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Udpegningen af grundvandsforekomster i Danmark

Summary and conclusions

The designation of groundwater bodies is a central part of the baseline analysis according to the Water Framework Directive (WFD). In Denmark, the baseline analysis according to WFD article 5, has been carried out by 12 water authorities at county level. The delineation of groundwater bodies has been based on hydrogeological mapping, but due to geological variations, different levels of mapping and different methods of identifying groundwater bodies, the size and shape of groundwater bodies varies so much that they cannot serve as the basis of the future monitoring, assessment of status and establishment of the programme of measures, according to the WFD.

As a result of the municipal reform taking place in Denmark on January 1st 2007, the water authority will, from this date, be the state, and the number of River Basin Districts (RBDs) will be reduced to four. Hence, the state is responsible for the elaboration of the monitoring programme according to the WFD which has to be established before December 22, 2006. The Danish Environmental Agency has therefore initiated a project with the objective of revising the groundwater bodies to conform to the needs. The project has been carried out in close collaboration with representatives of the water authorities.

Phase one of the project aims to analyse and describe the groundwater bodies designated and to establish three different models for revising them. This report describes the results of the first part of phase one; the analysis and description of the groundwater bodies in Denmark, designated in the baseline analysis.

As a basis of the investigation, the reporting of the baseline analysis from all water districts was collected. The written reports were at very dissimilar, varying from metadata to comprehensive reports. Furthermore, GIS-files produced in different systems were reported. All accessible information about the groundwater bodies was systematised and filled into forms to facilitate the comparison. Nine counties were visited and interviewed to complete the information, and to discuss the possibilities and possible problems in different models of revision. The statistics of the groundwater bodies are shown in the table below.

Number and size of groundwater bodies in each River Basin District

The total number of groundwater bodies in Denmark is more than 1900, but the number in each RBD varies from only three to more than 1400. Accordingly, the average size of the groundwater bodies varies by two decades. For two RBDs, it was not possible to calculate the average size of the groundwater bodies, as district no. 55 has not produced maps of the total size of each groundwater body, and district no. 76 has not delineated groundwater bodies. Thus, the numbers are missing in the table. The number provided (3) refers to the three levels where aquifers were mapped.

Although the difference between RBDs is great, it is also worth noting that the size of groundwater bodies varies remarkably within each RBD, and only two RBDs have not designated groundwater bodies less than 4 km². Some of the smallest groundwater bodies are found as aquifers on small islands, but in some districts aquifers only found in one well were used to define a small groundwater body if it was not possible to correlate with other wells.

The definition of groundwater bodies was handled in different ways in each river basin district, and although some have used methods that at first glance appear to be similar, the results may be very different. A major part of the differences can be explained by geological variations, as some parts of the country has primary aquifers in regional limestone aquifers or tertiary sand, whereas other parts only have aquifers in alluvial sand embedded in till.

Most districts have divided aquifers into two or three levels; shallow, medium or deep groundwater bodies, but the limits used are different; some have used geological criteria, others e.g. depth below the groundwater table. Some groundwater bodies were defined in three-dimensional geological models where the layers were defined as geological facies; others used gridded pixel models. This often results in lack of continuity across the borders.

Most of the water authorities have described certain problems assessing the status of the groundwater bodies, or rather assessing whether the groundwater bodies will achieve good status in 2015 as required in the WFD. Districts no. 76 and 80 had to sub-divide the groundwater bodies to assess the chemical status, and quantitative status was assessed in river basins instead of groundwater bodies. Very large groundwater bodies have caused problems too, as findings of pollution in parts of the groundwater body and observation wells without quality problems in other parts, tell different stories.

Furthermore, there is often a discrepancy between the status reported in the WFD baseline analysis and the results of the detailed hydrogeological mapping and elaboration of action plans which is carried out in all water abstraction areas in Denmark these years.

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Version 1.0 Marts 2007, © Miljøstyrelsen.