Lowering of the ground water table - does it affect the fresh/salt water interface, and can we measure it?

Abstract

The Danish supply of potable water is mainly based on ground water. During construction work in areas with a shallow ground water table, temporary lowering of the water table is often necessary. In coastal regions, if the lowering of the water table is close to existing water abstraction sites, the ground water quality can be threatened by changes in the depth to the freshwater/saltwater interface. With an example from Vestamager near Copenhagen, Denmark a combination of geophysical methods for monitoring the freshwater/saltwater interface is demonstrated. The example ilustrates the advantages of combining geophysical well logging in observation wells with time domain electromagnetic (TDEM) soundings.