GEOTECHNICAL AND MULTIPLE GEOPHYSICAL METHODS FOR MAPPING THE GEOMETRY, LEACHATE AND BIOGAS IN THE OLD WASTE DUMPS IN NORTHEAST BRAZIL

Multiple geophysical methods are efficient for mapping the geometry of old waste dumps, detection of illegally buried waste, identification of areas enriched in leachate and biogas in landfills and mapping of contaminated areas. In Brazil, landfills and dumping are the most used municipal solid waste disposal methods. However, the inadequate disposal of municipal solid waste (open dumps or non-sanitary landfills) is still widespread in medium and small cities causing visual impacts, air contamination, odors and gas emission, vectors of diseases and soil, surface water and groundwater pollution. In this study we describe the results of the Magnetometric and Electrical Resistivity Tomography (ERT) investigation carried out in the largest dumping of construction and demolition waste installed in a former quarry in Northeast Brazil. The preliminary investigations of geotechnical survey in the upper portion of the waste massif indicated the occurrence of methane gas and the possible leachate at depth as well as the presence of concrete blocks with iron rebars and even other metals in smaller proportions. The modeling of resistivity and magnetic data was used as a tool to delineate volumes containing metal, which would correspond to low electrical resistivity values and high magnetic susceptibility. On the other hand, high resistivity measurements and low magnetic susceptibility were found to be associated with gas or compacted and unsaturated terrain. It was possible to confirm the geophysical anomalies with the presence of portions rich in organic matter with high humidity inside the dump, the presence of methane, concrete blocks, and ferrous material from the demolition of the construction industry, resulting from deep environmental drilling services and excavation of the waste dump for the implementation of subway station works.