Hydrogeochemical categorization and quality assessment of shallow groundwater sources in typical urban slum and peri-urban areas of Ibadan, Southwest Nigeria

The present study appraises the quality and hydrogeochemical characterization of groundwater from shallow hand-dug wells in parts of Ibadan, Nigeria. Ten (10) composite water samples were collected from two representative residential locations in the city, one is a densely built up area (BUA) and the other is a peri-urban area (PUA). The dominant factors influencing hydrogeochemical characteristics and water quality assessment of the groundwater samples were investigated using physico-chemical variables, calculations of ionic ratios, water quality index (WQI) and Larson-Skold (L-S) index. Results show that the water samples are slightly acidic in the two residential communities. The order of abundance in major cations and anions are: Na+>Ca2+>Mg2+>K+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Na^{ + } > Ca^{2 + } > Mg^{2 + } > K^{ + }$$\end{document} and HCO3-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$HCO_{3}^{ - }$$\end{document} > Cl-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Cl^{ - }$$\end{document} > SO42-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$SO_{4}^{2 - }$$\end{document} > NO3-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$NO_{3}^{ - }$$\end{document}, respectively, in both BUA and PUA. The geochemical results revealed that groundwater in both locations are freshwater with < 15 meq/l of chloride, < 60 meq/l of sulfate, predominantly NaHCO3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$NaHCO_{3}$$\end{document} type and shallow meteoric water percolation type. The hydrochemical data, ionic ratios and chloro-alkaline index (CAI) values suggest that the likely processes influencing hydrochemistry in the study area are carbonate dissolution/silicate weathering, cation exchange and little of anthropogenic activities. The results of WQI elucidate that the quality of PUA water is better for drinking than that at of BUA water. Comparison of hydrochemical data with World Health Organization (WHO) permissible limits showed that all analyzed groundwater samples are suitable for domestic and industrial uses. Wells 1 and 2 (S1 and S2) in BUA had high values of Na+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Na^{ + }$$\end{document} above permissible limit while all samples in BUA and PUA had dissolved oxygen (DO) values below the WHO permissible limit of 5 mg/l. The micro scale study will assist in proper management of groundwater resources based on urban development pattern and provide suitable reference base for preservation of the groundwater resource and prevent environmental risk.