Groundwater quality evaluation of the alluvial aquifers using GIS and water quality indices in the Upper Blue Nile Basin, Ethiopia

Groundwater (GW), which contributes to the quality of life, economic development, improved food security, and rural society stability, is essential to improving rural water supply access and quality. Given its multi-purpose uses, GW quality has been degraded and polluted by global climate change, population growth, human activities, land use land cover (LULC) transition. GW quality, therefore, should be evaluated and tracked continuously to secure its multi-purpose uses. Herein, this study aims to assess the shallow GW standard using water quality indices (WQI) and GIS techniques in the northwestern boundary of Lake Tana, Upper Blue Nile (UBN) of the Amhara Region, Ethiopia. The water samples were collected from 30 sites, and physico-chemical parameters such as pH, electrical conductivity (EC) were measured in situ. Calcium (Ca+), magnesium (Mg+), sodium (Na+), potassium (K+), chlorine (Cl-), sulphate (SO4-2), nitrate (NO-3), bicarbonate (HCO3-), carbonate (CO3-2) concentraions were determined. Irrigation water quality indices, including sodium adsorption ratio (SAR), sodium soluble percentage (SSP), residual sodium carbonate (RSC), permeability index (PI), magnesium adsorption ratio (MAR), Kelley's ratio (KR), and Na% were calculated. The results show that EC (46.7%), SAR (97%), KR (53%), SSP (53.3%) MH (100%) and Na+ (50%) are suitable for irrigation. The overall WQI for drinking purposes ranges from 46 to 67.5, which confirms that 22%, 38.8%, and 39.2% of samples fall under very good, good, and poor quality, respectively. The hydrochemical facies indicated that, the dominant water type (43% of samples) is type-III (Na-K-Cl-SO4) and mixed type. Most shallow wells near Lake Tana are unsuitable for drinking purpose. Further, the government should monitor contamination sources, including agricultural activities, domestic wastes and landfills for sustainable GW quality.