Hadji D.S. Kallon1,2,4 *, Madhab Rijal1, 3

Groundwater is a major source of drinking water and is considered an imperative component of the accessible water assets across Sierra Leone and many parts of the world. The degradation of groundwater can jeopardize drinking water availability and human health. 29 groundwater monitoring samples with 16 water quality parameters were analyzed. Descriptive statistics, Piper plots, Arc GIS spatial interpolation, Gibbs plots, ion ratio analysis, Wilcox diagram, water quality index (WQI), and entropy-weighted water quality index (EWQI) were used to investigate the hydrochemical characteristics, controlling factors and evaluate the groundwater quality in the study area. The results revealed that the groundwater mean concentration of NO3 in the mining concession was 34.00 mg/L which was above the permissible limit, Ca2+ and HCO3 are higher in the Koidu community compared to the mining concession water, indicating weakly alkaline with dominant anions and cations of HCO3 and Na+ + K+ respectively, and the hydrochemical types were mainly HCO3·Ca2+ and HCO3 ·Na+. The order of anion concentration in groundwater was HCO3 > NOO3 > SO42− > Cl and HCO3 > SO42− > Cl > NO3 > Cl in the mining concession and the Koidu community respectively. Cations were Ca2+ > Na+, K+ > Mg2+ > Fe²⁺, and Ca2+ > Na+ > Mg2+ > K+ > Fe²⁺ in the mining concession and the Koidu community respectively. The interpretation of WQI and EWQI analysis exhibits 55.17% excellent, 17.24% good, 20.69% medium, 6.90% very poor, and 27.59% excellent, 24.14% good, 34.48% medium, 3.45% poor, and 10.34% very poor water respectively. Most of the sampling sites display similar trends to the WQI and EWQI. The solute source of groundwater was mainly controlled by water-rock interaction, cation exchange and the weathering of silicate and carbonate rocks were jointly the main contributors to the formation of the chemical components of groundwater in the study area, among which the main controlling factors of the groundwater were leaching, precipitate concentration and anthropogenic activities, and sulfate rock and carbonate rock dissolution. The overall water quality in the study area was suitable for human consumption but was polluted to an insignificant extent by mining activities. This study provides theoretical support and a decision-making basis for developing, utilizing, and protecting water resources in the study area.

Keywords: Diamond Mining, Controlling factors, Hydrochemical facies, Water Quality Index

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