Geochemical and Isotopic Constraints on the Recharge and Salinization Origin of Groundwater Aquifers in El Rina–Nihayaat, South Sinai, Egypt

The Sinai Peninsula is located in the arid regions of Egypt where groundwater is the sole source for drinking and irrigation and future development. Regular assessment of the geochemical processes governing the groundwater quality is important in arid regions and paleo-aquifers. This research focuses on investigating the groundwater sustainability of the Upper Cretaceous Aquifer (UCA) located at El Rina–Nihayaat area, Southwestern Sinai Peninsula. The study aims to evaluate the main source of groundwater recharge and investigate factors deteriorating groundwater quality. The study is based on the geochemical and isotopic analyses of 31 groundwater samples tapping the UCA. The groundwater flows toward the Gulf of Suez. The groundwater salinity ranges from 1078 mg/L to 13090 mg/L indicating brackish to saline water. Two main water types have been delineated: Cl-Na and Cl-Ca indicating the final stage of groundwater evolution and leaching and dissolution of aquifer matrix of marine origin. The spatial distribution of the groundwater salinity and major ions (Na+, K+, Ca2+, Mg2+, SO42-, and Cl-) increase toward the Gulf which coincides with the direction of the groundwater flow, while bicarbonate increases toward the upstream watershed. Most of the groundwater samples tapping the UCA are depleted with the isotopic content of the stable isotopes where they range from -4.43 ‰ to -6.37 ‰ for δ18O and -28.3 ‰ to -40.2 ‰ for δ2H. The groundwater samples are depleted relative to the recent rainwater and enriched to the Nubian Sandstone located underneath the UCA indicating mixing from both source(s). The mixing estimated percentages from the recent rainwater using calibrated geochemical NETPATH model range between 48.6% to 88.5% while the upward Leakes from the Nubian water ranges between the recent rain and the paleo-Nubian water ranges between 48.6 % and 88.5 % from the meteoric rainwater, while the upwelling recharge from the paleo-Nubian groundwater ranges between 11.5 % to 51.4 %. The factorial analyses indicate three main factors governing the geochemistry of groundwater in the UCA: including water-rock interactions, meteoric recharge from annual precipitation, and upward leakages from the underneath paleowater.  Further exploration for the UCA is recommended to determine the promising zones receiving a considerable amount of the recent rainfall.