Combined C-14 and delta C-13 analysis of petroleum biodegradation in a shallow contaminated aquifer

摘要

The contamination of soil and groundwater by the accidental release of petroleum hydrocarbons is a common problem that affects drinking water supplies, and in situ biodegradation is a promising option for removing contaminants, with relatively low costs and minimal health risks. Total petroleum hydrocarbons (TPH), delta C-13 and C-14 isotope ratios in dissolved inorganic carbon (DIC), and other geochemical indicators have been analyzed to demonstrate the effectiveness of in situ biodegradation at a contaminated site. The delta C-13 and C-14 isotope ratios ranged from -5.4 to -18.4 % and from 35.1 to 67 pmc, respectively. Some groundwater samples were contaminated with petroleum hydrocarbons with low C-14 and delta C-13 contents, indicating the existence of microbial non-methanogenic biodegradation, whereas low C-14 and high delta C-13 contents were associated with the highest TPH concentrations, confirming that microbial methanogenic biodegradation occurred in these areas. Differences in the delta C-13 and C-14 isotope ratios between monitoring wells in uncontaminated and contaminated areas suggest that the percentage of the DIC produced by methanogenic biodegradation decreased from 28.5-32.0 to 5.94-6.67 % along the flow direction, and became almost zero in downgradient areas and at the edge of the contamination plume.