Temporal Geophysical and Geochemical Signatures Due to Contaminant Source Reduction at Wurtsmith Airforce Base in Oscoda Michigan, USA

Geophysical investigations have documented characteristic changes (e.g., higher bulk electrical conductivity, positive self potential (SP), attenuated ground penetrating radar (GPR) reflections) associated with hydrocarbon biodegradation in field experiments. These characteristic geophysical signatures result from biogeochemical transformations of the bulk properties of the contaminated relative to uncontaminated media. In this study, we present the results of surface geophysical surveys acquired in 1996, 2003, and 2007 that document changes in geophysical signatures associated with removal of hydrocarbon mass in the contaminated zone. Initial investigations in 1996 showed that relative to background, the contaminated area was characterized by higher bulk electrical conductivity, positive SP anomaly, and attenuated GPR reflections. Repeated surveys in 2003 and 2007 over the plume showed that in 2007, the bulk electrical conductivity had reverted to near background conditions, the positive SP anomaly became more negative, and the zone of attenuated GPR reflections showed increased signal strength. The removal of hydrocarbon mass in the vadose zone over the plume by a soil vapor extraction system installed in 2001 was primarily responsible for the changing geophysical responses. Although chemical data from groundwater showed a 3 m thick conductive plume in 2007, the plume was not imaged by electrical resistivity. Forward modeling suggests that the apparent bulk electrical conductivity of the saturated zone plume has to be 4-5 times higher than background values to be imaged by electrical resistivity. We conclude that hydrocarbon contaminant mass reduction by natural or engineered (bio)remediation can be effectively imaged by temporal geophysical surveys.Boone Pickens School of Geolog

Temporal Geophysical Signatures from Contaminant-Mass Remediation

We have previously documented changes in bulk electrical conductivity, self-potential (SP), and ground-penetrating-radar (GPR) reflections in a field setting caused by biogeochemical transformations of hydrocarbon-contaminated media. These transformations are associated with hydrocarbon biodegradation. The results of surface geophysical surveys acquired in 1996, 2003, and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone. Initial investigations in 1996 showed that relative to background, the contaminated area was characterized by higher bulk electrical conductivity, positive SP anomaly, and attenuated GPR reflections. Repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007, the bulk electrical conductivity had reverted to near-background conditions, the positive SP anomaly became more negative, and the zone of attenuated GPR reflections showed increased signal strength. Removal of hydrocarbon mass in the vadose zone over the plume by a soil vapor-extraction system installed in 2001 was primarily responsible for the changing geophysical responses. Although chemical data from groundwater showed a 3-m-thick conductive plume in 2007, the plume was not imaged by electrical resistivity. Forward modeling suggests that apparent bulk electrical conductivity of the saturated zone plume has to be three to five times higher than background values to be imaged by electrical resistivity. We suggest that removing hydrocarbon-contaminant-mass reduction by natural or engineered bioremediation can be imaged effectively by temporal geophysical surveys

GEOCHEMICAL SIGNATURES DUE TO CONTAMINANT SOURCE REDUCTION AT

thesis and introduces the problem. This section also presents the 1 journal paper. Paper 1 “Temporal geophysical signatures due to contaminant source reduction ” which focuses on the geophysical signatures was submitted to GEOPHYSICS for review and is currently being revised. Paper 2 describes the impacts of biodegradation and weathering products over time at the FT-02 site in Oscoda, Michigan is still being revised for submission. Section two summarizes the major conclusions of the work iii ACKNOWLEDGMENTS I thank God almighty for His abundant and never ending blessings. I will also like to thank my advisors Dr. Estella Atekwana and Dr. Eliot Atekwana for their guidance, assistance, patience, encouragement, inspiration and friendship throughout my Masters program. I have learnt so much from them and I am very grateful for the knowledge they imparted to me. Also I will like to thank Dr. Anna Cruse for her suggestions and corrections. I will also like to thank Dr. Dale Werkema from the Environmental Protection Agenc

Geophysical and Geochemical Attenuated Signatures Associated with Hydrocarbon Contaminated Site Undergoing Bioremediation

Previous geophysical investigations (1996, 2003, and 2004) conducted at the decommissioned Wurtsmith Air Force Base former Fire Training Cell (FT-02) showed a clearly defined high conductivity anomaly associated with hydrocarbon contaminants in the vadose zone and ground water near the source area. The source of the geophysical anomaly was attributed to biogeochemical modifications of the contaminated zone by intrinsic bioremediation. During previous surveys, ground penetrating radar (GPR) data showed a zone of attenuated GPR reflections extending from the vadose zone to below the water table. Self potential (SP) data defined a positive anomaly coincident with the hydrochemically defined plume, while electrical resistivity data showed anomalously high conductivity within the zone of impact. In 2007, another integrated geophysical study was conducted at of the site. GPR, SP, electrical resistivity, and induced polarization survey were conducted with expectations of obtaining similar results as the past surveys. However, preliminary assessment of the data shows a marked decrease in groundwater electrical conductivity and SP response over the plume. GPR data showed the attenuated signals, but the zone of attenuation was only observed below the water table. We attributed the attenuation of the observed geophysical anomalies to ongoing soil vapor extraction initiated in 2003. Significant removal of the contaminant mass by the vapor extraction system has altered the subsurface biogeochemical conditions and these changes were reflected in the 2007 geophysical data. The results show that the biological and physical attenuation of the contaminant plume is detectable with geophysical methods