Hydro chemical Facies and Ionic Ratios of the Coastal Groundwater Aquifer of Saudi Gulf of Aqaba: Implication for Seawater Intrusion

It is now fairly documented that major ion chemistry of the groundwater can be used to determine an interaction between the groundwater and saline water in the costal aquifers, and that there exists a relationship between total dissolved solids and Cl-, Na+, Mg2+, and SO42- concentrations of groundwater. This hypothesis is tested on an aquifer located along the Saudi Gulf of Aqaba coast (Red Sea). Groundwater samples collected from 23 locations show the abundance of ions in the order of: Ca2+ > Na+ > Mg2+ > K+ = Cl- > SO42- >HCO3- > NO3-. The Piper trilinear diagram reveals two dominant clusters, i.e. the Ca2+-Cl--SO42- facies and the Na+-Cl--SO42- facies. Besides the major chemical compositions, ionic ratios (HCO3-/Cl-, Na+/Ca2+, Na+/Cl-, Ca2+/Cl-, Mg2+/Cl-, K+/Cl-, SO42-/Cl-, Ca2+/Mg2+, Ca2+/SO42-, and Ca2+/HCO3-) are used to evaluate the effects of saline water intrusions. Factor analysis of the studied samples demonstrates that changes in the groundwater composition are primarily controlled by mineral dissolution, human activities, weathering of marine sediments, evaporation/salinization of groundwater, and the residence time of water. An attempt has been made to identify hydrochemical processes accompanied with the current intrusion of seawater through the use of ionic exchanges. Following this procedure, about 7.97% mixing rate of seawater intrusion has been estimated for the month of March 2012. Furthermore, the seawater mixing index has also been applied, which resulted in a range of values from 0.395 to 7.922. These results determine 13 of 23 groundwater samples (57%) as saline, with electrical conductivity > 3000 mu S/cm.