Scientific African (Jul 2023)
Hydrogeological and hydrogeochemical insights on the salinization of the shallow groundwater aquifer in Siwa Oasis – Western Desert – Egypt
Abstract
Siwa Oasis is one of the most important Oases in the Western Desert. Groundwater is the only water source. Nubian Sandstone Aquifer is the main supplier of fresh water. Carbonate aquifer is represented by two zones, shallow fracture limestone aquifer and deep fracture chalky limestone aquifer. The productivity of this aquifer is varied from place to another due to the variation of the fracture density and the degree of connection with the recharge sources. 106 groundwater samples were collected and analyzed from the shallow aquifer to investigate the phenomenon of salinity rise. Groundwater salinity classification shows that the majority (79%) of the private groundwater wells is brackish groundwater and the rest (21%) are fresh groundwater. On the other hand, the majority (80%) of the governmental groundwater wells is brackish, and the rest (20%) are saline groundwater type. The relationship between salinity content and the other ions indicates that calcium, chloride, magnesium, and sodium are the effective ions which caused an increase in salinity content in case of private groundwater, while calcium, chloride, sulfate and sodium are the effective ions in case of governmental groundwater wells. Dissolution and ion exchange are the main hydrochemical processes affecting the groundwater. From the hypothetical salts it is indicated that the shallow groundwater aquifer in the study area is highly evolved as it's enriched with marine residual indicated by the presence of NaCl, MgCl2, MgSO4, CaSO4, Ca(HCO3)2 salts. Principal Components Analysis (PCA) indicated that there are two principal components extracted have eigenvalues greater than 1 in case of the private groundwater samples and one principal component for the governmental groundwater samples. All these components are defined as the leaching and dissolution of marine and terrestrial salts which due to salinization of the carbonate aquifer in the study area.
