Comparing Migration Pathways of Biodegradation Products from Petroleum Hydrocarbon Natural Attenuation

Abstract:

Petroleum hydrocarbons contaminants frequently exist in both the vadose and saturated zones at contaminated fuel sites. Natural biodegradation of petroleum hydrocarbon contaminants occur in in situ reactive zones present in both the vadose and saturated zones. Biodegradation of petroleum hydrocarbons results in a mass discharge of gaseous biodegradation products through the vadose zone and transport of dissolved gases through the saturated zone. While previous studies have focused solely on transport of degradation products or geochemical parameters in groundwater or efflux of gaseous byproducts from 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 attenuation, assess the success of monitored natural attenuation, and quantify and document contaminant mass loss. In this study, surface efflux and groundwater mass discharge rates of biodegradation products (carbon dioxide, methane, and other intermediates) were quantified using field data. Field and analytical methodologies will be presented along with the results of the data analysis and a discussion of the uncertainties. Based on the data analysis, the surface efflux pathway through the vadose was found to be the dominant pathway for carbon loss at the monitored field site.