Geochemical modeling of the hydrogeochemical processes affecting groundwater quality of the Eocene aquifer east of El Minia Governorate -Eastern desert - Egypt

摘要

The Eocene limestone aquifer represents a renewable source of groundwater that can be used to enhance the sustainable agriculture at the eastern desert fringes of El Minia Governorate. The current research aims to investigate quantitatively the physicochemical processes which control the chemical composition of groundwater extracted from the Eocene aquifer using the PHREEQC code. The total dissolved solids of the Eocene groundwater range from 453 to 1903 mg/1 indicating fresh to slightly brackish water quality. The simulation of the double mixing between rain (or Nile) water with Nubian water reveal that rain or Nile water contribution by 50% or more to the Eocene limestone aquifer system can explain the chemical composition of most groundwater samples of the Eocene aquifer. This means that the contribution from rain or Nile water infiltration to the Eocene aquifer is much more important than upward leakage from the underlying Nubian sandstone aquifer. The triple mixing processes simulation indicate also that the most effective end members of mixing are found to be rain and Nile waters, with some contribution from the groundwater encountered at the Nubian sandstone aquifer. The evaporation of 75%-95% of rain or Nile water explain the chemical content of most water samples which imply that evaporation is a dominant physicochemical process at East of El Minia area due to the elevated air temperature and the exploitation of groundwater at relatively shallow depths. The results of the current geochemical modeling study indicates that there are processes other than evaporation and mixing which affect the groundwater quality of the Eocene aquifer (such as carbonate and sulfate minerals dissolution). Finally, the usage of PHREEQC code in the quantitative assessment of the Eocene aquifer can be applied for similar aquifers and areas surrounding the Nile Valley Region in Egypt. This region comprises six governorates (Beni Suef, El Minia, Assiut, Sohag Qena and Aswan) where 40% of the population of Egypt live.