Groundwater chemical status

© Francisco Javier Domínguez García, WaterPIX EEA2

Groundwater provides a major source of drinking water for many EU citizens as well as the steady base flow of rivers and wetlands. Maintaining this flow and keeping it free of pollution is vital for both humans and surface water ecosystems

Introduction

Groundwater provides a major source of drinking water for many EU citizens and provides the steady base flow of rivers and wetlands. Keeping groundwater free of pollution is vital for humans and river and wetland ecosystems. Once pollutants are in groundwater, recovery can take years or even many decades because of residence times and the slow degradation of pollutants.

Do you know?

In the EU, around 75 % of the groundwater body area is in good chemical status

In total, 160 pollutants caused failure to achieve good chemical status

Nitrate is the most common pollutant causing failure to achieve good groundwater chemical status. It affects 18 % of the groundwater area

Nitrates in groundwater are linked to sustained pressure from agriculture and long recovery times

Groundwater chemical status

FIGURE 1

Assessment of chemical status or potential of groundwater bodies

Source: European waters. Assessment of status and pressures 2018. EEA Re. port No 7/2018

To achieve good groundwater chemical status, EU member states and Norway assess their groundwater bodies according to four criteria:

  • Concentrations of pollutants do not exceed the standards set for groundwater
  • Absence of saline intrusion in the groundwater body
  • Pollution levels must not impact ecological or chemical status of surface waters
  • Pollution levels must not cause significant damage to ecosystems and wetlands that depend directly on the groundwater body.

Concentrations must comply with EU standards for nitrates and pesticides, and with national threshold values for other groundwater pollutants. EU standards for nitrates is 50 mg/l and for pesticides it is 0.1 μg/l for individual pesticides and a total maximum 0.5 μg/l. Threshold values for other pollutants can be set at the level of the groundwater body, national river basin or international river basins. In part this flexibility is necessary due to the variability in concentration of naturally occurring substances. Furthermore, some substances in groundwater may be of natural origin, e.g. when the bedrock contains high concentrations of metals and salts, and as such they are not considered pollution.

Chemical status assessments of groundwater are performed by all EU Member States every 6 years, in 2009, 2015, and 2021. On the scale of Europe, around 75 % of the groundwater body area is in good chemical status, 24 % failed achieving good chemical status, and 1 % is in unknown status (FIGURE 2). The overall groundwater chemical status has not improved since 2009.The results of the 2021 assessments are not yet known.

FIGURE 2

Chemical status of groundwater bodies

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FIGURE 3

Proportion of groundwater bodies in RBD failing to achieve good chemical status

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Pressures on groundwater chemical status

EU Member States and Norway reported a total of 160 chemicals causing poor chemical status. The list of substances most frequently leading to groundwater body poor chemical status is dominated by nitrates and pesticides used in agriculture and arising from salt intrusion. In addition, some industrial chemicals lead to failure, such as tetrachloroethylene, used as a solvent, and metals such as arsenic, nickel and lead, which arise from, for example, mining, contaminated sites and waste water.

Nitrates are reported as the reason for failing to achieve good groundwater status by 24 countries, and in 18% of the groundwater area. Pesticides also commonly cause failure and affect 6.5% of the groundwater area. Nitrates and pesticides are extensively used in agriculture and reach groundwater through diffuse pollution. Where fertilizers, manure and pesticides are applied to crops in excess, they present a significant and widespread challenge.

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References

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Related Resources

Groundwater chemical status in Data, maps and tools section

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