Denmark is a kingdom of islands. Denmark consists of more than 500 islands,<br>200 of which are inhabited, though many are smaller than 10 km2. Supplying good<br>quality drinking water for the inhabitants often presents major problems, some of<br>which are specific for the islands.<br>For geometrical reasons the coast-near regions of an island are a relatively larger<br>proportion of the total area, the smaller the island is. This means that the area, where<br>the proximity of the sea presents problems of salt water intrusion in the aquifers, is<br>relatively large, and abstraction of fresh ground water is most often precluded in these<br>parts, On the other hand, farming is the main occupation and means of living on the<br>smaller islands, so the problems with infiltration of nitrate from excess fertiliser and<br>pesticides related to agricultural use are very acute. For these reasons’ reports of<br>deteriorating water quality have appeared from many of the smaller islands.<br>There are many good reasons why the problem should be solved locally. The<br>Department of Earth Sciences has been involved in co-operative research projects with<br>several municipal water supplies in Denmark to find strategies for the application of<br>geophysical methods to solve the specific hydrogeological problems of the minor<br>islands, all of which are characterised by a Quatemary sedimentary geology.<br>An integrated use of geophysical methods has proven ifself to be very applicable<br>in the type of detailed hydrogeophysical investigations, which must be carried out to<br>provide the necessary insight into the hydrogeology of an island. This demands that<br>efficient and detailed methods for measurements and interpretations are developed,<br>and the strategic aspects of data collection and interpretation become important.<br>In this context we present results from the PA-CEP electrical profiling method<br>and the Ellog auger drilling method with undisturbed water sampling which, together<br>with transient electromagnetic soundings and geoelectrical soundings, can be<br>combined into an efficient scheme for detailed hydrogeological investigations. The<br>results of these investigations are the foundation for decisions on remediating<br>measures, sitings of new abstraction wells, and possible restrictions on the land use.


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