Geophysical Signatures of Microbial Activity at Hydrocarbon Contaminated Sites: A Review

Abstract

Microorganisms participate in a variety of geologic processes that alter the chemical and physical properties of their environment. Understanding the geophysical signatures of microbial activity in the environment has resulted in the development of a new sub-discipline in geophysics called ''biogeophysics''. This review focuses primarily on literature pertaining to biogeophysical signatures of sites contaminated by light non-aqueous phase liquids (LNAPL), as these sites provide ideal laboratories for investigating microbialgeophysical relationships. We discuss the spatial distribution and partitioning of LNAPL into different phases because the physical, chemical, and biological alteration of LNAPL and the subsequent impact to the contaminated environment is in large part due to its distribution. We examine the geophysical responses at contaminated sites over short time frames of weeks to several years when the alteration of the LNAPL by microbial activity has not occurred to a significant extent, and over the long-term of several years to decades, when significant microbial degradation of the LNAPL has occurred. A review of the literature suggests that microbial processes profoundly alter the contaminated environment causing marked changes in the petrophysical properties, mineralogy, solute concentration of pore fluids, and temperature. A variety of geophysical techniques such as electrical resistivity, induced polarization, electromagnetic induction, ground penetrating radar, and self potential are capable of defining the contaminated zones because of the new physical properties imparted by microbial processes. The changes in the physical properties of the contaminated environment vary spatially because microbial processes are controlled by the spatial distribution of the contaminant. Geophysical studies must consider the spatial variations in the physical properties during survey design, data analysis, and interpretation. Geophysical data interpretation from surveys conducted at LNAPL-contaminated sites without a microbial and geochemical context may lead to ambiguous conclusions.

Theoretical Developments in Electromagnetic Induction Geophysics with Selected Applications in the Near Surface

“…Recently, Atekwana and Atekwana (2010) have reviewed advances in applications of the electrical and electromagnetic geophysical techniques to understanding biogeophysical signatures at LNAPL (light non-aqueous phase liquids) contaminated sites. A discussion on the physical and chemical basis for observable geophysical signatures from subsurface LNAPL distributions (Fig.…”

Applying FDEM, ERT and GPR at a site with soil contamination: A case study

“…With applications of geology, geochemistry, microbiology and sampling and analysis, they are often employed in soil and groundwater contamination investigations (Atekwana and Atekwana, 2010). GPR has proven its ability to provide high-resolution images for strata.…”

Field GPR monitoring of biostimulation in saturated porous media

“…In recent years, contaminated aquifers and associated biodegradation have become subjects for geophysical investigations (Atekwana and Atekwana, 2010;Atekwana and Slater, 2009). Laboratory research and petrophysical modeling combined with field studies have shown that when contaminant hydrocarbons displace water, the electrical conductivity (σ) of the porous media will decrease (Endres and Redman, 1996;Lien and Enfield, 1998).…”