Groundwater protection: vulnerability of aquifers

The protection of groundwater reservoirs is given by the covering layers, also called protective layers. Surface water percolates through the protective layers leading to groundwater recharge. During this percolation process contaminant degradation can occur by mechanical, physicochemical, and microbiological processes. An effective groundwater protection is given by protective layers with sufficient thickness and low hydraulic conductivity leading to high residence time of percolating water (Fig. 18.1). In the following, protective layers are regarded as homogenous bodies which can be characterized by bulk properties like hydraulic conductivity. Inhomogeneities as sandy intrusions or fissures in clay which can lead to preferred pathways for percolation are not taken into account, although they are quite common (Douma et al. 1990).