Hydrochemical and isotopic characteristics of thermal groundwater at Farafra Oasis, Western Desert, Egypt

Abstract

Groundwater from the Nubian sandstone aquifer at Farafra Oasis in the Western Desert of Egypt has been investigated using chemical tracers and environmental isotopes to clarify the hydrochemical features of this aquifer. The majority of the collected samples are characterized by Ca-Cl water type, which may be attributed to dissolution of the carbonate-rich sediments. Calculated saturation indices show that the main hydrogeochemical processes were the dissolution of carbonates and evaporites and the precipitation of Fe-rich minerals. Temperatures calculated using the K-Mg geothermometer show that the reservoir temperature ranges from 58°C to 121°C. The groundwater samples have δD and δ18O values similar to the isotopic content of the Nubian aquifer palaeowater in the Western Desert. Additionally, the isotopic composition suggests that there is no active potential current recharge from the local precipitation. Gamma spectrometry of 226Ra, 232Th and 40K activities indicates that the groundwater of the Nubian aquifer is safe with respect to radioactivity. Groundwater in Farafra Oasis is the main source of irrigation and drinking water for local residents. All the samples are excellent for irrigation uses for all types of crops. It is suggested that the water samples may require some treatment regarding the high iron content before usage as drinking water.Supplementary material: Locations of the collected groundwater samples and their Na-K-Mg ternary cation plot is available at https://doi.org/10.6084/m9.figshare.c.4938252