Atmospheric, Geological, Marine and Anthropogenic Effects on Groundwater Quality in Finland

The atmospheric, geological, marine and anthropogenic factors affecting the chemical quality of groundwater are evaluated. Sulphates and nitrates derive mainly from the atmosphere as wet or dry deposition in weakly mineralized shallow groundwater in natural uncontaminated surficial aquifers. The texture, structure and lithologic composition of aquifer material have an impact on water chemistry although marine influence and anthropogenic pollution generally outweigh the geological influence. Relict seawater trapped in deeper parts of confined aquifers and in bedrock covered by clay deposits has a marked effect on the quality of groundwater drawn from wells drilled into bedrock in the broad coastal belt. Brackish or saline groundwater is encountered all over the country in holes drilled in crystalline bedrock to a depth of more than 500 to 1000 metres. The lithologic environment affects the quality of deep bedrock groundwater which tends to change from Na-Cl type towards Ca-Na-Cl type with increasing salinity and depth of occurrence. Anthropogenic pollution is reflected in elevated amounts of all major dissolved components, although the most sensitive indicators of contamination are nitrates, chlorides and potassium. Nation-wide hydrogeochemical mapping of rural water sources revealed that shallow wells dug into glacial till deposits had the highest median NO₃ contents, and that spring water discharging from glaciofluvial sand deposits had the lowest. The quality of groundwater distributed by public waterworks is generally good.