|(übersetzt):||The natural protection of the groundwater against contamination is given by the geological layers covering the groundwater table, the groundwater protective layers. Through these layers surface water is infiltrating leading to the groundwater recharge. During this infiltrating a cleaning of contaminated water can occur due to biological and chemical decomposition of the contaminants or due to sorption processes. The infiltration time is given by the hydraulic conductivity and the thickness of the strata overlying the aquifer. The hydraulic conductivity of a layer is inversely related to the clay content. So the clay content is a crucial petrophysical parameter for the groundwater protection. In this work an attempt is made for the assessment of the clay content of near surface material from geophysical measurements. For practical reasons the electrical conductivity was chosen for the clay content estimation.