Integration of Electrical and Electromagnetic Investigation for Contaminated Site

Abstract

Problem statement: The environmental assessment of industrial areas is required to minimize the risk of soil and groundwater contamination. The survey of wide areas (e.g., some hectares) provides a high economical and complex logistical impact when random strategies of soil sampling are adopted. Recently, geophysical methods had been successfully adopted to drive the process of the spatial sampling of the soil. Approach: The main goal was to verify the reliability of the geophysics for the detection of buried wastes in an industrial area previously involved in the vehicle demolition. Two geophysical methods were applied (1) the electromagnetic frequency domain, using a multi-frequency broadband system with a fixed spacing between the transmitter and receiver coils (2 m) to observe the soil electrical conductivity and in-phase response (2) the electrical resistivity and chargeability tomographies, performed along several transects. We applied the Kriging method to map the conductivity and the in-phase response. Standard inversion procedure was adopted to interpret the resistivity and chargeability data. Results: We found a very similar response of the electromagnetic survey in range between 2000 and 40,000 Hz: The investigation depth (3-4 m) was mainly related to the coil spacing. The survey pointed out some anomalies caused by bio-geochemical activity in the active waste deposits. The resistivity and chargeability sections confirmed that the electromagnetic anomalies were related to the waste. The high chargeability values (up to 100 mV/V) were associated to the leakages of metals of the wastes. Conclusion: The electromagnetic survey, even if sensitive to the presence of cultural noise (fence, metallic object on the ground), permitted to detect the industrial waste; the electrical resistivity and chargeability data pointed out the main contaminated zones with good accuracy. The further development may focus on the relationship between the nature of waste and the geophysical response.