Study of the hydrogeochemical processes and its impact on the quality of groundwater in the area between Abu Simbil and Tushka, Western Desert, Egypt

The study area is located in a hyper arid area in the Western Egyptian Desert, which represents a massive agricultural project where irrigation water is extracted from the Nubian sandstone aquifer. This study focuses on the hydrogeochemical processes and its impact on the quality of the groundwater aquifer. Based on the geomorphology, the study area includes five geomorphological units, Wadi Kurkur bediplain, Aswan High Dam Lake, the Nile Valley, the West Dungul plain, and basement outcrops. According to the geology, the study area is distinguished by sedimentary cover ranging in age from Upper Jurassic to Quaternary. Regarding the hydrogeology of the study area, the Nubian sandstone aquifer is the main aquifer in the study area, which it is represented by 24 groundwater samples plus one sample from the stem of the Lake Nasser. All samples were collected, analyzed, and interpreted. Groundwater salinity classification shows that all the groundwater samples are fresh water types, except one sample considered brackish water type. The pH values of the selected groundwater samples vary from 5.8 in the center to 7.6 in the northern side, with a median value of 7.3. The relationship between salinity content and the other ions shows a strong correlation between the values of Ca²⁺, Cl^-, and SO₄^2- with the TDS values and a moderate correlation between Na⁺ values with TDS values. Silicate and carbonate weathering are the main hydrochemical processes affecting the groundwater. From the saturation indices (SI) results, it is indicated that gypsum, anhydrite and manganite dissolve with negative SI values, whereas iron minerals are supersaturated with positive values. The hypothetical salts indicate a recharge from the lake Nasser in addition to leaching and dissolution of terrestrial salts. From the mixing Model, it is indicated that the Nubian sandstone aquifer has paleowater contribution percent ranging from 81 to 92% and Lake Nasser water contribution percent ranging from 7 to 18%. The nitrate concentrations are below the maximum allowable limits of the WHO; however, high concentrations of heavy metals were recorded in the groundwater samples at various extents.