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

Abstract

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 (€). To fund this, consumers will pay a € 0.02 surcharge per m³ 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.

Résumé

L’alimentation en eau au Danemark suppose une haute qualité des eaux souterraines, en éliminant ainsi le coûteux processus d’épuration. Néanmoins, la qualité des sources souterraines est menacée par la pollution provoquée par le développement urbain et agricole. En 1995 le gouvernement danois a lancé un plan en 10 points pour améliorer la protection des eaux souterraines. En 1999 ce plan a été suivi par la décision de promouvoir une cartographie hydrogéologique à grande densité sur 37% du territoire du Danemark où se trouvent des zones de captages importantes. Les cartes seront utilisées pour établir les zones de protection des eaux souterraines, en tenant compte des conditions locales du site ainsi que des règlements conjoints d’utilisation des territoires, afin de prévenir la pollution des eaux souterraines. La cartographie traditionnelle, basée seulement sur les données des forages, est trop imprécise pour ce but. Les travaux vont durer 10 ans avec un coût estimé à 120 millions d’euros (€). Pour ces travaux les consommateurs vont payer une surcharge de € 0.02 par m³ d’eau potable, ceci pendant 10 ans. Cette révision de la stratégie du Danemark concernant la protection des ressources en eaux souterraines a démontré les raisons pour lesquelles on a accordé un rôle central aux nouvelles méthodes géophysiques dans la future cartographie hydrogéologique de vaste régions. On présente un exemple de cartographie géophysique réalisée dans la région d’Aarhus.

Resumen

El abastecimiento de agua en Dinamarca está basado en agua subterránea de alta calidad, evitando de esta manera la necesidad de una purificación compleja y cara. Sin embargo, la contaminación a través del desarrollo urbano y de fuentes agrícolas, ha incrementado la amenaza para el recurso de agua subterránea. Entonces en 1995 el gobierno lanzó un plan de 10 puntos para mejorar la protección del agua subterránea. Este fue seguido en 1998 por la decisión para promover una cartografía hidrogeológica espacialmente detallada, para el recurso agua subterránea dentro del 37% de las áreas de extracción consideradas por Dinamarca con una importancia especial. Los mapas serán usados para establecer zonas específicas de protección para puntos de agua subterránea y una regulación asociada al uso del territorio, para prevenir la contaminación del agua subterránea. La cartografía tradicional basada exclusivamente en datos de la perforación es muy inexacta para este propósito. Este trabajo tomará 10 años y costará aproximadamente DKK 920 millones, equivalentes a 120 millones de Euros (€). Para financiar esto los consumidores pagarán un sobreprecio de € 0.02 por m³ de agua potable durante un periodo de 10 años. Este análisis de la estrategia Danesa para proteger el recurso agua subterránea, demuestra porque la cartografía detallada, hecha con nuevos avances en métodos de medición geofísica, aplicados a grandes áreas aledañas, otorgan a la geofísica un papel altamente importante en el futuro de la cartografía hidrogeológica. Esto está ilustrado con ejemplos de cartografía geofísica a gran escala y espacialmente detallada, llevados a cabo en el área de Aarhus.

Appendix

Chronology of Dense Hydrogeological Mapping in Denmark

• December 1998: the Danish Parliament decided that the County Councils should be responsible for detailed mapping of the water resources within a combined area equivalent to 37% of Denmark.

• August 1999: the County Councils established a technical advisory group responsible for coordinating the groundwater protection scheme. Three subgroups were established to solve practical problems within geophysical mapping, hydrological modelling and geochemistry respectively. The County Councils signed a five-year contract with the Department of Geophysics, University of Aarhus, called HydroGeophysics Group, to enhance geophysical data acquisition and interpretation through workshops and the development of improved quality assurance procedures for measurement of geophysical data, data processing, modelling and analysis software. See the website http://www.hgg.au.dk

• March 2000: the County Councils signed a contract with the Geological Survey of Denmark and Greenland for constructing and managing the national geophysical database. The mapping data can be transferred to and from the database via Internet. Together with the software company NetNord, Aarhus County Council, the University of Aarhus, the Geological Survey of Denmark and Greenland and the Spatial Planning Department developed the geophysical database system known as GERDA. See the website http://gerda.geus.dk

• May 2000: the County Councils signed a contract with the Geological Survey of Denmark and Greenland to provide instruction in the use of hydrological modelling. See the website http://vandmodel.dk/

• June 2000: the Minister for the Environment issued a statutory order stipulating how the County Councils are to implement the groundwater protection scheme (Danish EPA 2000a).

• August 2000: the Danish EPA published guidelines for the detailed mapping work and establishment of groundwater protection zones (Danish EPA 2000b).

• 2001: the County Councils established action plans including a timetable for implementing the measures necessary to protect the groundwater.

• 2000–2010: detailed mapping and groundwater protection plans to be developed for 37% of Denmark.

• 2000–2015: EU Water Framework Directive to be implemented.

• 2001: the County Councils signed a five-year contract with the Department of Geology, University of Aarhus, to ensure development of new methods, among other things for the identification of Quaternary melt-water sediments.

The EU Water Framework Directive

In summary, the new Directive

• protects all waters—rivers, lakes, coastal waters and groundwaters,

• sets ambitious objectives to ensure that all waters meet “good status” by 2015,

• sets up a system of management within river basins,

• ensures reduction and control of pollution from all sources such as agriculture, industry, urban areas, etc.,

• ensures active participation of all stakeholders, including local communities, in water management activities, and

• requires water-pricing policies and ensures that the polluter pays.