Geophysical methods and data administration in Danish groundwater mapping

initiated in the 1990s when the pressure on groundwater resources increased due to urban development and pollution from industrial and agricultural sources. In some areas, the groundwater mapping included survey drillings, modelling based on existing knowledge and geophysical mapping with newly developed methods that made area coverage on a large scale possible. The groundwater mapping that included development of new geophysical methods showed promising results, and led to an ambitious plan to significantly intensify the hydrogeological mapping in order to improve the protection of the Danish groundwater resources. In 1999 the Danish Government initiated the National Groundwater Mapping Programme with the objective to obtain a detailed description of the aquifers with respect to localisation, extension, distribution and interconnection as well as their vulnerability to pollution (Thomsen et al. 2004). This mapping programme covers around 40% of the area of Den mark designated as particularly valuable water abstraction areas. Water consumers fi nance the mapping programme by paying 0.04 € per cubic metre of consumed water. At the end of the programme in 2015, the total cost is estimated to be about 250 000 000 € with a significant part spent on geophysical mapping. The mapping programme is administered by seven local offices under the Ministry of Environment, but most of the practical work is carried out by private consulting companies, and involves the use of geophysical survey methods, survey drillings, well logging, water sampling and hydrological mapping, as well as geological and groundwater modelling. In major parts of the particularly valuable water abstraction areas, it is important to obtain spatially dense geophysical data covering large continuous areas.