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

Abstract

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.

Keywords:

• Groundwater quality
• isotopes
• nitrate
• environmental pollution
• risk assessment

Acknowledgments

The authors express their gratitude to colleagues at Ministry of Irrigation and Water Resources, Groundwater water and Wadis General Directorate, Sudan, who helped in the field works. Thanks are also extended to the staff at Department of Electricity and Renewable Energies, Ministry of Energy and Mines, Rabat, Morocco, as well as the International Atomic Energy Agency (IAEA), Vienna, Austria, for isotope analysis services.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through General Research Project under grant number [GRP-111–41].