Long-term changes in groundwater chemistry in four coastal water supply plants in southern Finland

Monitoring of four glacial outwash aquifers that have been utilised during the last 30 years for municipal water supply of Espoo community, southern Finland, reveals changes in chemical composition of groundwater. A 1.5 to 2.0-fold increase in electrical conductivity and in concentrations of main cations and anions in abstracted groundwater reflect primarily the geological impact of Litorina deposits. Relict seawater trapped in deeper parts of aquifers and leaching of fossil salts from postglacial clay and silt deposits have a marked effect on the chemistry of groundwater.