Stable Carbon Isotope Biogeochemistry of a Shallow Sand Aquifer Contaminated with Fuel Hydrocarbons


Ground-water chemistry and the stable C isotope composition (δ13C(DIC)) of dissolved inorganic C (DIC) were measured in a sand aquifer contaminated with JP-4 fuel hydrocarbons. Results show that ground water in the upgradient zone was characterized by DIC content of 14-20 mg C/L and δ13C(DIC) values of -11.3‰ to -13.0‰. The contaminant source zone was characterized by an increase in DIC content (12.5 mg C/L to 54 mg C/L), Ca, and alkalinity, with a significant depletion of 13C in δ13C(DIC) (-11.9‰ to -19.2‰). The source zone of the contaminant plume was also characterized by elevated levels of aromatic hydrocarbons (0 μg/L to 1490 μg/L) and microbial metabolites (aromatic acids, 0 μg/L to 2277 μg/L), non-detectable dissolved O2, NO3 and SO4. Phospholipid ester-linked fatty acid analyses suggest the presence of viable SO4-reducing bacteria in ground water at the time of sampling. The ground-water chemistry and stable C isotope composition of ground-water DIC are interpreted using a chemical reaction model involving rainwater recharge, contributions of CO2 from soil gas and biodegradation of hydrocarbons, and carbonate dissolution. The major-ion chemistry and δ13C(DIC) were reconciled, and the model predictions were in good agreement with field measurements. It was concluded that stable C isotope measurements, combined with other biogeochemical measures can be a useful tool to monitor the dominant terminal electron-accepting processes in contaminated aquifers and to identify mineralogical, hydrological, and microbiological factors that affect δ13C of dissolved inorganic C.


Geosciences and Geological and Petroleum Engineering


United States. Environmental Protection Agency
Strategic Environmental Research and Development Program (U.S.)


EPA cooperative agreement #CR824184

Keywords and Phrases

Carbon Isotope; Environmental Monitoring; Hydrocarbon; Marine Environment; Biogeochemistry; Carbon; Groundwater Pollution; Isotopic Composition; Sand

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Article - Journal

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