Self‐potential for monitoring soil remediation by smouldering: a proof of concept

Near‐surface soils contaminated with non‐aqueous phase liquids, such as coal tar, crude oil, and chlorinated solvents, remain a serious problem. Smouldering remediation is a technique now being applied in the field for in situ destruction of non‐aqueous phase liquids. Based on a self‐sustaining exothermic reaction, smouldering remediation generates a hot region (>400 °C) that propagates through the subsurface. Self‐potential is here considered for the first time as a non‐destructive means for monitoring the smouldering remediation process. First, a series of sandbox experiments were conducted to investigate the magnitude of the thermoelectric coupling coefficient ( C TE) for different sand sizes, water contents, and heat sources. MeasuredC TEvalues ranged from ‐0.47 mV/°C for coarse, water‐saturated sand to ‐0.05 mV/°C for fine sand with a saturation of 30%. Next, self‐potential measurements were conducted during several laboratory smouldering remediation experiments, examining the response as a function of both space and time. A significant self‐potential anomaly was observed on the surface during the smouldering period. Moreover, the magnitude of the self‐potential anomaly was demonstrated to be highly correlated to the separation distance between the (moving) reaction front and the (stationary) self‐potential electrode positions. Overall, this research suggests that the self‐potential method has a significant promise as a non‐invasive monitoring tool for in situ smouldering remediation of contaminated sites.