Hydrogeochemical characterization and assessment of groundwater quality in Muyira Sector, Rwanda.

The Muyira sector is one of ten sectors of the Nyanza district in the Amayaga region of Rwanda. Amayaga region is part of the country's drought-prone areas, with high groundwater dependence. Most inhabitants in the area depend on groundwater for drinking and domestic purposes. Therefore, a hydrogeochemical characterization and assessment of groundwater quality in the study area was carried out using a combined application of hydrochemical models, multivariate statistical techniques, and GIS-based ordinary kriging interpolation on seven (7) borehole water samples. This study aimed to determine the concentrations and spatial distribution of various ions, groundwater quality issues, and the geochemical processes contributing to groundwater chemistry. The abundance of major cations in the groundwater is in the order Na⁺ > Ca²⁺ > K⁺ > Mg²⁺, whereas that of the major anions varies in the order HCO₃⁻ > SO₄²⁻ > Cl⁻. Ca-Mg-Na-HCO₃ water type is common in the area, possibly due to the dissolution of magnesite and silicate minerals in the basement rocks. Also, results indicate weak acids (i.e., HCO₃⁻) dominance over strong acids (i.e., SO₄²⁻ and Cl⁻). Ion exchange reactions and magnesite and silicate minerals weathering primarily control the area's groundwater chemistry. The results of the Pollution Index for Groundwater (0.29-0.55) and Groundwater Quality Index (29.14-53.68) indicate groundwater in the area is suitable for drinking. The sodium percentage (36.88–78.20%, mean of 57.83%), magnesium ratios (13.90–94.66, mean of 35.70), and sodium adsorption ratio (4.63–16.92, mean of 11.78) suggests that groundwater in the study area is suitable for irrigation purposes.