Iron Mineral Transformations At A Hydrocarbon Contaminated Long-Term Research Site Inferred From Magnetic Susceptibility
Abstract
Iron Mineral Transformations At A Hydrocarbon Contaminated Long-Term Research Site Inferred From Magnetic Susceptibility
Yokus1, S., Ntarlagiannis1, D., Isaacson2, C., Rios-Sanchez2, M., Cozzarelli3, I., Bekins4, B., Atekwana5, E., Torrance2 , A., Rapp2, E. and Slater1, L. Department of Earth and Environmental Sciences, Rutgers University Newark, Newark, NJ Center for Sustainability Studies, Bemidji State University, Bemidji, MN Water Mission Area, ESPD, United States Geological Survey, Reston, VA. Water Mission Area HQ, United States Geological Survey, Menlo Park, CA College of Earth, Ocean and Environment, University of Delaware, Newark, DE Long-term monitoring of biogeochemical transformations of hydrocarbon contaminants in the subsurface is important for assessing the vulnerability of groundwater resources and habitats impacted by them. Geophysical measurements have the potential to improve understanding of the transformation of iron minerals at hydrocarbon-contaminated sites. At a long-term research site over an oil spill near Bemidji, MN, magnetite transformation to siderite has been postulated to explain long term decreases in magnetic susceptibility (MS) signals in boreholes. To further investigate this hypothesis, magnetic susceptibility measurements were taken in the laboratory on artificial sands containing small percentages of magnetite, siderite, and ferrous iron-coated sand. Iron mineral particle size and concentration were varied. Magnetic susceptibility measurements were also acquired on new cores acquired from the field for comparison against measurements from 2011, 2013 and 2015. Finally, mineral packages (sands containing magnetite and hydrous ferrous oxyhydroxide (HFO) minerals) were suspended in the smear zone and periodically retrieved over a 12-month period to assess the MS changes over time. The laboratory measurements confirm the large decrease in MS between magnetite- and siderite-containing samples and constrain the sensitivity of the MS measurement to volume concentration changes in magnetite and siderite at this site. Time-lapse measurements on the mineral packets installed in the wells show a progressive decrease in MS over time in both the magnetite and HFO containing packets. In addition, borehole logging confirmed that high MS signals observed in the smear zone in 2011, reduced in 2013 and absent in 2015, remain absent eight years later. These findings all support the argument that transformation of magnetite to siderite, coupled to exhaustion of ferrihydrite, is occurring at this hydrocarbon contaminated site and can be monitored with magnetic susceptibility.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B53F2459Y
- Keywords:
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- 0406 Astrobiology and extraterrestrial materials;
- BIOGEOSCIENCES;
- 0418 Bioremediation;
- BIOGEOSCIENCES;
- 1505 Biogenic magnetic minerals;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1835 Hydrogeophysics;
- HYDROLOGY