Electrical conductivity profiling for rapid contamination assessment in unsaturated zones: A case study of an MSW...

This study investigates the potential of using bulk soil electrical conductivity (EC_bulk) to predict pore water conductivity (EC_pw) for assessing the contamination in the unsaturated zone of an old municipal solid waste (MSW) landfill. EC_bulk, EC_pw, and water content were evaluated with depth at an old MSW landfill in Bhalswa, Delhi, using the Hydraulic Profiling Tool (HPT) and a dual tube soil sampling system. This data was also supplemented by a cone penetration test (CPTu) for high-resolution soil type identification. The correlation of EC_bulk with EC_pw was primarily influenced by volumetric water content and mineral conductivity with the latter being negligible at this site due to the high conductivity of the leachate. A reasonable linear correlation between normalized EC (EC_bulk/EC_pw) was observed with volumetric water content, except at low water contents. EC_bulk and EC_pw profiles with depth indicated attenuation of contaminants in clay layers, while sand layers exhibited constant profile with depth. EC_pw was contributed by macro ions generally found in the leachate, including Na⁺, Mg²⁺, K⁺, Ca²⁺, NH₄⁺, Cl^-, SO₄^2-, and HCO₃^-, as demonstrated by a strong correlation with their cumulative ionic strength. The results indicate that EC_bulk profile can be used as a rapid semi-quantitative method for assessing contaminant migration in the unsaturated soil zone, supporting the remediation or control strategies at old landfills.