Depending upon the findings of the initial desk study groundwater monitoring is often specified as part of the intrusive phase of the site investigation and is sometimes required as part of a long-term monitoring program or groundwater risk assessment.
Groundwater monitoring generally comprises the measurement of water levels and the recovery of water samples for laboratory analysis. For highly contaminated sites, groundwater monitoring is also 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 bodies) are considered to be at risk of pollution, a quantitative groundwater risk assessment (QGRA) may be specified. The groundwater risk assessment, commonly known as a P20, is usually requested and regulated by the Environment Agency.
Groundwater risk assessments can range from a simple comparison of groundwater concentrations against drinking water or environmental quality standards, through to long term groundwater monitoring and complex computer based modelling. The findings of the groundwater risk assessment are used to establish an acceptable level of contamination without detriment to a defined receptor and either derive remediation measures or demonstrate that the level of contaminant is of no cause for concern.