Groundwater dating

Groundwater dating to better understand the subsurface

At the Geological Survey of the Netherlands, we carry out groundwater dating. In cooperation with universities at home and abroad, we measure various stable and radioactive isotopes (also called tracers). We use them to determine the age of the groundwater, which gives us and our clients more insight into the subsurface of the Netherlands.

Age determinations to increase knowledge of groundwater

The age of groundwater refers to the period of time between the moment the water fell as rain and was drawn into the ground, until it is pumped up to a certain depth. Depending on this depth, the age of the groundwater can vary from a few months to tens of thousands of years. Groundwater is an important source of drinking water in the Netherlands. Moreover, clean groundwater is essential for the preservation of nature reserves and ecosystems. To guarantee our groundwater is of sufficient quality, both the shallow and deep groundwater in the Netherlands are constantly monitored. By determining the age of the groundwater, we increase our knowledge of the subsurface, which benefits this monitoring. The age of the groundwater is also an essential parameter in determining the speed at which dissolved substances are able to penetrate the soil. 

Groundwater age helps optimise quality monitoring networks

In the Netherlands, the quality of shallow groundwater is monitored in various monitoring networks. It is useful for the managers of these monitoring networks to know the age of the groundwater. For example, by dating the groundwater, we gain insight into how quickly pollutants can penetrate the groundwater and we can determine exactly whether the concentrations of these substances in the most youngest groundwater are increasing or decreasing. In the shallow subsurface, we determine the age of the groundwater using tritium (³H) and helium (³He). This technique allows us to determine the age of groundwater up to 100 years old. We measure the concentrations of both tritium and helium in the water and use the ratio between the two to determine the age of the water. We can then use these ages to calculate trends in groundwater quality, which is an important purpose of the monitoring networks.

Groundwater ages help determine the vulnerability of drinking water supplies

Besides this shallow and relatively young groundwater, we also calculate the age of deeper, older groundwater. This deeper groundwater is used, among other things, to make drinking water. For drinking water companies, it is essential to know how vulnerable their sources are to potential contaminations. For this, the age, and thus the speed at which the groundwater moves, is a highly important parameter. In general, drinking water extraction sites attract a mix of different groundwater types. We determine the age of this mix using various tracers. For example, the amount of tritium says something about the proportion of young water up to about 100 years. We use an isotope of argon (³⁹Ar) for the proportion of water aged 50 to 1,000 years, and carbon-14 and helium-4 for the oldest water up to 100,000 years. By properly characterising this mix, we are able to estimate the vulnerability of the drinking water extraction sites. After all, in drinking water extraction sites in which the water is relatively young,  harmful substances can reach the source more quickly than in places where the water is very old. By assessing this properly, we are helping water companies to guarantee the good quality of future drinking water.

Would you like to receive more information? Contact Hans-Peter Broers via the blue button below with the ‘mail directly’ label.

Relevant publications

• Broers, H.P. 2004. The spatial distribution of groundwater age for different geohydrological situations in the Netherlands: implications for groundwater quality monitoring at the regional scale. Journal of Hydrology  299(1-2), pp 84-106. https://doi.org/10.1016/j.jhydrol.2004.04.023
• Visser, A., Broers, H.P., van der Grift, B., Bierkens, M.F.P. 2007. Demonstrating trend reversal of groundwater quality in relation to time of recharge determined by ³H/³He. Environmental Pollution 148(3), pp 797-807. https://doi.org/10.1016/j.envpol.2007.01.027
• Visser, A., Broers, H.P., Purtschert, R., Sültenfuß, J., de Jonge, M. 2013. Groundwater age distributions at a public drinking water supply well field derived from multiple age tracers (⁸⁵Kr, ³H/³He, and ³⁹Ar). Water Resources Research 49(11), pp 7778-7796. https://doi.org/10.1002/2013WR014012
• Broers, H.P., Sültenfuß, J., Aeschbach, W., Kersting, A., Menkovich, A., de Weert, J., Castelijns, J. 2021. Paleoclimate Signals and Groundwater Age Distributions From 39 Public Water Works in the Netherlands; Insights From Noble Gases and Carbon, Hydrogen and Oxygen Isotope Tracers. Water Resources Research  57(7). https://doi.org/10.1029/2020WR029058
• Kivits, T., Broers, H.P., Beeltje, H., van Vliet, M., Griffioen, J. 2018. Presence and fate of veterinary antibiotics in age-dated groundwater in areas with intensive livestock farming. Environmental Pollution  241, pp 988-998. https://doi.org/10.1016/j.envpol.2018.05.085