Hydrogeochemical tracers to assess the groundwater in El Saieda Basin, western desert, Aswan, Egypt

Abstract

Egypt is a country that heavily relies on agricultural activities. River Nile serves as the primary source of irrigation water for agricultural purposes. El Saieda Basin project, located in the southern western desert of Egypt, represents a massive agricultural project where irrigation water is distributed from the River Nile through an extensive network of canals. This study focuses on evaluating the groundwater resources, the groundwater quality, and the hydrochemical processes affecting the groundwater within El Saieda Basin to provide an additional source of irrigation water and to ensure a safe water supply for the residential villages. Various data sets were integrated, including geomorphology, geology, hydrogeology, hydrogeochemistry and stable isotopes. Based on the geomorphology; the study area includes four geomorphological units, Structural Plateau, Bajada Plain, Eroded old Nubian surface, and Nile alluvial Plain. According to the geology; the study area is located in the southern part of the Western Desert. The dominating geological units in this part of Egypt range in age from Lower Cretaceous to Recent. Regarding the hydrogeology of the study area; the Quaternary aquifer is the main aquifer in the study area where 24 groundwater samples plus two surface water samples (irrigation canal + main Drain) were collected and analyzed. Groundwater salinity classification shows that 17% of the total groundwater samples are fresh groundwater samples with values that range between 550 and 996 mg/l with an average of 775 mg/l. 29% of the total groundwater samples are brackish groundwater samples with values that range between 1177 and 2273 mg/l with an average of 1868 mg/l. In addition, 46% of the total groundwater samples are salty groundwater samples with values that range between 3197 and 4886 mg/l with an average of 4037 mg/l. The rest of the groundwater samples (8%) are saline groundwater samples with a maximum value of 9018 mg/l and an average of 7645 mg/l. The groundwater's temperature ranges from 25 to 30.9 C. However, the measured pH values showed relatively neutral water where the values range from 6.6 to 7.6. The relationship between salinity content and the other ions indicates that sodium, calcium, magnesium, sulfate, and chloride are the effective ions that increase the salinity content. Silicate weathering and dissolution of calcite are the main hydrochemical processes affecting the groundwater. From the saturation indices (SI) results it is indicated that Gypsum and Anhydrite dissolve with negative SI values, whereas iron minerals are supersaturated with positive values. Carbonate minerals are insufficiently soluble in groundwater, with values that fluctuate positively and negatively around zero. From the hypothetical salts, it is indicated that the quaternary groundwater aquifer in the study area is highly evolved as it's enriched with terrestrial and marine residuals indicated by the presence of NaCl, MgCl2, MgSO4, CaSO4, Ca(HCO3)2 salts. From the Environmental Stable Isotopes, it is indicated that all the groundwater samples are enriched by 18O and Deuterium which indicates a recharge from the main irrigation canal and return flow irrigation water. Trace elements results indicated that the groundwater is suitable for human drinking according to the World Health Organization and also for irrigation according to the Australian guidelines for irrigation water quality.