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Ground Electromagnetic Survey (GEM-2) technique to map the hydrocarbon contaminant dispersion in the subsurface at Barry Docks, Wales, UK

Yaccup, Rahman and Brabham, Peter 2012. Ground Electromagnetic Survey (GEM-2) technique to map the hydrocarbon contaminant dispersion in the subsurface at Barry Docks, Wales, UK. Presented at: AWAM International Conference on Civil Engineering (AICCE12) and Geohazard Information Zonation (GIZ 12), Park Royal SPA, Penang, Malaysia, 28-30 August 2012.

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The Geophex GEM-2 electromagnetic (EM) instrument provides a rapid multifrequency technique for shallow geophysical exploration. Survey applications include; ground contamination, hydrogeology, groundwater contamination mapping and archaeological investigations. This highly portable hand-held instrument, when linked with active GPS tracking provides typical 1.5 ground point spacing and allows a surveyor to collect around 20,000 data points per hour over five frequencies. GEM-2 uses an active EM signal to detect variations in subsurface conductivity. EM currents result in a secondary magnetic field that is measured together with the original transmitted signal, using a receiver coil on the EM instrument. The depth of ground penetration attained is dependent on a number of factors, and the most significant is the ground conductivity and the chosen EM wave frequencies. Typically five wave frequencies are used in the surveys; 825Hz, 7075Hz, 16075Hz, 31025Hz and 40075Hz. This paper presented the results from the investigation at Barry Docks site undergoing redevelopment from a 50 year old oil terminal into future residential use. Typically, polluting contaminants will increase the electrical conductivity of the ground materials and ground water. However measured ground conductivity values actually depend upon the types of hydrocarbon present. Some pure hydrocarbons are electrically resistive but their conductivity values may also increase through time due to biodegradation over many years. This research programme carries out detailed GEM-2 surveys in conjunction with chemical sampling to investigate this conductivity and ground chemistry relationship on the first layer of the GEM-2 data. The study shows that the high conductivity zones correspond to the location of the hydrocarbon storage tanks, although there is a tank response showing no such signal.

Item Type: Conference or Workshop Item (Paper)
Date Type: Completion
Status: Unpublished
Schools: Earth and Environmental Sciences
Subjects: Q Science > Q Science (General)
Q Science > QE Geology
Uncontrolled Keywords: Electrical Conductivity, Hydrocarbon contamination, GEM-2 System, Barry Docks
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Last Modified: 04 Jun 2017 04:23

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