One akvifer is a geological formation that stores groundwater with such a large storage capacity and such a large permeability that groundwater can be extracted from it in useful quantities. An aquifer may have one or more groundwater reservoirs.
According to the definition in the Water Framework Directive, an aquifer is "one or more layers below the surface, of bedrock or other geological layers, with sufficient porosity and permeability to allow either a significant flow of groundwater or abstraction of significant amounts of groundwater".
The word aquifer comes from Latin and means roughly water carrier.
Different types of aquifers
If the groundwater is separated from the atmosphere by an aquifug or an aquiklud, we are talking about a closed aquifer. For example, solid granite does not let water through at all and forms an aquifug, while moraine clay, which only lets through very little water, forms an aquiklud. A closed aquifer can thus consist of a sufficiently large amount of groundwater which is stored in a layer of gravelly sand which in turn is placed under a thick, for water largely impermeable, layer of moraine clay. When the groundwater level rises so high that it abuts the aquifuge, it is said that the groundwater has reached it potentimetric groundwater surface (previously the term was also used piezometric groundwater surface). The water in a closed aquifer is normally under a greater pressure than the water in an open aquifer.
One open aquifer is an aquifer that does not lie under an aquifug or aquiklud. For example, groundwater stored a bit down in sandy gravel. In the relatively unusual cases where the groundwater surface rises above the ground surface, one speaks of an artesian aquifer. Common to open and artesian aquifers is that the groundwater level in them is affected by the air pressure. A higher air pressure gives a lower groundwater level.
Internationally (and also on many Swedish hydrogeological maps) aquifers are divided into the following groups; porakviferer, crack aquifers and karst. Pore aquifers consist of groundwater stored in various forms of soil types, coarse-grained sandstone and porous limestone. Crack aquifers consist of groundwater stored in cracks and crushing zones in crystalline rocks (eg granite and gneiss). Karst is a form of system of further cracks, layer joints and cave systems, for example in limestone where groundwater is stored.
In Sweden, an aquifer is called small aquifer if a quantity of water less than five liters per second can be extracted.
Read the article on wikipedia
An example of where to use aquifers is Arlanda Airport
With the aquifer reduces the airport's annual electricity consumption by 4 GWh and the district heating consumption by around 15 GWh, ie a total of 19 GWh, which corresponds to the annual use of energy for 2000 villas or the entire annual use at Malmö Airport. 7,000 tonnes of carbon dioxide per year do not need to be released.
Read more about Arlanda Airport aquifer