In the Netherlands there are many polluted sites that contain the highly toxic Dense Non-Aqueous Phase Liquids (DNAPL). Pure DNAPL's penetrate through sand and often accumulate on less permeable layers in the subsurface. Locating pure DNAPL product is often a bottle-neck for the successful remediation of these sites Various methods for the localisation of DNAPL's have been tried in recent years. All these methods have, up to now, hardly been applied after their trials due to high costs and/or the long duration of these methods. For this reason a project started (January 2002, see acknowledgements) to demonstrate the applicability of Electrical Resistivity Tomography (ERT) to locate pure DNAPL's in the Dutch situation. ERT is a geophysical technique that has been applied to detect or monitor electrical resistivity contrasts between boreholes (e.g. Newmark et.al. 1998). DNAPL's have a very high electrical resistivity (e.g. Schneider and Greenhouse 1992). A problem with applying ERT is that the definition of the 'best' measurement schedule (a list of four-electrode configurations to be addressed by the resistivity meter) remains a poorly resolved problem (Labreque quoted in Slater et.al. 2000). The project consists of three phases: 1) selecting promising electrode configurations on the basis of a literature study and modelling, 2) demonstrating ERT at a site with a shallow (~5 m below the surface) pollution, 3) demonstrating ERT at a site with a deep (~20 m below the surface) pollution. This paper presents some of the results from the modelling and the field measurements at the first site.


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