FRESHMAN researches use of brackish groundwater as new drinking water source

Dunea is carrying out the FRESHMAN project in collaboration with KWR, circular innovator Allied Waters, and the Flemish drinking water utilities De Watergroep and Aquaduin. Over the last year a wellfield and pilot installation were created in Scheveningen. A replica pilot later will follow in Avekapelle, Belgium. The commissioning of the pilot installation marks the beginning of a three-year research period, during which Dunea will be pumping up brackish groundwater from under the freshwater lens in the dunes, and then treating it to produce fresh drinking water. In the process, the impact on the groundwater, such as a change in the distribution of fresh, brackish and saline groundwater, and the growth in the freshwater lens, will be closely monitored. The FRESHMAN project has been made possible by the European LIFE programme, and builds upon research carried out within the COASTAR knowledge programme.

Strategic abstraction of brackish groundwater

Dunea produces drinking water by infiltrating pre-treated river water in the dunes and then pumping it up again following dune passage. The freshwater lens floats above saline groundwater, with a brackish transition zone between them. This brackish groundwater is a suitable source for drinking water once it is desalinated. By strategically abstracting the groundwater, at the right depth and location, the freshwater supply can grow. In this way, Dunea kills two birds with one stone: it obtains a new, extra source of drinking water and a larger supply of freshwater in the dunes for periods of scarcity.

Geohydrological research

Teun van Dooren, a geohydrologist at KWR, contributed to the design of the wellfield, and now heads the geohydrological research on the abstraction of brackish groundwater. ‘The abstraction well for brackish groundwater has filters at three different depths in the brackish transition zone. These filters can be controlled independently, so that we can abstract brackish water of the desired quality in a very targeted manner. In the next few years, we will learn which settings permit us to optimally expand the freshwater lens and to deliver brackish water of constant quality to the treatment process.’

Best measured groundwater pilot

The pilot is equipped with several innovative measurement techniques that enable very close monitoring of the distribution of fresh, brackish and saline groundwater. Among these techniques is crosshole ERT, a geophysical method that compiles a three-dimensional image of the distribution of fresh, brackish and saline groundwater around the abstraction well. Researchers at the Deltares knowledge institute designed this system and will be carrying out the measurements and analyses in the years ahead. Teun van Dooren (KWR): ‘This is one of the best measured groundwater pilots in the world. A true geohydrological playground, where we are going to learn a great deal about the flows of fresh, brackish and saline groundwater.’

Wim Drossaert, CEO at Dunea, starts up the reverse osmosis installation which purifies the brackish groundwater into drinking water. Water technologist Franca Kramer (Dunea) leads this part of the research.

Drinking water production 2030

With this pilot Dunea is exploring its options for drinking water production after 2030. Because of the growth in population, the utility’s annual drinking water production will have to increase from 85 million m³ in 2020, to about 95 million m³ in 2030, and to more than 100 million m³ in 2040. ‘We have a process that is becoming increasingly vulnerable to climate change, pollution and construction ambitions that affect our vital infrastructure,’ explains Dunea’s CEO Wim Drossaert. ‘Our response is a multi-source strategy: more sources, closer to home, making use of different treatment techniques. In this way we will be able to continue supplying enough drinking water under all kinds of conditions.’

Stakeholder process

Whether brackish groundwater will really become a drinking water source after 2030, will depend not only on the success of the FRESHMAN project but also on the outcome of the stakeholder process. Drossaert: ‘This should be done carefully. That’s why we are going to begin discussions with the stakeholders this year, and why we’re studying the impact of different solutions on the environment. In the meantime, the FRESHMAN research continues. After all: without research, they’re no options.’

Geohydrologist Teun van Dooren (KWR) next to the abstraction well at the brackish water pilot. Brackish groundwater is abstracted from a depth of 90 to 110 meters, directly under the freshwater lens. To the left in the picture, Gertjan Zwolsman (Dunea), LIFE FRESHMAN project coordinator.