Determination of the contamination profile of groundwater in the vicinity of petroleum products retailing stations in Nigeria

The quality of groundwater in the vicinity of petroleum products retailing stations in Ile-Ife, Nigeria was investigated with a view to providing valuable information on the organic and other physico-chemical parameters associated with the contamination of the groundwaters by petroleum products. The paper aims to discuss these issues.

Three sets of samples were collected per season from artesian wells within petroleum products retailing stations for polycyclic aromatic hydrocarbons (PAHs), trace metals and other physico-chemical parameters analysis. Extraction, cleaned-up and concentration of the PAHs were done using certified analytical methods. Levels of the PAHs and metals were determined using gas chromatography coupled with flame ionization detector and bulk scientific atomic absorption spectrophotometer, respectively, while other pollution indicators were measured using standard analytical procedures.

The groundwaters contained elevated levels of PAHs, Cu, Zn, Mn, Pb, Cr, V, Ni, Fe and total dissolved solids than their maximum allowable limits for drinking water. Analysis of variance (ANOVA) results confirmed that both seasonal variation and location had much influence on the levels of most of the analyzed parameters. Some of the parameters showed strong positive correlation with each other, while Cr/Pb and Na/Pb displayed strong negative correlation with each other, indicating similar source(s) and/or chemical affinity and vice versa, respectively. Cross-plot analysis results using metals and PAHs concentrations as variables showed significant positive correlations (R2=0.99) and (R2=0.60), respectively, suggesting similar source(s) of contamination of the two sets of samples.

The level of the groundwater contamination was an indication of indiscriminate discharge of petroleum products and/or underground tank leakage within the study areas.