On the site of a former ammunition factory in Hessisch-Lichtenau/Hirschhagen in northern Hesse, a large number of boreholes and groundwater monitoring wells were installed as part of a remediation and containment plan. Hydraulic testing over a period of 20 years has significantly improved the understanding of the hydrogeological system. The alternating sandstone, siltstone and claystone formations of the Middle Buntsandstein at the site constitute a succession of aquifers, semi-pervious layers and aquicludes. The subsurface is fractured by step faults and is also permeated by tectonic faults and fissures. This results in a heterogeneous, anisotropic system in which water circulates primarily through permeable fault zones. The aquifer consists of three different zones that are connected through preferential pathways along fault lines. The Upper Zone (Hirschhagen) and the Intermediate Zone are perched aquifers that enable groundwater seepage to lower aquifers. In all three zones, preferential flow paths were observed along north-south striking fault lines.