Temporal variation of groundwater resources in Ilesa West Local Government, Osun State Nigeria

The study was carried out to investigate the different groundwater resources and to generate the temporal differences over the different seasons in Ilesa West Local Government, Osun State, Nigeria. The LGA has not been provided with municipal pipe-borne water supply for over 30 years, hence they are exclusively using groundwater in form of boreholes, dugwells and springs. The physico- chemical and heavy metal parameters were determined over a period of one year covering the rainy and dry seasons. A total of 69 drinking water points which comprises of 63 dugwells, 5 boreholes and 1 spring were used for the study and they were selected to represent the built-up part of the entire study area adequately. Parameters analysed were pH, electrical conductivity (EC), temperature, total dissolved solids (TDS), chloride, sulphate, nitrate, sodium, potassium (K), calcium, magnesium, hardness, alkalinity, bicarbonate using standard methods. Analysis of heavy metals (Fe, Cr) was carried out with atomic absorption spectrophotometer (AAS) and microbiological analysis was conducted using most probable number (MPN) of counting coliforms. The data generated were subjected to descriptive statistics and line graph. The analysis of the different groundwater resources revealed a good water quality but the values of pH, TDS, EC, K, were higher than the permissible range. The concentration of Fe and Cr is very high and could constitute some health hazards in some sources. The temporal variation of the water quality parameters did not follow any definite trend but the pH, NO3, TDS, HCO3, SO4, Fe, Cr were highest in the dry months of April and December, while Ca, Mg, K, Na, hardness, and alkalinity were highest in the rainy months of June and August. The percentage of microbial distribution was highest in the months of June in the boreholes and the spring but the distribution in the dugwells was entirely different. The water from the boreholes and dugwells were generally soft and should be checked for plumbo-solvency. It is recommended that a routine monitoring of all the sources should be carried out and a treatment that will reduce the heavy metals concentrations be enforced. Keywords: Groundwater resources, physico-chemical parameters, temporal variations, dugwells, boreholes and spring