Biogeophysics for Optimized Characterization of Petroleum-Contaminated Sites

Abstract

Oil spills are common occurrences on land and in coastal environments. To remediate oil spills, the contaminated volume has to be defined, appropriate remedial measures should be undertaken, and evidence must be provided for the successful remediation. Geophysical techniques can aid site investigation and remediation efforts. The insulating properties of hydrocarbons make them ideal targets for employing a variety of geophysical techniques for their characterization. Nonetheless, the geophysical response of hydrocarbon-contaminated sites is non-unique and depends on factors such as: (1) the release history, (2) hydrocarbon distribution and partitioning into different phases (vapor, free, dissolved, entrapped, and residual phases) in the unsaturated and saturated zones, (3) seasonal hydrologic processes, (4) extent of biodegradation and (5) aquifer salinity and host lithology. Where the contaminants have been biodegraded, the geophysical response depends on the by-products of different terminal electron acceptor processes (TEAPs). In this chapter, we review the different pathways by which TEAPs mediate geophysical property changes. We provide select field case studies from hydrocarbon-contaminated sites across the globe, including different climatic regimes and water salinity conditions. We show that the geophysical response can be transient, hence, data interpretation should be guided by an understanding of the hydrobiogeochemical processes at each site.