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22% of drinking water produced by De Watergroep is pumped from the Chalk aquifer. To better understand the capacity of the Chalk and the impact of different users, De Watergroep, the Dutch research institute KWR and VUB start a project to contribute to sustainable groundwater exploitation. Two postdoctoral researchers from the research group of prof. Marijke Huysmans from the Department of Hydrology and Hydraulic Engineering (HYDR) of VUB will study the capacity of this aquifer - taking all different sources of uncertainty into account - in this three-year project.

 

 

 

Importance of the Chalk aquifer for water supply

 

 

 

De Watergroep produces 140 million m³ per year. 22% of this quantity is pumped from 29 locations from the Chalk aquifer, an important groundwater bearing subsurface layer in Flemish Brabant, Walloon Brabant and Limburg. This aquifer is also intensively used for industry and agriculture. The Chalk aquifer is exposed  at the surface in the north of Wallonia around the axis Waver, Waremme and the valley of the River Jeker. In this area, the aquifer is fed by precipitation and has a phreatic character. Towards the north, this layer dips into the subsurface and is covered by younger clay rich layers that give the Chalk aquifer a confined character. The layer is found at a depth of 96 m in Leuven, 226 m in Aarschot and 150 m in Hasselt. Because of this large depth, the groundwater is well protected from influences from above. Therefore, the Chalk aquifer is a strategic water bearing layer containing pure groundwater.

 

 

More data about the Chalk aquifer lead to better understanding

 

 

 

The governing parameter for groundwater flow, such as permeability and porosity, of the Chalk aquifer are spatially very variable and are only known at those locations where pumping tests have been done or where monitoring wells are present. Therefore, our knowledge about this aquifer is relatively limited. We know that permeability can very significantly, both horizontally and vertically, because of variations in fracturation and fault patterns. Because of the large depth of the aquifer, only few boreholes and data are available.

 

 

Until now, groundwater studies were mainly focusing on local scale to study a small part of the aquifer.

Therefore, De Watergroep, VUB and KWR have set up a collaboration to study the capacity of the aquifer on a regional scale and to build a decision tool to evaluation current and future pumped discharges from the Chalk aquifer. For sustainable groundwater use, it is of utmost importance that the volume of water extracted from the aquifer is not larger than its capacity.

 

 

Numerical groundwater models are classical groundwater tools to calculate scenarios. In this study, a groundwater flow model for the Chalk aquifer will be built and it will be subjected to a thorough uncertainty analysis. This complex analysis will be run on a supercomputer. The results of this uncertainty analysis will be translated into a decision tool. With this tool, different pumping scenarios can be compared under uncertainty. This study will contribute to sustainable use and management of the Chalk aquifer. The project starts in September 2018 and runs for three years.