It is important when carrying out a site investigation to determine the nature of any pollutants present in the groundwater. Regulatory authorities are likely to insist on this, particularly if the site is in close proximity to an aquifer, a source protection zone or licensed abstraction.

 (An aquifer is defined as a geological formation or group of formations containing sufficient saturated permeable material to yield significant quantities of water to wells and springs). Regulatory authorities may also require leaching tests to be carried out on samples of soil.

The purpose of these determinations is to quantify the contamination status of the groundwater, and to identify the potential for further pollution to occur by soil and water interaction, and hence assess the risks to groundwater supplies.

Contamination may have resulted from a non-replenishable one-off occurrence, eg a fuel spill, or the result of on-going pollution, eg leachate from a landfill site.