Effect of Chemical and Mineralogical Composition of Rocks on the Groundwater Chemistry of Hewanie and its Surrounding Areas, Southern Tigray, Ethiopia

Abstract

The study was conducted in Hewanie and its surrounding areas of 169.82 km2 with a major objective of identifying the effect of chemical and mineralogical composition of rocks on the chemistry of the groundwater quality. This was conducted by taking 11 groundwater and 5 rock samples from the main geological units of the study area. Water samples were analyzed for major cations and anions, trace elements, TDS, total hardness, pH, electrical conductivity, and alkalinity the rock samples for major cations and anions and trace elements using AAS. The data was used to qualify and assess the quality of groundwater in the study area. Concentration of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^-, Cl^- and SO4^2- of groundwater samples in mg/l varied from 84 to 412, 96 to 211.2, 19.09 to 43.93, 2.34 to 51.09, 244 to 585.6, 71 to 340.8 and 49.49 to 122.5, respectively. Concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^-, Cl^- and SO₄^2- of rock samples in ppm varied from 2586.4 to 28540, 2575.8 to 5289.6, 28.83 to 6134.9, 190.3 to 2379, 293.74 to 3717.6, 433.1 to 1143.1, 2787.8 to 27849.6, respectively. The predominant cations trend in both the groundwater and rock samples the study area was Ca²⁺ > Mg²⁺ > Na⁺> K⁺. Therefore, it is concluded that the local rock chemistry is seriously affecting the groundwater chemistry.

Key words: Rock-water interaction, groundwater, rock, mineralogical composition, quality, Hewanie, Ethiopia.