ABSTRACT
Much of the chemical character of groundwater is established within the soil and the unsaturated zone. This is a region where there are rapid changes in water chemistry. There are probably few hydrological systems that are not influenced by the activities of man. The presence of tritium derived from thermonuclear tests, trace levels of synthetic organic compounds and acidification in remote mountain areas are clear evidence of this. Geochemical inputs arise from the atmosphere, soil, vegetation and the bedrock and give rise to varying concentrations of different chemical elements and species. A number of natural processes can be identified by which groundwater gains its intrinsic properties. Most of the chemical properties of groundwater are attained rapidly, during movement through the soil and the unsaturated zone, and an understanding of the reactions that occur there are of particular importance in hydrogeochemical studies.
