Geomelting is the process by which dangerous, contaminated material (such as radioactive waste and heavy metals) is mixed with clean soil and melted down to create an extremely hard glass product which immobilizes nearly all of the contaminants in the initial mixture. Any gaseous contaminants released during the melting process are treated separately. Developed in 1980 by the US Department of Energy's Pacific Northwest National Lab. (PNNL), Geomelting occurs in one of two ways: in situ (on-site) treatment of hazardous materials and off-site treatment of such materials (ie, waste is transported to treatment facility). Geomelting is based on the principle of vitrification, the process by which a glass is formed. To effectively vitrify any mixture of materials, substances that contribute to glass formation (called glass formers) must be present. These glass formers usually contain silicon and oxygen and are present in most soils. Much of the efficiency of this process has to do with how much waste material can be mixed with glass formers. Industrial-scale melts have shown that a stable glass compound is formed even when the original melt mixture is up to 33-40% waste material by weight, depending on the type of waste.