Detailed leachate mapping using a 441 electrode full 3D setup using an extendable fishbone layout

3D surveying of resistivity and induced polarization has often utilized only a small number of electrodes determined by the number of addresses in the instrument. This is often in the range of 64-128 electrodes if mounted using a switching unit. Here we use a flexible and expandable 3D system that allows for arbitrary use of any set of parallel cables in a fish-bone structure. The measurements are performed at a large highly contaminated historic landfill in Denmark for a detailed mapping of the leachate plume migrating from the fill. A total of 441 stainless steel electrodes were installed along 7 lines (63 electrodes each). Each line was 410 meters long and the inter-line spacing is 25 meters making the total area 410 by 150 m. Six switch boxes enabled data acquisition with all 441 electrodes using a resistivity meter designed for only 64 electrodes. We collected data both in-line, and crossline to build a full 3D dataset consisting of several thousand 4- electrode measurements. The inversion identify a very conductive leachate plume migrating from the fill, with a fluid resistivity as low as 0.5 ohmm. Due to the dense 3D cover we identidfied a division of the main plume into two subplumes diverting as the distance to the landfill increses.