ANTHROPOGENIC AND HYDROGEOLOGICAL CONTROLS ON GROUNDWATER QUALITY IN BADAGRY LOCAL GOVERNMENT AREA, LAGOS STATE, NIGERIA

Groundwater is an important source of domestic water supply in Badagry Local Government Area (LGA), Lagos State, but its quality may be affected by the interaction between aquifer characteristics and increasing anthropogenic pressure. This study assessed the hydrochemical characteristics of groundwater and examined their relationships with selected hydrogeological and anthropogenic factors in Badagry LGA. Seventy-two boreholes distributed across residential, high-density, coastal, industrial and commercial environments were investigated. Field measurements included pH, temperature, electrical conductivity (EC) and total dissolved solids (TDS), while laboratory analyses covered major ions, total hardness, nitrate, iron and manganese. Borehole depth, static water level, ground elevation and groundwater elevation were also assessed. Potential contamination sources, including septic systems, solid-waste disposal, wastewater discharge, industrial activities, agricultural activities, markets, mechanic workshops and drainage conditions, were documented and their proximity to sampled boreholes determined using GIS. Groundwater was predominantly acidic, with pH ranging from 4.00 to 6.90 and a mean of 5.59 ± 0.84; 79.2% of the samples had pH below 6.5. TDS ranged from 20.3 to 1211 mg/L, with a mean of 191.0 ± 194.1 mg/L, while total hardness remained relatively low (27.71 ± 15.19 mg/L). Nitrate ranged from 0.01 to 55.40 mg/L, iron from 0.002 to 0.825 mg/L and manganese from 0.002 to 0.307 mg/L. Please specify the statistical test used (e.g., ANOVA, Kruskal-Wallis) and report the test statistic, degrees of freedom, and p-value for the comparisons of total hardness and nitrate across land-use categories. If multiple comparisons were performed, indicate the correction method applied. Septic systems/pit latrines represented the most widespread anthropogenic pressure, affecting 80.6% of sampled boreholes, followed by poor drainage and solid-waste disposal. Please describe the method used to classify hydrochemical facies, such as plotting on a Piper diagram and using the dominant cation and anion (e.g., >50% meq/L) to assign the facies. Also, specify the software or manual calculation used. The hydrochemical composition indicates contributions from mineral weathering and ion exchange, with possible localized saline influence in coastal locations. The findings indicate that groundwater quality in Badagry is characterised by widespread acidity and localized enrichment of selected constituents. Improved sanitation, better solid-waste management, protection of boreholes from nearby contamination sources and routine groundwater monitoring are recommended for sustainable management of the coastal aquifer.