It is important to understand at the outset the natural hydrochemical conditions that exist in aquifer systems, as these provide the necessary baseline from which quality changes caused by human impacts can be determined. The natural hydrochemical conditions may also affect the behaviour of some pollutants. Because groundwater movement is typically slow and residence times long, there is potential for interaction between the water and the rock material through which it passes. The properties of both the water and the material are therefore important, and natural groundwater quality will vary from one rock type to another and within.
