Factors Governing Groundwater Chemistry in Paleozoic Sedimentary Aquifers in an Arid Environment: A Case Study from Hail Province in Saudi Arabia

Abstract

The present study focuses on evaluating the groundwater quality in parts of the Hail Province of Saudi Arabia. Hail province is the home to the Hail Agricultural Development Company and is dependent entirely on the groundwater resources available from the Saq aquifer for agricultural productivity. Twenty-four groundwater samples from agricultural farms were analyzed for their major ion concentrations. The TDS content of the collected samples ranged from 245.9 to 869.20 mg/l, whereas the EC values were below the maximum permissible limit of 1,400μS/cm prescribed by WHO for drinking water. The cation and anion concentrations were in the following order: ${{\rm Na}^{+} > {\rm Ca}^{2+} > {\rm Mg}_{2}^{+} > {\rm K}^{+}\,{\rm and}\,{\rm HCO}_{3}^{2-} > {\rm Cl}^{-} > {\rm SO}_{4}^{2-} > {\rm NO}_{3}^{2-}}$. The major groundwater facies identified included the Ca(Mg)–Na(K)–Cl–${{\rm SO}_{4}-{\rm HCO}_{3}}$ type, Ca(Mg)–Na(K)–${{\rm HCO}_{3}-{\rm Cl}-{\rm SO}_{4}}$ type and the Na(K)–Ca(Mg)–Cl–${{\rm SO}_{4}-{\rm HCO}_{3}}$ type. The samples fall in the rock–water interaction zone on the Gibb’s plot. Carbonate weathering, silicate weathering and reverse ion exchange are the major chemical processes which govern the chemistry of the groundwater in the area. The sodium adsorption ratio values for all the samples are below 10 and are excellent for irrigation. In terms of residual sodium carbonate, the values are <1.25 and are considered good for irrigation.