Groundwater monitoring typically comprises the measurement of water levels and the recovery of water samples for laboratory analysis. For highly contaminated sites, groundwater monitoring is additionally used to determine free product (floating oil) within the groundwater or as validation work following remediation.
In some cases, where controlled waters (groundwater or surface water) are considered to be at risk of pollution a quantitative groundwater risk assessment (QGRA) may be specified. The groundwater risk assessment, frequently known as a P20, is usually requested and regulated by the Environment Agency.
Groundwater risk assessments range from direct comparison of groundwater concentrations against drinking water or environmental quality standards, through to long term groundwater monitoring and complex computer modelling. Groundwater risk assessment is used to establish an allowable level of contamination without detriment to a defined receptor; and either derive remediation measures or demonstrate the level of contaminants is of no cause for concern.