Ecosystems and the quantity and quality of water resources are under severe pressure globally. The EU responded with its Water Framework Directive1, which aims to reverse pollution and clean up EU water bodies by 2015. BRIDGE2 was established to develop and test a methodology to derive groundwater threshold values, and support the development of a common methodology for EU Member States.
The 14 groundwater bodies investigated in BRIDGE were selected to represent as many aquifer types, climate settings and European ecoregions as possible within the project group that included partners from 17 EU countries. Some of the groundwater bodies are known to interact with associated ecosystems, while others do not.
BRIDGE has developed an approach and methodology that uses two different environmental quality standards. These are for:
- dependent aquatic ecosystems, and
- groundwater 'itself'
In the latter case, groundwater is protected as an ecosystem 'itself' or as a source of human water supply for the protection of human health. Little is known about water quality needs of groundwater ecosystems, so surface water quality standards (EQS) or drinking water standards (DWS) are sometimes used instead.
The researchers compared derived groundwater threshold values for dissolved chlorine and arsenic using drinking water standards as reference values for all 14 case studies. They also carried out more detailed analyses for the Odense Pilot River Basin (Denmark) and the Vouga River Basin (Portugal), where they derived groundwater threshold values for these and five further elements, including the nutrients nitrogen and potassium, based on environmental objectives and quality standards for groundwater dependent ecosystems.
The thresholds are derived using relevant reference criteria, such as natural background levels, environmental quality standards and drinking water standards. The study results demonstrate that the proposed methodology is operational and may be used to protect human health and the environment. Furthermore, the results also show that for some pollutants (e.g. nitrate) and catchments, groundwater threshold values for safe drinking water (drinking water standards) are not low enough to meet environmental objectives and safeguard dependent ecosystems.
The research has shown that developing environmental quality standards for groundwater 'itself' is in its infancy. Much more research is needed to develop and apply this concept appropriately and efficiently; more data on groundwater and groundwater interaction with dependent ecosystems are also needed. Properly designed monitoring programmes and compliance guidelines considering groundwater and surface water as one resource are just as important as properly derived groundwater threshold values to protect human health and the environment.