Nitrate pollution of shallow aquifers is still one of the main problems that endanger drinking water supply in rural areas with a high impact of agricultural fertilization. Five test sites, spread over the whole of Flanders, each with 8 multi-level wells, have been installed in the scope of a project of the Flemish government (AMINAL) for detailed research about mechanisms of nitrate pollution and nitrate removal in Flemish sandy aquifers. The sites are located in different hydrogeologically homogeneous zones. These zones, mapped on a scale of 1:50,000, indicate areas of Flanders with comparable hydrodynamical and hydrogeochemical boundary conditions of the phreatic aquifers. Five of the most important zones have been chosen for the installation of the test sites.