Giulliana Mondelli

Interpretation of Resistivity Piezocone Tests in a Contaminated Municipal Solid Waste Disposal Site

A resistivity piezocone (RCPTU–resistivity cone penetration test with pore pressure measurement) and groundwater and soil samplers were used to detect contamination from a landfill for urban solid waste located in the state of Sao Paulo in southeastern Brazil. Background resistivity values were obtained in the laboratory using undisturbed soil samples. The strong influence of clay minerals common in tropical soils made it difficult to interpret the tests and to differentiate potentially contaminated zones from changes in soil type. A local correlation between fines content and the soil behavior index (Ic) of the various collected soils allowed the RCPTU tests to be interpreted to identify the contaminated regions of the aquifer. These results showed excellent repeatability and allowed for a detailed stratigraphic analysis of the highly heterogeneous profiles. Electrical resistivity measurements have proven to be an interesting resource to help detect contaminated soils, thus improving the quality and efficiency of geoenvironmental site investigations using integrated direct and indirect techniques. The interpretation of resistivity piezocone tests for the study site is not straightforward as it is in sedimentary sands since soil genesis affects soil behavior and soil and water sampling is required to support interpretation.

Geo-Environmental Site Investigation for Municipal Solid Waste Disposal Sites

Deactivated dump sites and inadequate sanitary landfills can be a serious potential source of contamination. Due to the large number of these sites, contaminants can be generated and migrate into the ground. For this reason, site investigation programs which consider different types of soils and contaminants are needed. In many countries, sanitary landfills have been recently built according to the engineering standards with satisfactory procedures and following the requirements imposed by the local environmental agencies, including monitoring and proper operations. There is a great concern with the operation of sanitary landfills and with the future of deactivated dump sites located in small and medium-size cities, since many of them were inappropriately constructed and operated. Consequently, the main surficial streams and groundwater aquifers, subsoil and air become vulnerable to contamination and pollution. A continuous site investigation program, including in-situ and laboratory tests are necessary to identify the typical soil profile, hydrogeological characteristics and background chemical values. The site surroundings and the subsoil contamination plume can be characterized based on geotechnical, geochemical and mineralogical techniques.