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

Abstract

This study investigates the potential of using bulk soil electrical conductivity (ECbulk) to predict pore water conductivity (ECpw) for assessing the contamination in the unsaturated zone of an old municipal solid waste (MSW) landfill. ECbulk, ECpw, 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 ECbulk with ECpw 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 (ECbulk/ECpw) was observed with volumetric water content, except at low water contents. ECbulk and ECpw profiles with depth indicated attenuation of contaminants in clay layers, while sand layers exhibited constant profile with depth. ECpw was contributed by macro ions generally found in the leachate, including Na+, Mg2+, K+, Ca2+, NH4+, Cl−, SO42−, and HCO3−, as demonstrated by a strong correlation with their cumulative ionic strength. The results indicate that ECbulk 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.