Radioactive waste from the nuclear industry and hazardous products from chemical industries need to be effectively isolated from the biosphere for a very long time. Highly radioactive waste gives off heat and requires disposal at depth in special repositories while low-level radioactive waste, pesticides and mercury and arsenic, can be stored in deep mines. The multiple barrier principle implies that the rock and engineered barriers combine to provide isolation but assessment of the constitution and performance of crystalline rock reduces its role to provide “mechanical support” to waste containers rather than true isolation of them. Smectitic clay is required for achieving this but its isolating capacity is limited over time, and long-lasting waste containers are needed as well. The waste isolation effect of clay and containers can allow for constructing repositories in rock of rather poor quality, represented by abandoned mines, and waste containers of 100 % copper further reduce the need for very well planned and constructed repositories.