Date of Award
Doctor of Philosophy
Dr. Alan E. Kehew
Dr. Mohamed Sultan
Dr. R.V. Krishnamurthy
Dr. Laura J. Crossey
The Nubian Sandstone Aquifer System (NSAS) of northeastern Africa is one of the largest confined fossil-water aquifer systems in the world, with several nations relying on it (Egypt, Libya, Sudan and Chad). This groundwater is the biggest and in some cases the only future source of water to meet the development goals of each NSAS country. This study provides new geochemical data from the main oases of the Western Desert of Egypt and a compilation of published hydrochemical data from the regional aquifer. Interpretation of results suggests heterogeneous fluid mixing within the aquifer, the potential for hydrochemical sub-basins, and a connection between water quality, water management, and tectonics. Results of this study will help in the development and sustainable management of the continental-scale NSAS.
The water samples were collected from deep wells in the main oases of the Western Desert of Egypt, including from north to south: Bahariya, Farafra, Dahkla, and Kharga. Results show highly variable temperatures (20oC to 56oC) that partly reflect depth of sampling but also suggest a possible additional heat source arguably due to deep fluid mixing. Stable isotopes of oxygen and hydrogen provide some evidence for this mixing, taking place to varying degrees within Nubian aquifer waters. Salinity and pH values are low. High iron content impairs water quality.
A strong evidence for deep fluid inputs into the NSAS is from 3He/4He ratios based on values that range from cratonic values of 0.02R^ up to values of 0.35 (4% mantle helium) in Egypt and 1.45R^ (18% mantle helium) in Libya. This suggests that, in both locations, deeply sourced fluids, including mantle-derived fluids, are likely leaking into the NSAS along fault systems below the aquifer.
Hydrochemistry data marked by a high content of CO2 in the Nubian aquifer waters also seem to indicate a deep source. Analysis of carbon isotope suggests average aquifer values have about 34% of the carbon from deep sources, 22% from dissolution of limestone, and 44% carbon from organic sources with the variability in these values also suggesting fluid mixing but not necessarily at the percentage level implied.
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Mohammed, Abdel Mawgoud, "Deep Fluid Inputs into the Continental-Scale Nubian Sandstone Aquifer System Constrained by Hydrochemical, Stable Isotope, and Noble Gas Data" (2015). Dissertations. 1192.