| Petroleum hydrocarbon contaminants frequently exist in both the vadose and saturated zones at petroleum hydrocarbon contaminated sites. Natural biodegradation of petroleum hydrocarbon contaminants occur in in situ reactive zones present in both the vadose and saturated zones. Biodegradation of petroleum hydrocarbon contaminants results in a mass discharge of gaseous biodegradation products through the vadose zone and dissolved gases and solutes in groundwater. While previous studies have focused either on transport of reactants, products, and geochemical indicators in groundwater or gaseous products in the vadose zone, this study examines both pathways for discharge of degradation products. Quantifying the mass discharge of the biodegradation products through these zones is important to estimate the rates of natural source zone depletion, assess the success of monitored natural attenuation, and quantify contaminant mass loss. In this study, mass discharge rates of biodegradation products via surface efflux (carbon dioxide and methane) and via groundwater (carbon dioxide, methane, and other intermediates) were quantified using field data. At the studied site, the surface efflux pathway through the vadose zone was found to be the dominant pathway for carbon loss. A discussion of the uncertainties associated with field and analytical methodologies allows identification of opportunities for future work. |
