In reply to Paul's request for further comments (see below)
I agree that it sounds a little disconcerting putting electrical stuff next
to VOCs. So, let me attempt to clarify a little. Certainly with
standard DC resistivity measurements, electrical currents and
current densities are very low (a few milliamps). These can be
higher in spectral IP surveys though the current itself will not lead to
significant heating. Similarly with electromagnetics and ground
probing radar, excitation energies in the ground tend to be relatively
small (though I know a similar argument has been used for their use
in UXO detection and the possibility of causing explosions. Anyone
who knows the outcome of that discussion may wish to comment,
but I understand the chances are minimal and certainly geophysical
detection of UXO continues).
The only possibility of explosion comes from sparks during
connection of any equipment to battery terminals or the use of
generators as a power source. Having worked on petroleum refinery
and chemical sites I am aware that the use of a "hot-works permit" or
a permit for works identifies the hazards and assesses the risks
associated with such works. Generators can have inhibitors
connected to them to reduce sparking and batteries can be
connected in "clean" areas in extreme cases. If there is serious
concern of explosive levels of vapour arising from spills on the
ground, then these should be taken into account prior to arrival on
site and be written into any site risk assessment. All site operatives
should then be provided with appropriate protection from
inhalation/exposure/explosion (e.g. masks, gloves, LEL meter or FID
to monitor levels etc).....
I have not heard of any examples of geophysically induced
explosions/fires and trust that that will remain the case! (I'm now
hoping not to receive a flood of responses detailing examples!!)
I hope this is helpful.
Best regards
Steve
On 4 Mar 2002 at 13:11, Paul McCombie wrote:
> Steve,
>
> A good reply, but seriously, is there not a safety issue here?
> Depending on what exactly was spilt, zapping the sort of high
> alternating current conventionally used for electrical resistivity
> surveys through ground contaminated with possibly volatile and easily
> ignited hydrocarbons would seem a little dodgy, to say the least? If
> more information should be given about this, such as the use of
> special equipment, or particular hydrocarbons that should not be
> investigated in this way, then I think that is important information
> that should be sent to the goup to follow what you have said already.
> Sorry to be asking this of you, but I think this matters.
>
> Paul.
>
> > -----Original Message-----
> > From: Geotechnical Engineering Email List
> > [mailto:[log in to unmask]]On Behalf Of SB Taylor
> > Sent: 04 March 2002 12:45 To: [log in to unmask]
> > Subject: Re: Electrical resistivity for oil contamination
> >
> >
> > 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
> >
>
Steve Taylor
School of Earth Sciences
University of Birmingham
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