Hydrogeochemistry of shallow groundwater in Ado-Ekiti Area, Southwestern Nigeria

Abstract

This study examined the hydrogeochemistry of shallow groundwater in Ado-Ekiti Area, Southwestern Nigeria with a view to elucidating the suitability for domestic and agricultural activities. Twenty seven shallow wells' and three boreholes’ water were randomly sampled and subjected to physico-chemical and bacteriological analyses using standard methods. In-situ parameters (temperature (°C), pH and electrical conductivity (μS/cm)) were measured with Multi-parameter Testr™ 35 Series S/N: 1382654 while turbidity measurement was through the use of turbidity tubes. Major ions were analyzed spectrophotometrically except for HCO3− that was determined by titration while bacterial determination was carried out using membrane filtration method. The pH in porphyritic granite (PG) (av. 7.16), fine grained granite (FG) (av. 7.10) and migmatite (MG) (av. 7.51) were within approved standard for drinking water but weakly alkaline. All mean values of EC (μS/cm) on PG, FG and MG (421.11, 412.00 and 206.77), total dissolved solid (TDS) (mg/L) (315.85, 309.00 and 155.08), total hardness (TH) (mg/L) (133.92, 146.50 and 133.12) and turbidity (NTU) (3.73, 1.00 and 4.35) respectively fell within approved standard of drinking water. The order of anions abundance in the groundwater was Cl− > HCO3− > SO42− > NO3− > PO43− while that of the cations was Ca2+>Na+>Mg2+>K+. All sampled water tested positive to bacteriological analysis indicating that there was a greater risk that pathogens were present in the groundwater warranting its treatment before drinking. Characterization of groundwater of the study area revealed the dominance of Ca(Mg)–Cl(SO4) water type with Ca–Cl and Ca–HCO3 water types in the minority. Irrigation quality evaluation indicated that the groundwater system was suitable for irrigation purposes. The groundwater of the study area was low mineralized, with low residence time, chemically potable but bacteriologically infected. Rock types had significant influence on the ionic concentrations of the groundwater with more dissolved ions occurring in porphyritic granite.