Evaporation, fractional crystallization, and reverse ion exchange variables governing the chemistry of the groundwater in Al-Wajh Region, Saudi Arabia

Groundwater is a valuable water resource in Saudi Arabia due to the scarcity of sustainable/renewable water sources. Therefore, the systematic and continuous monitoring of groundwater is essential to ensure its effective and sustainable management. This aligns closely with the objectives of the Kingdom’s National Water Strategy, which emphasizes the preservation, efficient utilization, and long-term sustainability of groundwater resources to support national development and water security. This study represents a hydrochemical assessment for groundwater sources in ten sites within Al-Wajh municipality, western region of Saudi Arabia. The results indicate that the concentrations of all dissolved ions in the analysed samples exceeded the permissible limits set by the World Health Organisation (2011). Apparently, this groundwater is extremely mineralized and is not appropriate for drinking use without proper treatment. The relative abundance of main ions follows the order: Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ > Cl⁻ > SO₄²⁻ > HCO₃⁻ > NO₃⁻. This delivery confirms that the strong acidic ions such as sulfate (SO₄²⁻) and chloride (Cl⁻) are predominate over weak acid anions like bicarbonate (HCO₃⁻) and carbonate (CO₃²⁻). Piper diagram shows that groundwater form mixed facies of CaMgCl, CaCl, and NaCl. The correlation between total dissolved solids (TDS) and the ratios of Cl-/(Cl-+HCO3-) or Na+/(Na++ Ca2+ ) confirms that evaporation and fractional crystallisation are the key variables influencing chemistry of the groundwater in the investigated area. The results of this investigation provide a preliminary evidence that Na+, Ca2+, and Mg2+ participate in the reverse ion exchange mechanism. Sodium adsorption ratio (SAR) and electrical conductivity (EC) calculations indicate that about 60% of the groundwater samples are inadequate for irrigation purposes. Meanwhile, the Wilcox diagram reveals that 10% of samples classified as disputable, while 90% have high EC values, which render them inappropriate for the irrigation of many crops.