Saltwater intrusion in drinking water wells of Kordkuy, Iran: an integrated quantitative and graphical study

Seawater or saline water intrusion into coastal aquifers is one of the most challenging and widespread environmental problems that threaten the groundwater quality and sustainability. Extensive groundwater extraction in Kordkoy aquifer, mainly for municipality and agricultural development, has caused substantial seawater encroachment and upcoming of the deep saline water into the aquifer. This study was conducted to assess saline water intrusion into drinking water wells using hydrogeochemical approaches (quantitative and graphical). For this purpose, 28 water samples were collected from drinking water wells over two seasons to analyze 16 water quality parameters. The results of five chemical indicators encompass chloride concentration, Na/Cl, Ca/Mg, and Cl/(HCO 3 + CO 3 ) ratios, and BEX indices revealed that more than 60% of drinking water wells in the study area were influenced by seawater or saline water. Furthermore, reverse ion exchange and salinization are the dominant ionic processes in the aquifer. The chemical indicator results, on the whole, were supported by various graphical techniques such as the bivariate plots of Cl versus EC, TDS versus Na/(Na + Cl), total dissolved ions (TDI) versus other major ions together with Stiff, Piper, Durov, HFD, and Gibbs diagrams. Results showed that except one well, which was harmfully contaminated by saline water, the sampling water wells, on the whole, were divided into three homogeneous chemical classes; unaffected, slightly, and moderately influenced by saline water. Since the preliminary results of geophysical surveys in the study area revealed a layer having an electrical resistivity of less than 5–10 Ωm in an average depth of 120 m, there is a quite high possibility of saline water intrusion from the subsurface layers due to high depth and discharge rate of some drinking wells.