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| Titel |
Monitoring of organic contaminants in sediments using low field proton nuclear magnetic resonance |
| VerfasserIn |
Chi Zhang, Yuri Rupert |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125693
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| Publikation (Nr.) |
 EGU/EGU2016-5309.pdf |
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| Zusammenfassung |
| The effective monitoring of soils and groundwater contaminated with organic compounds is
an important goal of many environmental restoration efforts. Recent geophysical methods
such as electrical resistivity, complex conductivity, and ground penetrating radar have been
successfully applied to characterize organic contaminants in the subsurface and to monitor
remediation process both in laboratory and in field. Low field proton nuclear magnetic
resonance (NMR) is a geophysical tool sensitive to the molecular-scale physical and chemical
environment of hydrogen-bearing fluids in geological materials and shows promise as a novel
method for monitoring contaminant remediation. This laboratory research focuses
on measurements on synthetic samples to determine the sensitivity of NMR to
the presence of organic contaminants and improve understanding of relationships
between NMR observables, hydrological properties of the sediments, and amount and
state of contaminants in porous media. Toluene, a light non-aqueous phase liquid
(LNAPL) has been selected as a representative organic contaminant. Three types
of porous media (pure silica sands, montmorillonite clay, and various sand-clay
mixtures with different sand/clay ratios) were prepared as synthetic sediments. NMR
relaxation time (T2) and diffusion-relaxation (D − T2) correlation measurements were
performed in each sediment saturated with water and toluene mixed fluid at assorted
concentrations (0% toluene and 100% water, 1% toluene and 99% water, 5% toluene and
95% water, 25% toluene and 75% water, and 100% toluene and 0% water) to 1)
understand the effect of different porous media on the NMR responses in each fluid
mixture, 2) investigate the role of clay content on T2 relaxation of each fluid, 3)
quantify the amount hydrocarbons in the presence of water in each sediment, and
4) resolve hydrocarbons from water in D − T2 map. Relationships between the
compositions of porous media, hydrocarbon concentration, and hydraulic properties of
sediments will be presented and discussed. A minimum toluene detection limit has been
established, and influences on NMR signals from increasing contaminant concentration
have been investigated as well. It is evident in our data that the dominant control of
porous media on NMR responses relies on clay content in the sand-clay mixture. |
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