GWB delineation in Finland Janne Juvonen Finnish Environment Institute WG C Meeting 20.3.2012

Background of GWB delineation Groundwater bodies have been mapped in Finland since the 1970s to be able to delineate important and potential groundwater bodies for water abstraction. A larger project to map and classify Finnish groundwater aquifers was carried out during 1988-1996 The aim was to increase information on the location of aquifers, hydrogeology, suitability for water supply, quality of groundwater, possible risk activities and contaminated sites (industry, roads, depositories, farming, gravel extraction sites etc.) The inventory was based on earlier studies, maps of subsoil and field work focused on checking the estimated boundaries and the soil material of the formations

GWB delineation The delineated area of the GWB is the area that affects the quality and quantity of the GWB. The outer boundary of the GWB has been drawn to reach soil with low permeability (for example 3 meters thick layer of clay or silt). Where this hasn’t been possible, the boundary has been drawn along a distinguishable map feature (for example a road etc.). During more detailed studies of the aquifer the delineation is usually rechecked and possibly redrawn. Margin belt

Groundwater area classification Total number of class I and II aquifers is 3800 Approximately 2200 aquifers are used for water abstraction (Class I) ~200 GWBs have no delineation  wells in bedrock or in an aquifer under a clay deposit

Horizons in Finnish GWBs There is no subdivision into several horizons in Finland because there is no relevant use of groundwater in deeper aquifers. In bedrock, groundwater is usually found in linear fracture zones but is very seldom used for water abstraction. The latest glaciation period wiped out many of the previous deposits so the aquifers occur mainly in superficial deposits such as eskers and ice marginal formations. In general there is little knowledge of other horizons and no systematic structural mapping of GWBs has been done in order to delineate other horizons. For example the Geological Survey of Finland has been involved in approximately 100 structural mapping of aquifers from the beginning of 90’s.

The size of GWBs All groundwater bodies are under 100 km2 , mean size is 2,7 km2 The estimated average yield in a typical small groundwater area is from 100 to 500 m³/d. The larger areas can have a yield up to thousands of m³/d. The feedback of GWB spatial datasets suggested that it would be possible to consider to eliminate GWBs of low relevance and small size – this option has not yet been discussed Also it was stated that delineation is not coordinated with Sweden (different GWB sizes) – were we supposed to?

SE FI

Corrections to spatial datasets GWBs overlapping with ERM boundary – will be corrected for next reporting of GWBs Subdivision to several horizons is very unlikely in the near future Number of attributes and shape files will be checked, but mostly the difference in numbers is caused by the 200 wells with no delineation Probably not possible by the end of March Optional attributes will be amended to some extent for the next reporting of GWBs Elimination of small GWBs – tempting, but where do we draw the line? Possible multipolygons

Thank You!