Michael Cowan and Sarah Cillian       Introduction       In the past, when industry grew faster than our understanding for safe chemical cleanup, contaminants were addressed generally through containment. Though conventional methods were capable of stopping contaminants from spreading, it was impossible to restore fully the original conditions of contaminated soils and groundwater. In the last few decades, however, our growing concern for these hazards has led to the development of new soil cleanup methods; one of these is bioremediation, where naturally occurring biological processes are used break down contaminants within soil systems. There are two types of bioremediation: in situ (no removal of soil) and non-in situ (removal of contaminated soils to be treated elsewhere). In situ bioremediation will be the main focus of the present discussion.