Impact of oil and gas waste disposal on water and soil quality: A pilot study of Ngara & Bugungu waste consolidation sites in Buliisa District, Uganda

Abstract

Oil wastes from the exploration operations in the form of drilling muds, cuttings and chemicals contaminate the environment and threaten human health and ecosystems. The aim of this study was to assess the impacts of oil exploration wastes on water and soil quality around oil waste consolidation areas (WCAs) of Bugungu and Ngara in Buliisa district. The WCAs were located close to residential sites, agricultural farms and public water sources. A social survey was conducted to assess households’ awareness of the dangers associated with oil wastes. A total of 15 water samples and 32 soil samples were collected around Ngara and Bugungu WCAs and in control areas away from the WCS and tested for presence of Mn, Cu, Zn, Cr, Pb, Cd, and Fe. Trace elements from soil and water samples at WCAs and from the control area were analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The social survey revealed that around WCAs, there was a decline in the productivity of agricultural soils, change in the colour and quality of water collected from boreholes, streams and water wells. Soil samples tested revealed that the mean concentrations (mg /kg) of Cr (107.4), Fe (28071), Mn (1050), and Pb (20.8) in agricultural soils at WCAs and downstream areas were significantly higher than elemental concentrations (mg /kg) in control area which were 16.6 for Cr, 5013 for Fe, 143.5 for Mn, and 0.1 for Pb. In public water sources around WCAs and catchment areas, the concentrations of trace elements (mg /l) ranged between 0.6 and 8.8 for Fe; and 0.1-1.8 for Mn, higher than those at control area (0.1-0.2 mg/l) for Fe and national allowable limit of 0.3 mg/l for Fe and 0.1 mg/l for Mn in drinking water. In conclusion, oil wastes at Bugungu and Ngara WCAs appear to have contributed to contamination of public water sources and agricultural soils around the WCAs and their catchment areas in Buliisa district. There is need to conduct remediation of contaminated agricultural soils and sensitization of the households around WCAs on portable water sources and the dangers associated with cultivation of food crops in soils contaminated with oil exploration wastes.