Assessing uncertainty in remediation by natural attenuation of a petroleum hydrocarbon contaminated site

Over the past decade, natural attenuation has been accepted as a feasible remediation alternative for sites contaminated with petroleum hydrocarbons. Remediation by natural attenuation relies on the physical, chemical and biological processes that contribute to decrease both contaminant concentration and plume size. Extensive analysis of these intrinsically occurring processes is required to assess the time required for cleanup and the extent of future migration of the contaminant plume. A number of protocols, guidance documents and models have been developed for assessing the viability of the technology on a site-specific basis. These tools, have not however, fully addressed the uncertainty associated with field characterization of these processes and mechanisms. In this paper, we determine the potential impacts of uncertainties associated with hydrogeological and geochemical characterizations of the groundwater system and the uncertainties associated with the source term. The implications for remediation by natural attenuation are determined through analytical modelling using different values for key model parameters. The uncertainty modelling is used to demonstrate the feasibility of using natural attenuation at a coastal site contaminated by refined and crude BTX (benzene, toluene and xylene).