M. Abbas*; A. Jardani; J.P. Dupont; N. Machour, 2017: An Application of Different Geophysical Methods for the Characterization of a Hydrocarbon Contaminated Site. Accepted in Near Surface Geophysics, 2017

(* Advised PhD student)

The hydrocarbon contamination, which can alter the physiochemical and biological properties of the subsurface, can be monitored by using geochemical analysis and integrated geophysical techniques. Electrical resistivity tomography, induced polarization, ground penetrating radar and self-potential methods were used in this work to characterize the hydrocarbon contamination and to investigate the geo-electrical properties of a site impacted by an aged hydrocarbon contamination. Throughout the investigation, the 2D geo-electrical measurements supported the conductive plume model and consistently recorded low resistivity anomalies and high chargeability values in the contaminated aquifers. Furthermore, the low resistivity anomalies were found to be coincident with regions of GPR attenuated reflections and significant negative self-potential anomalies associated with oxidation-reduction processes. These findings were supported by the geochemical measurements which revealed depleted concentrations of electron acceptors and elevated amounts of ions and total dissolved solids, which could be attributed to bacterial biodegradation of hydrocarbons. The extent of groundwater contamination was delineated according to the observed geophysical contrast between the contaminated and clean zones. The combination of the different geophysical methods constrained by geochemical point measurements provided insight on the different processes which might have modified the soil and groundwater biogeochemical properties

Revil, A., E. Atekwana, C. Zhang, A. Jardani, and S. Smith, 2012: A new model for the spectral induced polarization signature of bacterial growth in porous media. Water Resources Research., 48, W09545,doi:10.1029/2012WR011965. (pdf)

The complex conductivity of porous materials and colloidal suspensions comprises two components: an in-phase conductivity associated with electromigration of the charge carriers and a quadrature conductivity associated with the reversible storage of the charges at some polarization length scales. We developed a quantitative model to investigate the frequency domain induced polarization response of suspensions of bacteria and bacteria growth in porous media. Induced polarization of bacteria (alpha polarization) is related to the properties of the electrical double layer of the bacteria. Surface conductivity and a polarization are due to the Stern layer of counterions occurring in a brush of polymers coating the surface of the bacteria. These phenomena can be related to their cation exchange capacity. The mobility of the counterions in this Stern layer is found to be very small (4.7 1010 m2 s 1 V1 at 25 C). This implies a very low relaxation frequency for the a polarization of the bacteria cells (typically around 0.1–5 Hz), in agreement with experimental observations. This new model can be coupled to reactive transport modeling codes in which the evolution of bacterial populations are usually described by Monod kinetics. We show that the growth rate and endogenous decay coefficients of bacteria in a porous sand can be inferred nonintrusively from time-lapse frequency domain induced polarization data.