreds of metres below the ground needs to withstand the effects of one or more future glaciations with thick ice sheets resting on top of the rock. The presence of ice sheets affects the hydrostatic pressure at repository depth, groundwater flow and chemistry, and the potential for earthquakes. This is being taken into consideration by organizations preparing for long-term waste repositories in Sweden, Finland, Canada and some other countries that also have to assess the effects of future glaciations. Despite a long-standing agreement among many