Assessment of Groundwater Quality within Asa and Oyun River Basins South Western Nigeria Using Water Quality Index

Ensuring that the groundwater consumed by the growing population of Nigeria meets the appropriate quality is of utmost importance. The use of various evaluation techniques such as the Water

Quality Index becomes necessary. The use of water quality index to evaluate the quality of groundwater in hand dug wells within Asa and Oyun River Basins of South Western Nigeria has been carried out in this study. 20 samples were obtained from Asa and Oyun River basin (10 samples from each). Analysis was carried out for twelve physico-chemical parameters. These parameters which were used for Water Quality Index determination include: pH, total dissolved solids (TDS), Nitrate (NO¯ 3), Sulphate (SO4 2), Carbonate (CO3), Zinc (Zn), Chlorine (Cl), Potassium (K), Copper (Cu), Lead (Pb), Arsenic (As) and Chromium (Cr) The Water Quality Index (WQI) values ranged between 0.09 and 943.25 for samples obtained within Asa river basin and between 0.04 and 198.73 for samples obtained within the Oyun river basin. Classifying WQI values <100 as potable and >100 as non-potable, 5 samples within the Asa River basin is classified as potable while 5 is non-potable. 9 samples within the Oyun river basin are classified as potable and only 1 is non-potable.

The high WQI values from the sampling location are observed to be due to higher values of dissolved solids, Nitrate, Lead and Arsenic. The study reveals that 70% of the total of 20 groundwater samples investigated within Asa and Oyun River basins is potable, this can be consumed without treatment, While 30% is non-potable. However, the sources identified as unsafe would require treatment before consumption.