Electrical resistivity as a tool for the recognition of a brownfield ; La résistivité électrique comme outil pour la reconnaissance d'une friche industrielle

Abstract

The industrial brownfield site of Montagne-du-Nord (France) is home to zinc metallurgy and lead and sulphuric acid manufacturing activities. Hydrological and geochemical studies were carried out in pits and boreholes after the site had been shaved and covered by backfilling. Geophysical data (slingram electromagnetic mapping, 2D and 3D electrical panel, and electrostatic dideshy) make it possible to locate ground and mineral water, to position interfaces between layers, to identify where water is released to river drains and to characterise the unsaturated area, with good spatial resolution. ; International audience The industrial waste land in Montagne-du-Nord (France) has been occupied by a zinc and a lead smelter unit linked to sulphuric acid production. Then this factory has been razed and covered by coarse waste deposits below sandy fillings. Hydrological and geochemical studies have been systematically carried out by drillings and pits following a mesh of 50m x 50m. This waste land constitutes an area where the metallic contamination is important. The physical property of subsoil materials, sensitive to this contamination, is the electrical resistivity; it depends on water mineralization and quantity presented in all formations. Geophysical data allow to locate precisely mineralized soil and water with higher spatial resolution. A complete geophysical study, using methods based on electrical resistivity (slingram electromagnetic mapping, 2D and 3D electrical imaging, and electrostatic logging) has been carried out. The slingram mapping allows to determine conductive anomalies coincident with chemical anomalies obtained into the piezometers, and to locate the water seepage toward the river drain. The electrical imaging allows to indicate precisely the location of clayey alluvial deposits, and to describe the superficial seepage areas. The electrostatic logging gives an accurate description of the not saturated area in boreholes, near anomalies located with the two other methods. Those geophysical ...