Hydrogeochemical characterization of groundwater aquifer in Al-Madinah Al-Munawarah City, Saudi Arabia

Abstract

In the Al Madinah Al Munawarah city, urbanization has accelerated rapidly over the last few decades which has caused both decline of groundwater level and deterioration of groundwater. The city is located in the center of sedimentary basin that consists of alluvial deposits originated from the erosion of surrounding igneous rocks. It has been grown very rapidly both in population and land use. The hydrogeological and hydrogeochemical characteristics of Al Madinah Al Munawarah city have been studied. The only recharge source of the groundwater of the study area is rainwater. Concentrations of total dissolved solids, major constituents, and trace elements in groundwater increased significantly after construction of industrial area to the south of the city near Wadi Al Aqiq and after increasing the urbanization, indicating an important pollutant process over the study area. The EC and TDS values ranged widely from 1,179.83 to 9,843.03 μmohs/cm and from 755.09 to 6,299.54 mg/l, respectively. Such a wide range of EC and TDS values indicate that the hydrochemistry of groundwater is controlled by various hydrochemical processes such as agricultural and farm activities, industrial development, landfills leachate, septic tanks, and wastewater of municipal and domestic consumption. Hydrochemical facies of groundwaters change broadly from a Ca-SO4 type in southwestern part near Wadi Al Aqiq to a Na-Cl type in both southeastern part at Harrat Rahat and northern part of the study area. Values of Na/Cl ratio indicate that silicate weathering and halite dissolution are the main processes resulting in release of Na into groundwater. Nitrate originates from fertilizers application and leakage of sewage with the highest value of 261 mg/l. Groundwater samples from southeastern part have high levels of heavy metals which render them unsafe for drinking purposes as compared with WHO guidelines. Where the maximum concentration values reach 0.850 mg/l for Fe, 0.120 mg/l for As, 0.985 mg/l for Ba, 1.030 mg/l for V, and 0.890 mg/l for Al. These high concentrations are mainly derived from leakage from the unlined industrial wastewater disposal site located to the southwest of the city. Disposal of industrial wastewater in such insecure landfill should be prohibited and the landfill should be properly designed to prevent further groundwater pollution.