Radiocarbon and Stable Carbon Isotope Analysis to Confirm Petroleum Natural Attenuation in the Vadose Zone

Abstract

CO2 and CH4 radiocarbon and stable carbon isotope ratios were used to assess natural attenuation at a fuel-contaminated soil site at the Norfolk Navy Base, Norfolk, VA (USA). Soil gas samples were collected spatially over a monitoring network in October 2002 and in March 2003. CO2 and CH4 from regions with high petroleum concentrations were 14C-depleted relative to uncontaminated areas. 14C-depleted methane suggested methanogenic hydrocarbon degradation. The difference in CO2 age between background and plume-influenced areas indicated that approximately 90% of the CO2 at the latter was petroleum derived, making contaminant the primary source of carbon for the microbial assemblage.