Assessment of Heavy Metal Contamination in Groundwater around Waste Dumpsites: A Case Study of Oyo State Waste to Energy Plant - Ajakanga, Oluyole Local Government, Ibadan, Oyo State, Nigeria

Abstract

This study assessed selected heavy metal concentrations and pollution status in leachate and groundwater around the Oyo State Waste-to-Energy Plant, Ajakanga, Oluyole Local Government Area, Ibadan, Oyo State, Nigeria. Eight sampling points were investigated, comprising three shallow wells, three boreholes, and two leachate samples. Water samples were collected in clean plastic bottles, acid-preserved, filtered, and analysed for nickel, lead, iron, copper, chromium, cadmium, and arsenic using flame atomic absorption spectroscopy. The measured concentrations were compared with drinking-water guideline values, while the contamination factor and pollution load index were used to evaluate the degree of heavy metal contamination across the sample categories. The results showed that iron was the dominant metal in all sample categories, with the highest concentrations recorded in leachate samples at 22.956 mg/L and 56.234 mg/L. Iron concentrations in shallow wells and boreholes also exceeded the Nigerian drinking-water limit of 0.3 mg/L. Copper occurred at lower concentrations, with higher values in leachate than in groundwater, while nickel, lead, chromium, cadmium, and arsenic were generally very low or below detection limits. The pollution load index values were 0.063 for shallow wells, 0.062 for boreholes, and 0.164 for leachate, indicating low overall heavy metal pollution load. However, the high iron contamination factor, particularly in leachate and shallow wells, indicates localised contamination and possible influence from waste-derived leachate. The findings provide baseline information on groundwater quality around the facility and support the need for improved leachate control, routine monitoring, and periodic assessment of nearby groundwater sources.