Assessment of groundwater quality for irrigation purposes in ilesha West local government, Osun State, Nigeria

This study assessed the suitability of different groundwater resources in a basement complex of Ilesha West Local Govt. Area (LGA) for irrigation purposes. A total of 207 water samples were collected from hand-dug wells, boreholes and springs during the peak periods of wet and dry seasons. The physicochemical characteristics (pH, total dissolved solids (TDS), electrical conductivity (EC), Alkalinity, Hardness), basic cations, anions (Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, Cl-, NO3-) and heavy metals (Pb2+, Cr2+, Fe2+ and As5+) present were determined. The results were subjected to irrigation quality models such as sodium adsorption ratio (SAR), Kelly ratio (KR), sodium hazard (SH), permeability index (PI) and magnesium hazard (MH). To reveal the hydro-geochemical facies of the groundwater, Piper and Durov diagrams were plotted using the geochemist workbench sheet (GWB) software. A maximum SAR value of 6.0197 was recorded in the hand-dug wells during the dry season and the mean concentration of Cr2+ was observed to be higher than the recommended limits for irrigation. The percentage suitability of the water sources for irrigation purposes are 76%, 94%, 46% and 96% for SH, PS, KR, and MH models, respectively. Piper and Durov's diagrams revealed Na++ K+ (80%), Ca+ (90%) and HCO3- + CO3 -, Cl-. as the dominant cations, and anions respectively. Additional Hydro-geochemical plots revealed intermixing of the cations and anions, suggesting the dissolution of carbonate and silicate minerals from the parent soil or rock. Generally, the groundwater in the study area is suitable for irrigation, but the sustainability based on quantity should be investigated.