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In many cities,urban development has reached the fringes of old industrial and mixed industrial/residential areas,where numerous brownfields are located.These urban brownfields usually present interesting and profitable occasions of urban land redevelopment.However,their environmental assessment is difficult due to their very large physical and chemical heterogeneity resulting from their anthropogenic origin (i.e.random filling of various municipal,industrial and demolition solid wastes).These highly heterogeneous fills,which may arguably be considered as anthropogenic soils,are very difficult to characterize using conventional drilling and sampling method because of their short spatial correlation in contaminant concentration and physical characteristics.This results in a significant uncertainty on the cost estimation for their management and remediation.This uncertainty slows down the overall effort in urban redevelopment,which results in important loss of public benefit.In Canada,this loss is estimated at 7G$ annually (National Round Table on the Environment and the Economy,2003).Therefore,the control of this uncertainty during environmental assessment is a key factor in facilitating the remediation of urban brownfields.A first step in controlling this uncertainty is through a more detailed (i.e.continuous) characterization of the physical heterogeneity of the fill in order to improve sampling plans,the representativeness of hydrogeological modeling and the efficiency of remedial actions.Accordingly,the objective of this study was to assess the potential of geophysical methods in providing a continuous characterization of the physical heterogeneity of a contaminated urban fill (1600 m2) in downtown Montreal (Canada).To this end,a geophysical approach based on the use of complementary methods was employed.Four methods were identified,namely:electromagnetic induction,magnetic gradiometry,electric tomography,and ground penetrating radar.The cross-interpretation of the results and a documented excavation of the fill (3200 m2) will make it possible to confirm the presence and the nature of heterogeneities.Part of the results is shown in the next figures.From these results,it is possible to differentiate certain distinctive zones of localized heterogeneity.According to the geophysical response,for instance in apparent electrical conductivity or resistivity,anomalies can be related to existing structures (e.g.concrete walls,underground tanks) and layers of different composition.The depth of the fill (i.e.the interface between the anthropogenic and natural soils) was estimated at a depth of 2 meters from the results of electrical resistivity and geological radar.The excavation of the fill is planned for spring 2007.A detailed stratigraphic description,sampling and analysis of metals and PAHs will be conducted in order to validate the geophysical anomalies.