In the management of groundwater resources problems of quantity and quality cannot be separated from each other. Contaminated aquifers modelling is crucial in answering questions such as where is the contaminating source? what is the best prevention/restoration strategy? where and how should one store radioactive waste? etc. TK Consult AG modelling strategy consists of (1) analysis of existing information, (2) conceptualization of the system behavior, (3) implementation of such concept into a numerical model, (4) model calibration and (5) scenario analysis of e.g., different aquifer restoration strategies. Such methodology has been successfully applied to a large number of projects worldwide.