The parameters which are assessed for acceptability in chemical treatment of soil depends primarily on the aim of the improvement process. For instance, if the objective of improvement is to stabilise and solidify contaminated soil and prevent leakage of toxic chemicals such as heavy metals and hydrocarbons, then hazardous leachate contents will be an important parameter (e.g. Conner 1994). If the objective is to provide seepage cut-off, such as in cut-off walls, then (low) permeability and continuity of the cut-off structure are important parameters. However, if the objective is to stabilise soft and marginal soils for construction, then the important parameters are strength, stiffness and spatial uniformity. An important aspect of chemical soil mixing is spatial variability. Indeed, this is an important aspect which makes adequate monitoring all the more important. This issue will be discussed in more detail in this as well as in the next chapter.