Over the past 20 years there has been an intensive effort to map the groundwater reserves in Denmark. This has been achieved through test wells and the gathering of geophysical data (seismic and electromagnetic methods), together with pumping tests and chemical analyses of the water. These investigations have largely been financed by taxes on water consumption. The purpose has been to locate reserves of groundwater, to establish how well they are protected against pollution, and to determine their quality. The overall aim has been to secure drinking water reserves for the future by identifying areas where some kind of protective action is required. The Engbjerg area has been subjected to these studies so that a wide range of geological, hydrological and water chemical data is available.
In the Miocene epoch (about 24 to 5 million years ago), the distribution of land and sea changed in Denmark because of climatic variations, changes in the sediment supply and subsidence of the North Sea Basin. The coastline moved back and forth across Denmark and the Engbjerg area changed from being near the coast to relatively deep seawater. During deep water periods marine clay was deposited, whereas during shallow water times it was marine sand. A series of sediments alternating from clay-rich (the Vejle Fjord, Klintinghoved and Arnum Formations) to sand-rich (the Billund, Bastrup and Odderup Formations) developed.