Characteristics of petroleum-contaminated groundwater during natural attenuation: a case study in northeast China

The objective of this study was to investigate a petroleum-contaminated groundwater site in northeast China. We determined the physicochemical properties of groundwater that contained total petroleum hydrocarbons (TPH) with a view to developing a scientifically robust strategy for controlling and remediating pollution of groundwater already contaminated with petroleum. Samples were collected at regular intervals and were analyzed for dissolved oxygen (DO), iron (Fe³⁺), sulfate (SO₄^2-), electrical conductivity (Eh), pH, hydrogen carbonate (HCO₃^-), and enzyme activities of catalase (CAT), peroxidase (HRP), catechol 1,2-dioxygenase (C12O), and catechol 2,3-dioxygenase (C23O). We used factor analysis in SPSS to determine the main environmental characteristics of the groundwater samples. The results confirmed that the study site was slightly contaminated and that TPH levels were decreasing slightly. Some of the physicochemical variables showed regular fluctuations; DO, Fe³⁺, and SO₄^2- contents decreased gradually, while the concentrations of one of the microbial degradation products, HCO₃^-, increased. Microorganism enzyme activities decreased gradually. The microbiological community deteriorated noticeably during the natural attenuation process, so microbiological degradation of pollutants receded gradually. The HCO₃^- content increased and the pH and Eh decreased gradually. The groundwater environment tended to be reducing.