Geoelectrical imaging and cluster analysis for leachate mapping in a municipal solid waste landfill: A case study in...

Landfill stability and environmental protection are critical issues in municipal solid waste (MSW) management, especially in tropical countries, where warm and humid conditions can accelerate leachate and gas production. This paper investigated a landfill in Brazil that operated for 24 years (1993-2016), with over 30 % of the MSW consisting of organic matter. Electrical resistivity tomography (ERT) and time-domain induced polarization (IP) surveys were performed along two survey lines for mapping leachate distribution. The results were analyzed using unsupervised machine learning, visualization tools, and descriptive statistics in the R programming language. Standard penetration tests (SPT) were conducted to validate cluster analysis. A comparison of ERT and IP profiles obtained 20 years apart suggested significant leachate presence and varying degradation rates within the waste body, even years after waste disposal activities had ceased. Geoelectrical data were grouped into seven clusters, which were interpreted based on material type (soil and MSW), degree of saturation (partially and fully saturated waste), and organic matter content (from dry to biogeochemically active zones). The SPT tests confirmed complex fluid distribution by revealing leachate ejection and gas emissions at specific regions of the landfill showing low resistivity (below 10 Ωm) and moderate to high chargeability (from 5 to 60 mV/V) and normalized chargeability (from 1 to 7 mS/m). The findings demonstrated the effectiveness of geophysical imaging techniques for site monitoring and highlighted the potential for energy recovery from old MSW.