Groundwater pollution from selected petroleum hydrocarbons in urban temeke district, Dar es Salaam

This study focused on the impact of petroleum hydrocarbons on the groundwater quality. Water samples were collected from both shallow and deep wells, from which benzene, toluene and xylene were determined by using Gas Chromatography (GC). The concentration levels of benzene, toluene and xylene in the boreholes range from 83.02 to 410.64 pg/L, 4.96 to 253.94 pg/L and 4.24 to 23.10 pg/L respectively. In the shallow well the concentration levels of hydrocarbons range from 57.29 to 388.75 pg/L, < 0.002 to 182.14 pg/L and < 0.004 to 76.19 pg/L respectively. Multivariate statistical analyses were used in data interpretation. Correlation analysis shows a negative correlation between TDS, electrical conductivity and temperature with the three determined hydrocarbons; these are non-polar compounds hence poor conductors of electrical currents. Weak positive correlation is observed between the three determined hydrocarbons. Sample clusters appeared to be influenced by mineral content of the groundwater. According to factor analysis, factor one shows to be highly loaded with conductivity, and TDS, while factor three shows to be enriched with temperature and negatively correlated with benzene. Factor two shows to be enriched with the three determined hydrocarbons and negatively correlated with pH, TDS and electrical conductivity, suggesting that anthropogenic activities in the area are the potential cause of this factor. Factors including hydro-geological structures, physico-chemical properties, microbial activities, relative amounts of the hydrocarbons in petroleum fuel mixtures and distance of the wells from the point source explain the variation and concentration levels of the hydrocarbons in the groundwater. It has been concluded that groundwater pollution by petroleum hydrocarbons is predominantly caused by industrial processes and traffic related activities taking place in the study area. Therefore, it is recommended that both shallow and deep wells be constructed at least 400 m away from the industrial area so as to avoid the risks of contamination from these pollutants.