A new paper has proposed an approach to develop the first voluntary Groundwater Watch List (GWWL): an initiative with which to identify, monitor, and characterise substances that have the greatest potential to pollute this water resource.

Groundwater is an important element in the Water Framework Directive (WFD) 2000/60/EC and its daughter directive on groundwater 2006/118/EC which aimed to achieve the WFD objective of “good” chemical status for groundwater by 2015. The daughter directive introduced, for the first time, quality objectives obliging Member States to monitor and assess groundwater quality on the basis of common criteria and to identify and reverse upward trends in groundwater pollution.

However, over the past two decades, concern has also grown about the occurrence of anthropogenic organic contaminants in the environment, such as substances used in pharmaceuticals, food production and manufacturing. Many of these compounds are not sufficiently monitored or regulated in groundwater.

The paper proposes GWWL ranking and a selection process involving the following steps. It relies on aggregate data (data combined from different measurements) from national agencies across Europe on substance occurrence, persistence, mobility and potential toxicity and bioaccumulation behaviour.

  • Substances are initially identified based on either exposure risk (their theoretical leaching potential, mobility, persistence or extent) or existing monitoring data (their proven presence in groundwater).

  • Substances are then given a “groundwater leaching score”, and identified as either a toxicological or ecotoxicological hazard.

  • If sufficient monitoring data are available, the substances are deselected and added to a list with which to inform other relevant GWD annexes.

  • If sufficient monitoring data are not available, the substances are added to the new GWWL.

  • Substances on the GWWL are then prioritised based on their identified toxicity risk.

  • Those posing the highest risk are monitored until data are sufficient for them to be removed from the GWWL.

The authors recommend that this data will inform evidence-based decisions on which substances to include in priority lists.

Last reviewed 13 February 2020