Groundwater of good quality

Improve or maintain groundwater quality with well-founded measures

Thanks to its predominantly good and stable quality, groundwater is one of the most important freshwater resources in the Netherlands. However, the quality of this groundwater is under growing pressure. Drinking water utilities are reporting contaminants more often and in increasing numbers in their abstraction wells. Historical contaminants reach the wells after transport times ranging from years to decades. Provincial groundwater measurement networks show that these problems will persist for the time being. Meanwhile, emerging substances, such as PFAS, are on their way. Although there is currently no clear picture of the risks these new contaminants represent, there is reason for concern about the future groundwater quality. Typically, when it comes to groundwater quality, the problems and their causes can vary significantly from one place to another, and the effects of contaminants on the groundwater often only become apparent after lengthy periods of time. Maintaining the good quality of groundwater and, when necessary, improving it, are among the objectives of the Water Framework Directive (WFD).

Determining the behaviour of substances in the soil and water system

At KWR we conduct research into the occurrence and behaviour of substances in the soil and water system. Emerging contaminants like PFAS receive special attention, along with the known contaminants like pesticides and nitrate. KWR has extensive knowledge about the behaviour of contaminants in soils and the groundwater. Do contaminants become immobilised or not? Do contaminants degrade, and is that positive, or does it mean that other contaminants are formed that we would rather not have in the environment? We draw on this knowledge to assess the risks, for example, for drinking water resources, and to devise solutions. Can we use the soil and the subsurface in such a way that the infiltrating water is optimally treated, and thus makes a positive contribution to the water supply?

Methods, tools and products

PFAS and other micropollutants

Per- and polyfluoroalkyl substances (PFAS) are very stable compounds that can accumulate in our environment. For drinking water utilities, it is important to know what they can expect at their wells if there are PFAS sources present in the abstraction area. At KWR we develop knowledge about the behaviour of PFAS in soils and the subsurface, and the risks to drinking water abstraction, as elaborated in the Kennisdocument (in Dutch) on the behaviour of PFAS in the soil. We do model studies of the specific behaviour of PFAS and other micropollutants in the saturated and unsaturated zone. Using the AquaPriori-Bodem tool, we conduct quick analyses of the removal during soil passage of (new) organic micropollutants, and of the breakthrough of these substances into abstraction wells. AquaPriori-Bodem will soon be included in the Risicotoolbox Grondwater (Groundwater Risk Tool Box) of the RIVM (Dutch National Institute for Public Health and the Environment).

Responsible infiltration

The active infiltration of (surface) water can contribute to a more resilient regional freshwater supply, provided the groundwater quality does not deteriorate. Under a commission from STOWA, KWR wrote a Deltafact report (in Dutch) on the impact of artificial infiltration of surface water on groundwater quality; a second report will be produced shortly on responsible infiltration and its effects on groundwater quality. In the KWR laboratories we use a Micro-Oxymax respirometer to study the oxygen consumption and CO2 production of sediment samples, with the aim of determining how reactive the soil is over time and which soil components are reactive. This allows us to characterise the number and intensity of chemical transformation processes in sediment samples, and to obtain a better understanding of the development of the groundwater quality.

Groundwater protection

In addition to research into responsible infiltration, KWR also uses other instruments to protect the soil and groundwater, prevent undesirable impact on groundwater quality, and enable safe drinking water production alongside land use for other purposes. Our policy-support research underpins groundwater protection measures while also identifying problem areas. In addition, KWR develops new concepts for groundwater protection based on the motto ‘protect to preserve’. We examine the conditions under which the surface and subsurface can be used within the frameworks for a future-proof drinking water supply. Finally, KWR develops techniques for environmental forensics, in order to trace contaminants back to their source and thus assist in tackling the source.

Projects

  • There is still an important research gap as regards the transport of PFAS in the subsurface. We recently conducted an exploration (in Dutch) of the leaching of diffuse PFAS for unsaturated soils. We used both an analytical and a numerical tool to calculate PFAS leaching and subsequently compared the outcomes. A follow-up project is now underway. 
  • The latest WFD evaluation revealed that the various drinking water resources are still under pressure from plant protection products (PPPs). In groundwater abstractions from semi-confined aquifers, that are less well protected by a clay layer, several PPPs are still regularly detected above the standards. We are currently doing policy-support research for Vewin, with the objective of providing a current overview of the prevention of PPPs in drinking water wells on the basis of measurement data and survey reports. 
  • Under a commission from STOWA, we published a Deltafact report (in Dutch) on the effects of artificial infiltration of surface water on groundwater quality. The report also contains an overview of the legal and policy framework which applies to artificial infiltration