If necessary, they decontaminate themselves before leaving the area. Once the material has been identified, other personnel arrive to remove it. In the past, hazardous wastes were buried in special landfills. Some industrial and government operations also used fields, pits, ponds, and lagoons as disposal sites. Over the years many of these leaked, contaminating soil and drinking water.
New techniques look very promising.
For example, certain bioengineered organisms can digest specific hazardous chemicals. Some of these organisms have already been used on oil slicks from ocean spills. Science News, pp. Handle with care. Consumer Reports, p. 101.