Spectral induced polarization signatures of smoldering remediation enhanced with colloidal activated carbon: An experimental study

Monitoring the remediation of soil and groundwater contaminated by organic compounds remains highly challenging. Thermal treatments, such as smoldering combustion, have become established remediation techniques for destroying contaminants. Smoldering combustion can now be supported by colloidal activated carbon (CAC), with CAC being able to both adsorb contaminants and supplement the fuel source for destroying them. Despite this potential, effective performance monitoring of smoldering remediation remains limited. The objective of this study is to investigate the potential of the spectral induced polarization (SIP) geoelectrical technique to assess the performance of smoldering remediation of soils supplemented with CAC. SIP column experiments were first conducted to assess the response of SIP (i.e., real and imaginary components of the complex electrical conductivity) to varying concentrations of CAC in imitated field soils that contain, or do not contain, organic matter (OM). Results demonstrate that increasing OM and CAC contents increase both the real and imaginary conductivities, with the imaginary conductivity also showing frequency dependence. Smoldering and SIP column experiments were then conducted to assess the effectiveness of SIP for detecting changes in soils of varying OM and CAC contents that have been remediated by smoldering. Examination of the soils before and after smoldering indicates that SIP can track the evolving real conductivity and imaginary conductivity (in particular) between different soil compositions and different stages of the remedial process. High resolution scanning electron microscopy imaging was performed on all samples to validate the SIP and smoldering experiments, confirming significant reductions in carbon after smoldering. Overall, this study suggests that SIP has potential to track changes associated with the addition of remedial fluids like CAC in the subsurface, and the destruction of contaminants adsorbed to CAC by smoldering combustion.