The Potential Use of Residual Soil from Ribeira Valley (Brazil) in Mitigating Metal Contamination: A Geotechnical Characterization Jéssica Pelinsom Marques , Valéria Guimarães Silvestre Rodrigues , Orencio Monje Vilar , and Edmundo Rogério Esquivel Abstract The incorrect disposal of hazardous waste causes serious problems around the world. For instance, mining waste is one of the main sources of potentially toxic metals in the environment. In the Ribeira Valley region of Brazil, residues generated during lead ore smelting were improp- erly deposited in the Ribeira de Iguape River and on the soil’s surface without protection. An alternative solution for mitigating local contamination is verifying whether a local residual soil is appropriate to use as a mining waste landfill liner. The soil is sandy silty clay, with a plasticity index of 24%, an optimum water content, w opt , of 26.3% and a maximum dry density, q dmax , of 1.515 g/cm 3 from the Standard Proctor test. Specimens molded at an optimum compaction condition showed hydraulic con- ductivity of 10 -9 m/s and effective shear strength param- eters of c′ = 22 kPa and u′ = 26.8°. The soil is acidic (pH 4.6), exhibits low CEC (41.4 mmol c /dm 3 ) and presents a predominance of negative charges on the particle surface (PZSE 3.6 < pH), favoring cation retention. The hydrau- lic and mechanical characteristics together with the chemical properties suggest that this soil is a candidate for use as a liner. Further studies are underway to characterize its chemical contaminant retention and to complete the analysis about its suitability for the desired purpose. Keywords Tropical soil Á Liner Á Metal contamination 1 Introduction Inadequate disposal of hazardous waste causes serious problems around the world. Substances present in such waste can be released into the environment and affect its quality. For instance, potentially toxic metals can be absorbed by and accumulate in various lifeforms and persist for decades in the environment (Lester 1987; Alloway 1995). Potentially toxic metals originate in natural or anthropic processes, and their toxic effects depend on the quantity of the ions available for cation exchange (Sparks 1995; Sposito 1984). One of the main sources of metals in the environment is the incorrect disposal of mining waste that contains these elements. In the Ribeira Valley of Brazil, residues generated during the lead (Pb) ore smelting process were improperly deposited in the Ribeira de Iguape River. Between 1991 and 1995, waste was deposited directly onto the soil surface without base or cover protection. Thus, the river and soil were contaminated by metals such as Pb and cadmium (Cd) (Kasemodel et al. 2016). An alternative to minimize mining waste contamination is the deposition of residues in a waste containment facility with liner and cover systems. A liner ’s function is water- proofing and contaminant retention (Daniel 1993; Rowe et al. 1995). Besides low hydraulic conductivity and ade- quate shear strength, the material selected for the construc- tion of a sealant barrier must have favorable characteristics to retain the contaminants, and resistance to chemical ele- ments and to the erosive process (Bradl 2004). In the context of the Ribeira Valley problem, an alternative is the use of local soil as a liner. It’s a residual soil formed under tropical climate, for which there is still little information related to its contaminant retention ability. Thus, the purpose of the cur- rent study is to characterize a residual soil collected in the Ribeira Valley, to verify whether it presents suitable prop- erties to be used as a sealant barrier in mining waste con- tainment facilities. J. P. Marques (&) Á V. G. S. Rodrigues Á O. M. Vilar Á E. R. Esquivel São Carlos School of Engineering, University of São Paulo, São Carlos, SP 13566-590, Brazil e-mail: jessica.pelinsom.marques@usp.br V. G. S. Rodrigues e-mail: valguima@usp.br © Springer Nature Switzerland AG 2019 A. Shakoor and K. Cato (eds.), IAEG/AEG Annual Meeting Proceedings, San Francisco, California, 2018—Volume 2, https://doi.org/10.1007/978-3-319-93127-2_5 27