Modeling of limestone aquifer in the western part of the River Nile between Beni Suef and El Minia

Abstract

A robust classification scheme for partitioning groundwater chemistry into homogeneous groups was an important tool for the characterization of Eocene limestone aquifer. The aquifer locally is composed of chalky limestone with thin clay intercalated (Samalut Fm.), the fissures, the joints, and the fractures are represented the conduits of the aquifer system. The flow patterns are conditioned by karstification processes which develop a conduit network and preserve low permeability microfractured blocks. The aquifer is mainly recharged by surrounding aquifers and agricultural wastewaters. The groundwater flows in the eastern part (due the Bahr Yossef and River Nile), which is a discharge area rather than a recharge. Twenty-eight groundwater samples was collected from the Eocene limestone aquifer and analyzed for isotopes, major, and trace elements. δD and δ18O concentrations ranged widely due to geology, infiltration of different surface waters, evaporation, and hydrogeology. The concentration of δD and δ18O isotopes is depleted in the northern zone of the northern part and western zone of the central and southern part of the study area. They are enriched due the eastern area of the central and southern part of the study area. δD vs. δ18O delineate the Pleistocene aquifer and has a strong influence than other waters on aquifer hydrogeochemistry. It is confirmed by the AquaChem outputs of the mixing proportions of different water types included in the aquifer system. Cl-δD and Cl-δ18O relationships indicate the role of evaporation especially due the eastern area of the central and southern part of the study area. This research tests the performance of the many available graphical and statistical methodologies used to classify water samples. R-mode clustering, correlation analysis, and principal component analysis were investigated. All the methods were discussed and compared as to their ability to cluster, ease of use, and ease of interpretation. Nearly most low-salinity waters are in equilibrium to supersaturate with respect to both carbonate minerals, while it is shifted to undersaturate with salinity. The inverse modeling findings clarify that the calcite, gypsum, and anhydrite dissolution increased due the northeastern area, middle zone, and southern corner of the northern, central, and southern part of the study area, respectively. The latter areas also were characterized by the lowest precipitation of the dolomite. Such areas are distinguished by much more enhancement for aquifer permeability and therefore transmissivity. The latter areas can be use as injection zone by fresh water. It can be a triple function; firstly, it recharges the saline Eocene limestone aquifer through the enhancement hydraulic conductivity and dilutes it. Secondly, it enhances much more the aquifer permeability and therefore the transmissivity. The Eocene limestone aquifer can be improved in quality and quantity by using such a model and exploits it as an alternative water resource with Quaternary aquifer and Nile water. Thirdly, it irrigates more areas to increase the income/capita. The dedolomitization represents the main hydrogeochemical process in the aquifer system. The geomedia (limestone, clay, marl, shale, and sand deposits) are in contact with water, therefore, the rock/water interaction, mixing, and ion exchange were estimated by the geochemical evolution of the groundwater systems.