Evaluation of seawater intrusion of Urmia Lake into the Ghalghache coastal aquifer

The uncontrolled groundwater extraction, low precipitation and falling water table depth cause a modification of natural flow systems and induce seawater intrusion from the coast finally resulting in the groundwater quality deterioration. The principal aim of this study is to determine the extent of seawater intrusion in the aquifer, characterize the hydrochemistry of the Ghalghachi aquifer, and identifying the main processes that occur in the system. In order to achieve this aim, chemical parameters of the area during May and September 2006 were measured, such as electrical conductivity, pH, anions and cations concentrations. In this study, the seawater intrusion or salinization in a coastal aquifer was evaluated using groundwater chemistry data, ionic ratios and calculation of indices. A large proportion of the groundwater is classified as Na-Cl, Ca-HCO3 and Ca-Cl types. The Na-Cl types represent effects of seawater intrusion. Major ionic compositions effectively indicated effects of the seawater intrusion and especially Cl and EC are the simplest indicators for the salinization process. The Cl concentrations and EC levels are highly positively associated. Lower ratios of Na/Cl and SO4/Cl than the seawater ratios indicated the seawater encroachment. The analytical results obtained in the hydrochemistry study were interpreted using ion correlations with chloride, and calculations of the saturation indices (SI) and ionic deviations (Δ). The results of calculation of the saturation indexes (SI) and ionic deviations for cation of coastal groundwater showed that the saturation index for carbonate minerals is positive and for sulfate minerals is negative. The ΔNa+ is usually negative and the ΔCa2+ and ΔMg2+ are positive and samples plot below the mixture line and seawater intrusion in the aquifer. The most remarkable process was found to be the inverse cation exchange.