After an extensive desk study and a number of trial surveys, electrical and electromagnetic techniques were chosen for the geophysical investigation of 2 ex-oil distribution terminals in West Granton, Edinburgh, which the City of Edinburgh Council aim to acquire for remediation and redevelopment. An electromagnetic survey of the site was conducted, using a Geonics EM31 conductivity meter, as part of a complete assessment of the surface pollution. A 2-D resistivity survey was later employed to image the geology beneath the site with the aim of locating potential contaminant pathways. The EM31 is directionally dependent and yields different results when its boom is either parallel or perpendicular to subsurface linear anomalies. Use of the second derivative of unidirectional measurements clarified the response of a labyrinth of underground pipes easing interpretation by geophysicists and non-geophysicists alike. The electromagnetic survey also successfully located at number of shallow oil plumes emanating from the ends of buried, broken pipes. The computer controlled 2-D resistivity imaging method provided rapid coverage of the Granton site returning a large number of 2-D apparent resistivity pseudosections. The subsurface pipe network had a significant effect on the resistivity measurements and masked the response of the background geology. In order to reconstruct the background resistivity distribution, the effect of a subsurface linear conductor was quantified using a known analytical solution. Pipes could then be located and their effects removed from apparent resistivity pseudosections. Contour plots (plan views) of the background resistivity distributions across the complete site were then constructed by extracting true resistivity data points from all modelled profiles at equivalent depths. These contour plots proved invaluable for the assessment of the integrity of the superficial clay coverage, for the location of faults and for resolving complex geology. The conclusions obtained from non-invasive geophysical surveying over the Granton site far exceed any interpretations that could be drawn from an invasive survey alone. As a result of the work, the Granton site remediation plans have been substantially redesigned and the benefits of geophysics have been promoted.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663270 |
| Date | January 1999 |
| Creators | Vickery, Anna C. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14602 |
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