A brief general description of the characteristics of groundwater sources for most of the EU member countries is contained in the report ‘groundwater quality and quantity in Europe’, by the European Environmental Agency (EEA), June 1999, and its quoted in the following paragraph :
The Austrian groundwater areas cover nearly one third of the national territory. Groundwater in karst areas, 15,000 km2 in extent (18% of national territory), and groundwater in porous media, 10,000 km2 in extent (12% of national territory), form the most important groundwater resources of Austria. In addition, there is single productive crevice groundwater in the Central Alps, Bohemian Chain and in the borderland of the alpine region, and some larger areas with artesian and deep groundwater in Upper and Lower Austria, Burgenland, Styria and in alpine valleys.
Three types of groundwater region can be distinguished. Experts estimate that 30% of these regions are situated in porous media, <10% in karst media and about 60% in other media.
The groundwater potential in Greece is around 10,300 mio m3/year, whilst 7,400 mio m3/year is karst groundwater. Spring water is considered as surface water and is, therefore, not included in the groundwater potential.
Groundwater resources are situated in two main areas. In the late Quaternary hyaloclastites and basaltic lavas there are 40,000 km2 highly permeable and deep aquifers, an area that represents 35% of the national area. The other aquifers are more superficial with low permeability, and lie in tertiary and early quaternary basaltic lavas. The extent of these aquifers is about 60,000 km2 – about 45% of the national area.
The total area of the Republic of Ireland is around 70,000 km2. The geological structure of Ireland consists of Precambrian schists and quartzites, Devonian sandstone, Carboniferous limestone and some smaller formations. The only widespread aquifers with intergranular permeability are in the quaternary deposits. Irish aquifers are relatively shallow and often small in their lateral extent. In the western parts of the country there are karst aquifers. In Ireland the total aquifer is estimated to be of the order of 18,870 km2. It has not been possible to give a detailed breakdown by type.
It has been estimated that more than 50% of groundwater resources are in porous media, 157,244.86 km2 in extent. Groundwater aquifers in karst media extend over 50,615.11 km2 (i.e. 16.76% of national territory) and finally there are smaller groundwater resources in volcanic rock media with an area of 13,488.78 (i.e. 4.46% of national territory).
The Netherlands is a densely populated country covering an area of 38,000 km2. It is heavily industrialized and the agricultural use of soils is one of the most intense in the world. Because of the wide use of land there are great problems of groundwater pollution over large areas, especially sandy regions, covering about 42% of the whole country. In more than 90% the country groundwater level is less than 4 m below the surface level. Only in the central hills formed by glaciers can a deeper level be measured.
In Norway there are two main types of aquifer: bedrock without primary porosity but with secondary passages such as joints, and other fractured or Quaternary superficial deposits with primary porosity.
Bedrock aquifers: with the exception of the upper Permian aeolian sandstone in Brumunddal and some Permian volcanic rocks, all Norwegian bedrock types lack primary porosity and are non-permeable on a small scale. The presence of groundwater is restricted to joints formed by tectonic fracturing, and to a lesser extent, to open fractures and voids formed by dissolution of limestone and vein and void minerals, usually calcite. The abundance of water bearing fractures and the frequency of open joints (fissures) are strongly controlled by rock type (competency), thickness and type, and orientation of paleo stress and recent stress. These factors also control the actual fracture pattern and strongly influence topography.
Quaternary aquifers: The Quaternary deposits represent a very good aquifer in ice-margin deltas and in glacio-fluvial valley fills. Wells can produce water quantities in the order of ten to a hundred times higher than bedrock wells. Several cities, towns and other rural sites, as well as industrial enterprises use good water from aquifers in Quaternary deposits. The groundwater in fluvial aquifers in the valleys is infiltrated from rivers and is of good quality, with groundwater characteristics and stable temperature. The deposits can be regarded as large natural filters. The yield of wells in such aquifers may sometimes give about 100 l/s.
In Portugal the main aquifer systems are in porous media and karst. The area of porous media covers 26,000 km2 (i.e. 29.4% of national territory), karst groundwater comprises an area of 5,500 km2 (i.e. 6.2% of national territory). The aquifer systems are located in meridional and occidental Mesocenozoic border and tiercearies basin of Tejo and Sado. The average productivity is between 10 and 30 l/s per well. Almost 40% of these aquifers have a productivity of more than 30 l/s. In general the unconfined aquifers have a higher or moderate vulnerability. Some other aquifers are located in residual soils of ancient rocks, e.g. igneous or metamorphic formations, which are important local resources. The productivity of these aquifers is less than 3 l/s and is related to the periodicity of wet and dry periods.
More than one third of Spanish territory contains groundwater aquifers. Groundwater in porous media covers an area of 79,258 km2 (16% of the whole country), karst groundwater is spread over an area of 54,628 km2 (11% of the whole country) and other groundwater resources can be found in an area of 38,644 km2 (8% of the whole country).
The main aquifers are found in glacifluvial sand and gravel deposits. They cover only a few areas of Swedish territory, although more than three-quarters of the Swedish population is supplied with drinking water from these resources. Till, another porous aquifer, covers 75% of the country. Occasionally good yields can be achieved from these deposits, but wells in this area are mainly for single household supply. Aquifers in porous sedimentary rock are found in southernmost Sweden. They are very small regions compared to the total area of Sweden. Karst groundwater is rare in Sweden. Aquifers in the Archaean bedrock area have the largest areal extent of all aquifers. They can be found all over the country. Wells drilled in these rock types seldom yield more than 1 l/s, and are mainly for private water supply for single households.
The three most important aquifers are the Chalk, the Sherwood Sandstone and the Jurassic Limestones, which are consolidated, indurate sedimentary formations with dual porosity. The smaller aquifers have similar characteristics. They are formations in which groundwater flow has varying combinations of matrix and fractured flow components producing complex aquifers. These characteristics make representative sampling difficult. Another aspect is that smaller, but important, groundwater bodies are situated in consolidated sedimentary aquifers, which are often heavily exploited.