Complex-conductivity monitoring to delineate aquifer pore clogging during nanoparticles injection

Abstract

SUMMARYLaboratory and field studies have demonstrated the applicability of nanoparticles (NP) for accelerated contaminant degradation. Beside other limitations (e.g. costs, delivery, longevity, non-target specific reactions), concerns of regulators arose regarding toxicity of injected NP and particles delivered off-target (i.e. renegade particles). Renegade particles also significantly reduce the efficiency of the remediation. The delivery of particles off-target is caused, mainly, by unintended fracking, where the fractures act then as preferential flow paths changing the trajectory of the particles. Hence, the real-time monitoring of particle injection is of major importance to verify correct particle delivery and thus help to optimize the remediation strategy. However, to date NP monitoring techniques rely on the analysis of soil and water samples, which cannot provide information about clogging or the formation of fractures away of the sampling points. To overcome these limitations, in this study we investigate the applicability of complex-conductivity imaging (CCI), a geophysical electrical method, to characterize possible pore clogging and fracking during NP injections. We hypothesize that both processes are related to different electrical footprints, considering the loss of porosity during clogging and the accumulation of NP in areas away of the target after fracking. Here, we present CCI results for data collected before and during the injection of Nano-Goethite particles (NGP) applied to enhance biodegradation of a BTEX (benzene, toluene, ethylbenzene and xylene) contaminant plume. Imaging results for background data revealed consistency with the known lithology, while overall high electrical conductivity values and a negligible induced-polarization magnitude correspond with the expected response of a mature hydrocarbon plume. Monitoring images revealed a general increase (∼15 per cent) in the electrical conductivity due to the injected NGP suspension in agreement with geochemical data. Furthermore, abrupt changes in this trend, shortly before daylighting events, show the sensitivity of the method to pore clogging. Such interpretation is in line with the larger variations in CCI resolved in the unsaturated zone, clearly indicating the accumulation of renegade NGP close to the surface due to fracking. Our results demonstrate the applicability of the CCI method for the assessment of pore clogging accompanying particles injection.

Advancing hydrological process understanding from long‐term resistivity monitoring systems

“…Our review is research‐focused, but we note that opportunities exist for deployment of LTRM systems in the environmental consulting sector. One promising area is in monitoring environmental remediation processes to evaluate effectiveness of amendment delivery (Flores Orozco et al, 2019; LaBrecque, Miletto, et al, 1996; LaBrecque, Ramirez, et al, 1996) and its long‐term impact on subsurface biogeochemistry. Although not yet commercially available, the costs of low‐power LTRM systems, such as the system described in Figure 1, are significantly lower than conventional high‐power geophysical instruments on the market.…”

“…Our review is research-focused, but we note that opportunities exist for deployment of LTRM systems in the environmental consulting sector. One promising area is in monitoring environmental remediation processes to evaluate effectiveness of amendment delivery (Flores Orozco et al, 2019;LaBrecque, Miletto, et al, 1996; and its long-term impact on subsurface biogeochemistry.…”

Quantification of soil textural and hydraulic properties in a complex conductivity imaging framework: Results from the Wolfsegg slope

“…The IP method was developed for the prospection of metallic mineral ores given the strong IP response in the presence of iron sulphides (Pelton et al, 1978). In recent years, IP has emerged as a promising method for various environmental and hydrogeological applications including the mapping of geochemical active zones (Flores-Orozco et al, 2020;Katona et al, 2021), the monitoring of changes in pore-space geometry accompanying bioremediation processes (Flores Orozco et al, 2011;Flores Orozco et al, 2019) and the assessment of permafrost degradation (Doetsch et al, 2015;Maierhofer et al, 2022), just to name a few. In the context of characterizing hillslopes affected by landslides, IP has revealed promising results (Flores Orozco et al, 2018a;Gallistl et al, 2018;Revil et al, 2020), as numerous laboratory studies reported a sensitivity of the IP method to soil-textural properties of the subsurface (Slater and Glaser, 2003;Tarasov and Titov, 2007;Revil and Florsch, 2010) and, thus, the improved estimation of hydraulic conductivity (Slater et al, 2014;Weller et al, 2015;Weller and Slater, 2019).…”

Cross‐borehole geoelectrical time‐lapse monitoring of in situ chemical oxidation and permeability estimation through induced polarization

“…Commer et al ., 2011; Chen et al ., 2012; Orozco et al ., 2011, 2013) and monitoring chemical remediation through injection of micro to nanoscale iron (e.g. Slater and Binley, 2006a; Flores Orozco et al ., 2015 ; Flores Orozco et al ., 2019).…”