Characterization of transport processes in a heterogeneous aquifer using electrical resistivity tomography (ERT)

Tracer experiments were carried out for the characterization of the spatial and temporal variability of transport processes in heterogeneous aquifers. At the Krauthausen test site (Germany) two large scale tracer experiments were conducted to investigate the potentiality of electrical resistivity tomography (ERT) for imaging subsurface transport. First, a CaCl(2) tracer solution with a higher electrical conductivity (EC) than the groundwater was injected. One year later, the same experiment was repeated using a "negative" tracer with a smaller conductivity than the groundwater. With ERT, changes in bulk electrical conductivity of the aquifer were monitored, and translated to groundwater EC using calibration relations that were determined in laboratory measurements on aquifer sediments. The salt tracer showed a density driven drift to the middle and lower parts of the aquifer while the "negative" tracer moved primarily through the upper and middle parts. The comparison between ERT and local breakthrough curves derived from multilevel groundwater sampling showed that resistivity tomograms are an appropriate surrogate for traditional concentration maps.