Effect of the Nile Aquifer Lithological Characteristics on Groundwater Chemistry in Assiut Governorate, Egypt

The chemical composition of groundwater is affected by many features, including the impact caused by surrounding rocks. The Nile aquifer is surrounded by the calcareous structural plateau along the Assiut governorate on both sides. This paper aims at studying the effect of surrounding rocks on the chemical composition of groundwater in the Nile aquifer along the Assiut governorate. Fifty-five samples were taken from drinking water stations and irrigation wells in 2015, and then analyzed chemically in water and soil fertility laboratory located in the irrigation ministry in Assiut. Aquachem software package was used to determine the groundwater type and rock source deduction. Piper-trilinear diagram was plotted to show the hydrochemical facies. Furthermore, Gibbs diagram was applied to determine the correlation between water composition and aquifer lithological characteristics. The results revealed that nearly all of the groundwater samples drop in the water-rock interaction field. The results of rock source deduction show that the ratio of Cl to the sum of anions is less than 0.8 for all samples, concluding that the rock weathering is dominant. According to the criterion of TDS values, 78% of all the samples indicated that the carbonate weathering is prevalent; in turn, the ratio of Mg to Ca plus Mg shows that limestone-dolomite weathering is predominant. These results confirm that the calcareous structural plateau surrounding the Nile aquifer along the Assiut governorate has an effect on the groundwater chemistry by interacting between groundwater and limestone rocks which are the main component of the calcareous plateau.