Vortragsreihe Ökologie und Umweltforschung WS 2017/18

Electrical imaging of subsurface nano- and micro-scale particle injections for in situ groundwater remediation

Application of nano and micro-scale particles has emerged as a promising in situ remediation technology for the remediation of contaminated groundwater, particularly for areas difficult to access by other remediation techniques. The performance of nanoparticle injections, as a foremost step within this technology, is usually assessed through the geochemical analysis of soil and groundwater samples. This approach is not well suited for a real-time monitoring, and often suffers from a poor spatio-temporal resolution and only provides information from areas close to the sampling points. The talk will present an alternative method to overcome such limitations based on the application of non-invasive Induced Polarization (IP) imaging, a geophysical method that provides information on the electrical properties of the subsurface.

The analysis of spatial and temporal changes in the electrical images allows tracking the propagation of the injected particles as well as to detect the induced bio-geochemical changes in the subsurface. Here, we present IP monitoring results for data collected at two different experiments: (i) during the injection of Nano-Goethite particles (NGP) used for simulation of biodegradation of a BTEX plume (i.e., benzene, toluene, ethylbenzene, and xylene); and  (ii) during the injection of microscale zero-valent iron (mZVI) to enhance chemical transformation of an aquifer impacted by chlorinated aliphatic hydrocarbons (CAHs). Pre-injection imaging results revealed high electrical conductivities; which might appear as contradictory observations considering that hydrocarbons are poor electrical conductor. Nevertheless, such response can be explained by the release of metabolic by-products accompanying the stimulation of microbial activity due to the presence of hydrocarbons in the subsurface. Moreover, background images of the induced polarization (IP) reveal contrasting signatures for the different pollutants. Such changes can be explained by variations in the pore-space geometry which are characteristic to given geochemical properties of the pollutants. Post-injection images revealed a significant change in (> 50%) the electrical conductivity and induced polarization images, with even larger changes in the proximity of the injection points. Temporal changes in the electrical images are consistent with variations in particles concentration reported in groundwater and soil samples, as well as geochemical parameters such as pH and oxidation-reduction potential. Our results demonstrate the applicability of IP imaging for the real-time monitoring of nano- and micro-scale particle injection, as well as of the accompanying geochemical changes.

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invited by Sven Frei, Hydrology

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