GEOCHEMICAL AND HYDROLOGICAL PROCESSES CONTROLLING GROUNDWATER QUALITY IN ASSIUT GOVERNORATE, EGYPT: GEOCHEMICAL AND ISOTOPIC EVIDENCE

Groundwater in Assiut area, Egypt, is an important source of fresh water for human consumption, agriculture, and domestic and industrial purposes. Due to a growing population, there is an increasing water demand in this arid region. This study has investigated the geochemical and hydrological processes that control groundwater quality within the Pleistocene, Plio-Pleistocene, and Eocene aquifers in Assiut. A total of 28 surface and 160 groundwater samples were collected for geochemical analysis (major and minor element chemistry, and stable isotope analyses). Total dissolved solids = 182 to 5657 mg/L, water-d¹⁸O = -7.5 to +6.5‰, and water-dD = -55 to +32‰.

Results indicate that evaporation prior to infiltration, mixing, and mineral equilibria (dissolution and precipitation) are the main factors that affect water quality. Ion exchange plays a secondary role in controlling the water chemistry of the Pleistocene aquifer, but is more effective in controlling water quality within the Plio-Pleistocene and Eocene aquifers. Geochemical and stable isotope data indicates that the principal source of recharge to the Pleistocene and Plio-Pleistocene aquifers is the surface water system (irrigation canals), while the prevalence of Na-Cl type waters in the Eocene aquifer indicates recharge by upward leakage from the underlying Nubian sandstone aquifer which contains Na-Cl water.

The fresh water exploited from the Eocene aquifer may be of great importance for land reclamation projects not only at the western desert fringes, but also at the eastern desert fringes of Assiut and similar settings around the River Nile south of Assiut Governorate. Results of this study will be helpful for sustainable development, and raising the standard of living of people in the Assiut area, which is one of the poorest regions of Egypt. Future work will consider the quantification of these geochemical processes based on numerical simulations using appropriate geochemical modeling codes.

Corresponding author: Current address: Department of Geological Sciences/MS 172, University of Nevada, Reno, NV 89557, USA.