Natural Attenuation of Hydrocarbon Compounds in Groundwater

Abstract

Natural attenuation (NA), also termed intrinsic bioremediation, is the application of engineering principles to the performance of soils and aquifers as in situ bioreactors to transform pollutants to less harmful forms, thereby reducing environmental risk. Processbased conceptual models describe the development of solute plumes in aquifers and the biodegradation processes which reduce contaminant loads during transport towards sensitive receptors. Mass and electron flux balance calculations are used to quantify microbial transformation rates and estimate plume lifetimes. More extensive site data sets and numerical modeling of reactive transport provide additional insight into NA processes and the engineering performance of the in situ reactor system to achieve remediation objectives. Current performance assessment approaches for NA are data intensive, essentially empirical and reliant on extensive and costly site-specific investigations. Research needs include improved site investigation tools to parameterize microbial process rates and also more advanced data sets, and theoretical frameworks to interpret and extrapolate the contribution of microbial function and activity to NA performance.