Investigation of groundwater based on stable isotopes and major ion geochemistry in the Eocene carbonate aquifer, East Beni-Suef area, Eastern Desert, Egypt

Abstract

The East Beni-Suef region represents one of the most promising areas for agricultural development projects in Egypt. Groundwater from the Eocene Carbonate Aquifer is the main source of water for such projects all over the country. This aquifer covers about 50% of Egypt. It is shallower and easier to access with low drilling costs as compared to the Nubian Sandstone Deep Aquifer. This study aims to identify the origin and sources of recharge to this aquifer to better understand the sustainability and quality of the groundwater in this region. Stable isotopes and major ion geochemistry were used to achieve this goal. Groundwater samples and surface water from the Nile River were collected and analyzed for stable isotopes (δ18O and δD) as well as major ions such as Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, and SO42−. The results showed that groundwater samples varied in salinity from fresh to brackish (735 mg/L to 2680 mg/L). The major ion geochemistry revealed that the water type has evolved from Ca–Mg–HCO3 to Na–Cl–SO4. The suggested main processes that control the water chemistry in the study area are water-rock interactions involving evaporite dissolution and cation exchange. The results of δ18O and δD showed that the Eocene Carbonate Aquifer, in the study area, is mainly recharged from the Nile River and from the Nubian Sandstone Deep Aquifer at different ratios. The degree of contribution from these two end members was largely based on the location of wells from the Nile River, the water depth, and the structural setting. For the first time, depleted groundwater (δ18O = −10.16 ‰ and δD = −62.65 ‰) was recorded in the Eastern Desert, Egypt, in this research work. The assessment of groundwater quality for drinking and irrigation purposes is also provided in this study.