Spectral induced polarization for the characterization of free-phase hydrocarbon contamination of sediments with low clay content: Near Surface
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| Title: | Main Title: Spectral induced polarization for the characterization of free-phase hydrocarbon contamination of sediments with low clay content: Near Surface |
| Description: | Abstract: The identification of organic pollutants in the soil and the subsurface is a goal of primary importance in the management of contaminated sites. However, only a few non-invasive techniques can be useful towards this goal. One such technique is spectral induced polarization. In this study, we investigate the spectral induced polarization effect of changing fluid saturation in a well-characterized porous medium, analysing the difference between air and hydrocarbons, at different degrees of water saturation. The experiments were conducted on fine eolic sand samples coming from an experimental site near Turin, Italy. Octanol and benzene were used as non-aqueous phase liquids. Samples were initially saturated with water having controlled electrical conductivity and subsequently de-saturated stepwise with injection of air at known pressure. The eolic sand samples were then re-saturated with the same water contaminated with hydrocarbons and then a non-aqueous phase liquid phase (either octanol or benzene) was injected in volumetric steps, in order to compare the effects of air and non-aqueous phase liquid invasion. At each saturation step, spectral induced polarization measurements were conducted in the 0.01 Hz to 1 kHz range using the ZEL-SIP04 impedance meter developed at the Forschungszentrum Juelich. The measurement setup guaranteed a 1 mrad phase precision for the entire frequency measurement range. Measurements were conducted under temperature controlled conditions at 20 (±0.5)° C. All spectral induced polarization curves show a peak in the range 0.01–1 Hz that changes in intensity and frequency with varying saturation and a high-frequency phase shift increase dominated by capacitive coupling effects of the measuring system. A multiple Cole-Cole model was fitted to the data. The effects of de-saturation on the low-frequency Cole-Cole parameters are that a) resistivity increases with decreasing water saturation but increases less with non-aqueous phase liquid than with the same volume of air; b) chargeability increases with decreasing water saturation but in presence of non-aqueous phase liquids its value is sometimes lower, sometimes higher and sometimes similar to the one observed in presence of air; c) the time constant τ increases with decreasing water saturation and is consistently larger with non-aqueous phase liquid than with air. These differences between air and non-aqueous phase liquid injection can be explained in terms of differences in non-aqueous phase distribution within the porous medium, as observed by X-ray micro-CT: while air is homogeneously distributed, non-aqueous phase liquids segregate under density effects. In summary, all spectral induced polarization effects of air and non-aqueous phase liquid injection in the considered porous medium are volumetric, i.e., are not due to interaction with grain surfaces or other electrical-chemical effects but are caused by pore obstruction by the electrically non-conductive phase. |
| Identifier: | 10.3997/1873-0604.2009028 (DOI) |
Responsible Party
| Creators: | Giorgio Cassiani (Author), Andreas Kemna (Author), Alberto Villa (Author), Egon Zimmermann (Author) |
| Publisher: | European Association of Geoscientists & Engineers |
| Publication Year: | 2013 |
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File Details
| Filename: | 2009_Cassiani_NSG.pdf |
| Data Type: | Text - Article |
| Size: | 16 Pages |
| File Size: | 2.1 MB |
| Date: | Accepted: 01.05.2009 |
| Mime Type: | application/pdf |
| Data Format: | |
| Language: | English |
| Status: | Completed |
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| Download Permission: | Only Project Members |
| General Access and Use Conditions: | For internal use only |
| Access Limitations: | For internal use only |
| Licence: | [TR32DB] Data policy agreement |
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Specific Information - Publication
| Publication Status: | Published |
| Review Status: | Peer reviewed |
| Publication Type: | Article |
| Article Type: | Journal |
| Source: | Near Surface Geophysics |
| Source Website: | www.nsg.eage.org |
| Volume: | 7 |
| Number of Pages: | 16 (547 - 562) |
Metadata Details
| Metadata Creator: | Johann Alexander (Sander) Huisman |
| Metadata Created: | 02.12.2013 |
| Metadata Last Updated: | 02.12.2013 |
| Subproject: | A3 |
| Funding Phase: | 1 |
| Metadata Language: | English |
| Metadata Version: | V50 |
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| Page Visits: | 859 |
| Metadata Downloads: | 0 |
| Dataset Downloads: | 1 |
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