Mapping and classification of Finnish groundwater areas

To improve the protection of Finnish groundwater resources, a project on mapping and classifying groundwater areas was initiated in the 1980s. The purpose of this exercise was to identify priority areas for groundwater utilization and to improve the management of groundwater. The mapping and classification project was carried out from 1988 to 1995.

Groundwater area

Classification

The classification divides groundwater areas into three classes according to their priority:

• Class I: groundwater area important for water supply           
• Class II: groundwater area suitable for water supply
• Class III: other groundwater area
  

An important groundwater area is an aquifer from which 10 or more dwellings obtain their water. A groundwater area suitable for water supply refers to an aquifer which could be acceptable for water supply but which, for the time being, is not currently needed by a community or a sparsely populated region, or for any other water supply purposes. For Class III groundwater areas, evaluating their degree of usability requires further study of their feasibility for water supply, of their water quality and potential sources of contamination or of other alterations. Therefore, the classification of these groundwater areas may change after the studies are completed. By the end of 2007, almost 6350 groundwater areas had been defined. Of these, approximately 2250 belong to Class I,(area about 6200 km² ), 1500 to Class II (area 3500 km²) and 2600 to Class III (area 3600 km ²).

Hydrogeology of Finnish glacial deposits

The whole of Finland has been shaped by glaciation, and although the variety of glacial landforms is great, only a few are considered suitable for use as groundwater areas. These are the landforms of glacial sediments, formed both through glacial and glaciofluvial deposition.

Eskers

Eskers are glaciofluvial in origin and are associated with subglacial and englacial melt water channels. They appear as gently winding chains of sediments and are often parallel to the direction of ice flow. In Finland four main types of esker are found: steep-sided esker, flat-topped esker, deep-rooted esker and till-covered esker. Because of the glaciofluvial origin, the sediments have been sorted and usually consist of sandy material, but in the core of the esker, cobble- and boulder-predominant material may occur.

Moraines

This is quite an open term referring to a variety of landform types formed through the glacial deposition of unsorted till. The type of moraine is defined by its mode of deposition rather than by any physical features it may possess. Although moraines make up the vast bulk of glacial deposits in Finland, most are too small for use as municipal groundwater supplies. In many cases, however, moraines may make up part of a larger glacial formation which is used for groundwater supply. Moraines may also be used as aquifers when they have acted as traps for sand banks in an ancient marine environment; here, a large quantity of sand is deposited around a moraine core.

Ice margins

The Salpausselkä ice margins and the Central Finland ice margin formation are composed of a mixture of deltas, moraines and the ends of esker chains, and mark the southern edge of the Baltic ice lobe at various times (Salpausselkä I, II and III). The ice margins are combinations of eskers, deltas and end moraines in which sorted sediments predominate. The deltas are often associated with the esker chains and represent the final stage of esker formation when the subglacial and englacial channels reached the margin of the ice sheet. The hydrology of the ice margins is complex due to the variety of smaller formations contained within the whole; however, the typical sediments making up an ice margin are sands and gravels and thus ideal for the storage of groundwater.