G.

By oil I will assume LNAPLs e.g (BTEX type petroleum products)
though this is applicable to others hydrocarbons as well.

The expected electrical response is somewhat confusing if you read
through the literature but for good reasons.  Laboratory and carefully
constructed field trials almost always indicate that the result of a
petroleum-type spill leads to an increase in the resistivity.  However,
these laboratory trials tend to be short time-scale and hence there is
no time for  biodegradation of the oil.  (Also they may use "clean"
sands which will not ideally promote the process).  The process of
biodegradation leads to a build up of related acids in the soil which is
coincident (or near to) the oil - mostly bacteria tend not to like the
stuff neat, prefer the dissolved phase.  This and actually increases
the conductivity of the pore fluid producing a decrease in resistivity.
This tends to be an aerobic process, so needs to take place in an
oxygen rich environment.

Geophysical methods used to detect hydrocarbon spills include
electromagnetic, resistivity, Spectral IP (which we are researching
here at the University of Birmingham, UK) and GPR, which has been
shown to be successful under the right conditions in mapping
hydrocarbon contamination.  I also have a very nice example of an
old (30 year) hydrocarbon spill mapped using electromagnetic
techniques - so yes Paul, someone has!

Finally, for reference go to:
http://www.eegs.org/eegssvr/details88_0299.asp?numero=59
this is the abstract to a paper on the subject:
Sauck, W.A., Atekwana, E.A., and Nash, M.S., 1998, High
conductivities associated with an LNAPL plume imaged by integrated
geophysical techniques: Journal of Environmental and Engineering
Geophysics, 2, p. 203-212.
Also try Atekwana, E.A., W.A. Sauck, and D. Werkema, 2000,
"Investigations of Geoelectrical Signatures at a Hydrocarbon
Contaminated
Site"; Journal of Applied Geophysics, Vol. 44, No. 2-3, pp.
167-180.
If you'd like more details, or would like to discuss this further
feel free to e-mail me directly
Best regards
Steve




On 4 Mar 2002 at 15:34, G. Habibagahi wrote:

> Dear all
> Has anyone experience with using electrical resistivity to detect
> petroleum contaminated ground (or groundwater)? Appreciate any hints
> or literature on the subject. regards
>
> G. Habibagahi
> Associate professor
> Dept. of Civil Engineering
> School of Engineering
> Shiraz University
> Shiraz - Iran
>

Dr Steve Taylor
Alta Geophysics Research Unit
Birmingham Research & Development Ltd
Research Park
Edgbaston
Birmingham
Bxx xxx
Tel : 0121 414 6134
Fax : 0121 414 4942