ASSESSMENT OF GROUNDWATER QUALITY IN OSUN STATE SECRETARIAT, OSOGBO, SOUTH WESTERN NIGERIA
Some physico-chemical analyses of water samples from nine boreholes in Osun State Secretariat, Osogbo, South Western Nigeria were carried out. The aim of the study was to evaluate the stability of the ground water for drinking’ and other purposes. In all, nine (9) representative boreholes (BHs) were studied. Each of these has been designated by corresponding subscripts as BH1, BH2, BH3, BH4, BH5, BH6, BH7, BH8, and BH9 respectively. The range of values of the respective parameters obtained from the analysis were: temperature: 29.9-350c; pH: 4.7-7.1; PO3-4: 0.13-0.19mgl-1; mg: 5.0-26.0mgl1; NO-3: 0.02-17.omgl1; Cl: 0.4-56mgl1 ; fe2+: 0.01-5.0mgl-1and hardness: 8.0-146mgl-1. These analysis showed that the level of potability of the tested ground water is not generally acceptable when viewed against the National Agency For Food And Drug Administration And Control (NAFDAC), World Health Organisation (WHO), and National Primary Drinking Water Regulation (WPDWR) standards. The concentration level of fe2+ in BH1, BH2, and BH5 are above the recommended maximum permissible limit of 0.3mgl-1. The sources of Fe2+ in these boreholes may be due to the geology of the location because some of them are located on Ferruginized formations. It may also be due to quality of steel pipes used in the distribution of the water. The pH of the studied samples in the area falls within the range4.7-7.1 with a mean value of 5.5. This is generally below the ranges of 6.5-8.5, 7.0-8.5 and 6.5-8.5 for NAFDAC, WHO and united state NPDWR respectively. The pH value of almost all the water samples (88.9%) except bh3 fall within the acidic range (less than pH 7.0), suggesting that the geological formation of the area is acidic. The total hardness of the samples tested in the study varied from 8.0-146mgl-1. Only samples from BH1 and BH2 are moderately hard (75-150mgl-1) while others are purely soft waters(less than 75mgl-1).