The PhD research of Martijn van Leer has the objective to improve the parameterisation of the hydraulic conductivity of aquitards. How can pumping tests be used understand the spatial variability of the hydraulic conductivity? What are the main drivers defining the hydraulic conductivity in these aquitards? How can regional extraction data be used to gain insight in the properties of an low permeable layer, even at locations with less available data? Groundwater flow models and (geo-) statistical methods are used to answer these questions. The research project is a collaboration between Utrecht University and TNO - Geological Survey of the Netherlands.