According to Austrian Standard B 2400, the terms deep groundwater and multi-aquifer formation are defined as follows: Deep groundwater is groundwater in the deeper layers of the earth's crust, which has an extensive overburden of overlying layers, a long residence time and usually special physical-chemical properties. Deep groundwater is usually confined or artesian. A multi-aquifer formation is defined as an aquifer that is separated from overlying and/or underlying aquifers by comparatively low-permeability soil or rock layers. Groundwater aquifers may differ from each other in terms of pressure level and/or mineralization. The first groundwater level is the aquifer closest to the ground surface. Seismic reflection surveys are particularly suitable for exploration and description from the second groundwater level and thus for prospecting deep aquifers. With the help of seismic refraction, usually in combination with geoelectrics, the first groundwater level can be described in its depth position as well as its composition (grain size distribution).