Groundwater hydrocarbon contamination spatial pattern in Opuama, Western Niger-Delta, Nigeria

The impact of the phenomenon of incessant and protracted crude oil spillage into the subaerial environment of Opuama community in the Niger-Delta is an enduring concern. Of a greater concern is the possibility of deleterious hydrocarbon contamination of groundwater and the ensuing human health problems from consuming the same in this locality. An integrated data interpretation approach has been carried out through water sample analysis, terrain analysis, surface analysis and vegetation analysis using borehole water analysis data, Shuttle Radar Topographic Mission (SRTM) data, field point data and multispectral satellite imageries (Landsat 7 ETM+ and Landsat 8 OLI data) in a view to model the spatial pattern of the hydrocarbon contamination of the groundwater in the study area. This was with a view to ascertain the quality and safety of groundwater as a water source for domestic purposes in the oil impacted community and environs. Water samples were collected from the seven (7) available boreholes and analyzed with Gas chromatography coupled with Flame Ionization Detector (GC-FID). Polycyclic Aromatic Hydrocarbons (PAHs) detected showed exclusively light PAHs (up to four fused benzene rings) which are; Chrysene, Benzo(b)Fluoranthene, 2-MethylNaphthalene, Benzo(k)Fluoranthene and Phenanthrene. The total PAHs varied in concentration from 2958.4 to 27,508.0 µg/L. These high levels of PAHs can be attributed to the incessant spillage of crude oil on the wetland and continual interaction of the groundwater with the surface water that is perpetually bearing an oil-phase. Vegetation spectral analysis showed that the vegetation health of the study area has been negatively impacted by the oil pollution. The low vegetation index corroborated the extreme values of PAHs recorded in boreholes. Terrain as well somewhat affected the manner of pollution spread. The study concluded that the groundwater in the community was contaminated with light PAHs and the total PAHs concentration in this area by far exceeded the WHO maximum permissible limit of 10 µg/L and Nigerian Standard for Drinking Water Quality (NSDWQ) limit of 7 µg/L in drinking water. Hence the potability of the groundwater is compromised. The spatial variations in the levels of contamination in the study area determined by Kriging interpolation method are graded as mildly polluted (up to 28.6% of samples), very polluted (up to 14.3% of samples), highly polluted (up to 28.6% of samples), very highly polluted and extremely polluted (14.3% of samples above category). Another 14.3% of samples fall below the mildly polluted category.