Geochemical Investigations

Abstract

Saltwater intrusion is one of the most widespread and important processes that degrades water-quality by raising salinity to levels exceeding acceptable drinking and irrigation water standards, and endangers future exploitation of coastal aquifers. This problem is intensified due to population growth, and the fact that about 70% of the world population occupies coastal plains. Human activities (e.g., water exploitation, including industry and agriculture, reuse of waste water) result in accelerating water development and salinization. The elucidation of the dynamic nature of the fresh-saline water transition zone is of both scientific and practical interest because it reflects or controls the extent of development or exploitation. The source of salinity in coastal aquifers has been a subject of many studies, but in many cases is still equivocal. Seawater encroachment inland is the most commonly observed reason for the increase in salinity, but other sources or processes can cause an increase. Custodio [1997J listed several saline sources that can affect water quality in coastal aquifers, but which are not directly related to seawater encroachment. These include entrapped fossil seawater in unflushed parts of the aquifer following invasion of seawater during relatively high sea levels, sea-spray accumulation, evaporite rock dissolution , displacement of old saline groundwater from underlying or adjacent aquifers or aquitards through natural advection or thermal convection, leaking aquitards through fault systems, and pollution 51