Evidence of Coupled Carbon and Iron Cycling at a Hydrocarbon-Contaminated Site from Time Lapse Magnetic Susceptibility


Conventional characterization and monitoring of hydrocarbon (HC) pollution is often expensive and time-consuming. Magnetic susceptibility (MS) has been proposed as an inexpensive, long-term monitoring proxy of the degradation of HC. We acquired repeated down hole MS logging data in boreholes at a HC-contaminated field research site in Bemidji, MN, USA. The MS data were analyzed in conjunction with redox conditions and iron availability within the source zone to better assess whether MS can serve as a proxy for monitoring HC contamination in unconsolidated sediments. The MS response at the site diminished during the sampling period, which was found to coincide with depletion of solid phase iron in the source zone. Previous geochemical observations and modeling at the site suggest that the most likely cause of the decrease in MS is the transformation of magnetite to siderite, coupled with the exhaustion of ferrihydrite. Although the temporal MS response at this site gives valuable field-scale evidence for changing conditions of iron cycling and stability of iron minerals it does not provide a simple proxy for long-term monitoring of biodegradation of hydrocarbons in the smear zone.


Geosciences and Geological and Petroleum Engineering


Chevron Energy Technology Company
National Crude Oil Spill Fate and National Attenuation Research Site


Chevron grant #CW852844

Keywords and Phrases

Biodegradation; Carbon; Hydrocarbons; Magnetic Susceptibility; Pollution Detection; Well Logging; Contaminated Sites; Field Research; Iron Availability; Iron Minerals; Long Term Monitoring; Redox Condition; Sampling Period; Unconsolidated Sediment; Iron; Dissolved Oxygen; Ferric Hydroxide; Ground Water; Hydrocarbon; Magnetite; Mineral; Siderite; Unclassified Drug; Carbon Cycle; Chemical Pollutant; Redox Conditions; Sampling; Sediment Pollution; Temporal Analysis; Transformation; Alkalinity; Article; Biogeochemical Cycling; Carbon Cycling; Controlled Study; Iron Cycling; Magnetism; Model; Oxidation Reduction Reaction; Plume; Pollution Monitoring; Water Contamination; Water Table; Bemidji; Minnesota; United States

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Article - Journal

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