Spatial and Hydrochemical Characterisation of Groundwater Quality in Badagry Local Government Area, Lagos State, Nigeria

Groundwater is an important source of domestic water in coastal communities of southwestern Nigeria, where rapid urbanisation and intensive groundwater use may increase vulnerability to chemical deterioration and saline influence. This study assessed the spatial and hydrochemical characteristics of groundwater quality in Badagry Local Government Area (LGA), Lagos State, Nigeria. Seventy-two groundwater samples were collected from boreholes distributed across residential, crowded, commercial, industrial and coastal settings. In-situ measurements included pH and temperature, while total dissolved solids (TDS), hardness, major ions and selected metals were determined using standard analytical procedures. Descriptive statistics, comparison with Nigerian drinking-water standards, correlation analysis, hydrochemical classification and GIS-based spatial analysis were used to evaluate groundwater quality. Groundwater was generally soft and weakly mineralised, although substantial spatial variability occurred. Reported TDS ranged from 20.3 to 1,211 mg/L, with a mean of approximately 207 mg/L. The principal quality concern was acidity, with a reported mean pH of 5.59 and most samples below the Nigerian standard range of 6.5–8.5. Localised enrichment of TDS, salinity, nitrate, iron and manganese occurred at selected stations. Iron reached 0.346 mg/L, while manganese reached 0.825 mg/L. Chloride and sulphate remained below their respective national limits in the reported dataset. The spatial pattern indicates that groundwater chemistry reflects both natural water–rock interaction and local anthropogenic influences, with limited evidence of saline influence at selected coastal locations. The study demonstrates marked spatial heterogeneity in groundwater quality and identifies acidity and localised Fe and Mn enrichment as priority management concerns. Routine monitoring, source protection and treatment of acidic or metal-enriched groundwater are recommended.