275-4 Hydrogeochemical Characterization and Quality Assessment of Groundwater in the Water-Stressed Drought-Prone Southeastern Region of Rwanda.

Session: Advancing the Understanding and Management of Groundwater Pollution with Arsenic and Other Geogenic Contaminants Using Geospatial Tools, Machine Learning, and Data Science, Part II

Presenting Author:

Emmanuel Ngendahayo

Authors:

Ngendahayo, Emmanuel¹, Nilsson, Erik², Larson, Magnus³, Nsabimana, Antoine⁴, Bhattacharya, Prosun⁵, Persson, Kenneth M.⁶

(1) Building and Environmental Technology, Lund University, Lund, Skåne, Sweden; Chemistry, University of Rwanda - College of Science and Technology (UR-CST), Kigali, Rwanda, (2) Building and Environmental Technology, Lund University, Lund, Sweden, (3) Building and Environmental Technology, Lund University, Lund, Sweden, (4) Biology, University of Rwanda - College of Science and Technology (UR-CST), Kigali, Rwanda, (5) Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden, (6) Building and Environmental Technology, Lund University, Lund, Sweden,

Abstract:

Groundwater is a vital resource in drought-prone southeastern Rwanda, where limited surface water availability places high demand on aquifers for drinking, livestock farming, and small-scale irrigation. However, comprehensive assessments of groundwater quality and the underlying hydrogeochemical processes influencing its chemistry remain scarce. This study presents an integrated hydrogeochemical evaluation of 165 shallow, phreatic boreholes sampled between 2022 and 2025 across approximately 10,000 km² of water-scarce areas in southeastern Rwanda. Field and laboratory analyses determined the concentrations of key physico-chemical parameters and major ions, with data analysed and interpreted using multivariate statistics, geochemical modelling, hydrochemical diagrams, and GIS-based mapping. Principal Component Analysis revealed four main factors explaining 74% of the total variance, likely reflecting natural mineral dissolution, evaporite weathering, carbonate buffering, and anthropogenic pollution. Piper and Gibbs diagrams revealed spatial variations in hydrochemical facies, with Ca-HCO₃ water type dominating upstream, whereas Na-HCO₃ and Na-Cl types prevailed downstream, suggesting influences of rock-water interaction and evaporation, respectively. Groundwater quality was assessed using an Integrated Water Quality Index (IWQI), which combined expert judgment and entropy weighting. Irrigation suitability was evaluated using Sodium Adsorption Ratio (SAR) and Sodium Percentage (Na%). The computed weights indicated that the IWQI effectively balanced expert judgment on the health risks posed by chemical components with the objective data derived from ion concentration variability. Based on the IWQI, groundwater in the study area was generally of good quality and suitable for various uses. However, 10.2% of the boreholes fell into the medium to poor quality category, making them unfit for drinking. Additionally, 18.2% of the boreholes posed a risk for irrigation use, due to salinity-related hazards to agricultural lands. This study offers a valuable baseline for groundwater quality monitoring by evaluating current water quality conditions and identifying related health risks, emphasizing the need for continuous water quality assessment to guide sustainable resource management across the country. Moreover, the sensitivity analysis of IWQI demonstrated that the IWQI offers a reliable and broadly applicable tool for assessing overall water quality, with valuable insights for policymakers and stakeholders in drought-prone areas.

Keywords: Groundwater quality. Hydrogeochemical processes. IWQI. Drought-prone areas. Southeastern Rwanda.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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