Efficacy of an In‐Well Sonde to Determine Magnetic Susceptibility of Aquifer Sediment

Abstract

Magnetite is a natural component of many aquifers. Abiotic degradation of chlorinated solvents by magnetite can be an important mechanism for natural attenuation of these contaminants. The quantity of magnetite in aquifer materials can be estimated by measuring the magnetic susceptibility of the materials. This is most commonly done by determining the magnetic susceptibility of core samples in an analytical laboratory using a magnetic susceptibility meter. Unfortunately, the cost of acquiring core samples often makes an evaluation of abiotic degradation by magnetite economically unrealistic. Downhole sondes (probes) are available for the determination of magnetic susceptibility. In this study, a downhole sonde was evaluated as an affordable alternative to acquiring and analyzing core samples. The sonde was introduced into 10 monitoring wells. The data from the sonde were then compared to data from core samples that were collected from the same elevation as the sonde data. The core samples analyzed in the laboratory were used as the standard against which the sonde data were compared. The downhole sonde reported values that were similar to values reported on core samples. At most wells, the means of the two measurements could not be distinguished at the 95% confidence interval. When the means could be distinguished, they still agreed within a factor of two.

Quantification of TCE Co‐Oxidation in Groundwater Using a 14C–Assay

“…Groundwater samples were collected from five sites known to have TCE contamination: the former Twin Cities Army Ammunition Plant (TCAAP) in Shoreview, Minnesota; the former Plattsburgh Air Force Base (AFB) in Plattsburgh, New York; the former Hopewell Precision facility in Hopewell Junction, New York; the Tooele Army Depot near Tooele, Utah; and Hill AFB near Ogden, Utah. Additional site information and characterization is available in Wiedemeier et al (, ). Details on TCE concentrations and the presence of other volatile organic compounds (VOCs) at the sites are presented in Appendix S1, Supporting Information.…”

Reduction of PCE and TCE by magnetite revisited

“…Acetylene is a preferred end-product because it is benign and avoids the dichloroethene and vinyl chloride stall that commonly occurs with biotic reductive dechlorination pathways. [20][21][22][23][24] Of the Fe(II)-containing minerals, magnetite (Fe 3 O 4 ), a common mixed-valent Fe mineral, has been suggested to be responsible for chlorinated ethene attenuation at some field sites [24][25][26] despite slow rates of reduction by magnetite observed in laboratory experiments. 24,[27][28][29] Indeed, the promise of magnetite as a reductant for chlorinated ethenes has recently led some to suggest that high magnetic susceptibility of aquifer sediments could be used as a potential indicator for abiotic natural attenuation at a site.…”

“…24,[27][28][29] Indeed, the promise of magnetite as a reductant for chlorinated ethenes has recently led some to suggest that high magnetic susceptibility of aquifer sediments could be used as a potential indicator for abiotic natural attenuation at a site. 25 Such proxy methods are desirable due to the difficulty in measuring biologically labile products such as acetylene. We also note that more recent evidence alternatively implicates an oxidative abiotic pathway 30,31 based on a Fenton-like process involving OH radical in chlorinated ethene degradation by pyrite (FeS 2 ) in the presence of oxygen.…”

New Tools for Assessing Reactive Mineral‐Mediated Abiotic Contaminant Transformation

“…Depending on the site‐specific depositional environment and geochemistry, magnetite may be more relevant for abiotic degradation potential at some sites than iron sulfides. Wiedemeier et al () demonstrate the usefulness of a downhole sonde for measuring magnetic susceptibility in situ (without the need to collect core samples) and report a correlation between field‐scale chlorinated ethene degradation rates and magnetic susceptibility. However, it should be noted that magnetic susceptibility is a nonspecific and the presence of other iron minerals, like maghemite (which is not highly reactive with chlorinated solvents), may influence measurements.…”