Hydrogeological mapping as a basis for establishing site-specific groundwater protection zones in Denmark

The water supply in Denmark is based on high-quality groundwater, thus obviating the need for complex and expensive purification. Contamination from urban development and agricultural sources, however, increasingly threatens the groundwater resource. In 1995 the Danish Government thus launched a 10-point plan to improve groundwater protection. In 1998 this was followed by a decision to instigate spatially dense hydrogeological mapping of the groundwater resource within the 37% of Denmark designated as particularly valuable water-abstraction areas. The maps will be used to establish site-specific groundwater protection zones and associated regulation of land use to prevent groundwater contamination. Traditional mapping based solely on borehole data is too inaccurate for this purpose. The work will take 10 years and cost an estimated DKK 920 million, equivalent to 120 million euro (E). To fund this, consumers will pay a E 0.02 surcharge per m(3) of drinking water during the 10-year period. This review of the Danish strategy to protect the groundwater resource demonstrates why dense mapping with newly developed geophysical measurement methods in large contiguous areas accords geophysics a highly central role in the forthcoming hydrogeological mapping. It is illustrated by examples of spatially dense, large-scale geophysical mapping carried out in the Aarhus area.