Optimum model in 2D geoelectrical imaging : example from a dump site with high resistivity contrasts

Modelling and inversion of synthethic data over 2D geologie models have shown that, at high resistivity contrasts, there could be an increase in the model misfit between the inverted model and the true model for successive iterations. Hence, the optimum model is attained at a low iteration number. A case history, from data measured over a waste dump site, is given in which the optimum model is the structure at the second iteration; the inverted resistivities are very low at less than 30 Om down to a depth of about 10 m. These are consistent with the analyses of surface - and ground - water which indicate the presence of a low resistivity contaminant.