A Self-Potential for Monitoring Self-Sustaining Treatment for Active Remediation (STAR)
Self-sustaining Treatment for Active Remediation (STAR) is a novel soil remediation approach for Non-Aqueous Phase liquids (NAPLs) embedded in a porous medium. STAR is based on liquid smoldering combustion which destroys NAPLs while simultaneously generating heat due to the exothermic oxidation reaction. The technique is currently in use in several field pilot tests and a full-scale site remediation. Propagation of the smoldering front is monitored in the field by temperature data obtained from a thermocouple network, with limited resolution. Geophysical techniques, such as Self-Potential (SP), have potential as a non-destructive means for monitoring remediation processes. The SP method measures natural currents flowing in the ground generated by thermoelectric or electrokinetic processes. The objective of this work is to evaluate the potential of the SP technique for monitoring STAR. First, a series of sandbox experiments were conducted to investigate the magnitude of thermoelectric coupling coefficient for different sand sizes, water content and non- star heat sources. Results showed that a negative voltage anomaly is expected at the surface in the presence of a subsurface heat source and the magnitude of the anomaly is sensitive to water content and grain size. Next, SP measurements were conducted during several laboratory STAR tests examining the response as a function of both space and time. A significant SP anomaly was observed during the smoldering period. Moreover, the magnitude of the SP anomaly measured on the surface was demonstrated to be a function of the separation distance between the reaction front and the SP electrode position. R-squared for a linear regression of measured SP and the distance was 0.83, indicating that the majority of voltage anomaly had contribution to distance of the electrode to the smoldering front. Overall, this research demonstrated that the SP technique has significant potential as a non-invasive monitoring tool for STAR.
site remediation, smoldering, STAR, non-aqueous phase liquids, monitoring, self-potential
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