Isotopic and chemical facies for assessing the shallow water table aquifer quality in Goly Region, White Nile State, Sudan: focusing on nitrate source apportionment and human health risk

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Groundwater from the shallow water table aquifer is the main supply of drinking water for residents in Goly Region, White Nile State, Sudan. The residents have complained about groundwater quality. This study aims to evaluate groundwater quality in in Goly Region and to assess the possible health risk of toxicants with focusing on nitrates. The study examined groundwater from wells distributed in 23 sites for hydrogeological, physiochemical, and isotopic facies. The ranges of facies levels (mg/L) were as follows: nitrate (6.2–655.6), fluoride (0.00–2.16), sodium (36.4–293.2), total dissolved solids (349–908), carbonate (0.00–24.0), nitrite (0.026–0.828), sulfate (1.00–77.00), ammonia (0.00–0.40), and chloride (12.78–42.60), besides pH (6.93–8.48). According to the National Sudanese Guidelines and the World Health Organization guidelines, 12 wells recorded unhealthy levels for nitrate, 1 well recorded unhealthy level for fluoride, and 2 wells recorded unhealthy levels for sodium, while all wells recorded healthy levels for the rest of facies. Additionally, groundwater consumption from 14 sites put both children and adults at potential health risk from nitrates based on hazard risk index. The Piper diagram shows that the trend of cation exchange in the aquifer was from (calcium + magnesium) to (sodium + potassium). Significant positive correlations were observed between several parameters, e.g. the combinations of static water level-depth (0.51), electrical conductivity (EC)-nitrate (0.60), EC-sulfate (0.73), EC-fluoride (0.55), EC-chloride (0.76), EC-sodium (0.84), pH-fluoride (0.73), and pH-sodium (0.59). The principal component analysis of the examined facies shows that the first two principal components, which have similar loadings (≈ 22% of each), represented natural and anthropogenic sources of major ions. The isotopes levels and relationship of δ15N and δ18O revealed that nitrate contamination was from animal waste and/or sewage. The relation between δ18O and δ2H isotopes of water demonstrates that groundwater samples were deviated from Meteoric Line of the Sudan and Global Meteoric Water Line.