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| Titel |
Spectral induced polarization signature of contaminated soil |
| VerfasserIn |
N. Schwartz, J. A. Huisman, I. Shefer, A. Furman |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063461
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| Zusammenfassung |
| Spectral induced polarization (SIP) signatures of porous media contaminated with
non aqueous phase liquids (NAPL) were measured using an accurate impedance
meter. The samples were prepared by mixing air-dried sand with 15% by weight of
bentonite clay, tap water and either diesel fuel or motor oil. Next, the soil was packed
in a column and left for 24 hr before electrical measurements were performed.
For all the samples, water saturation was constant (Sw = 0.47) and the NAPL
saturation was 0 (control), 5, or 15 percent. Counter-intuitively, the results show that
addition of NAPL to the porous media resulted in an increase of the real part of the
complex conductivity. Evidently, for each type of contaminant, an increase in the
contaminant saturation resulted in an increase in the real part of the conductivity. The
imaginary part of the complex conductivity showed a reversed behavior: higher NAPL
saturation resulted in a reduction of the imaginary part of the complex conductivity.
For both the real and the imaginary part of the complex conductivity, the effect of
NAPL on the complex electrical conductivity was more significant for motor oil than
for diesel fuel. In addition to the electrical measurements, we also performed an
extraction experiment to examine the effect of the presence of NAPL on the electrical
conductivity (EC) of the pore water. The results from the extraction experiment
showed that addition of NAPL to the porous media resulted in an increase of the pore
water EC. We argue that this increase in the real part of the complex conductivity is
related to adsorption of organic polar compounds from the NAPL onto the mineral
surface and the associated release of inorganic ions from the mineral surface to the
pore water. These exchange processes affect both the surface and the pore water
conductivity. In addition, we suggest that the decrease in polarization (associated with the
imaginary part of the complex conductivity) of the NAPL contaminated porous media is
related to stronger binding of the adsorbed NAPL polar compounds to the mineral
surface. Ongoing experiments are targeted at further elucidating these phenomena. |
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