| Nanoparticles have grown in importance over the last decade with significant consumer and industrial applications. Yet, the behavior (fate and transport) of nanoparticles in the environment is virtually unknown. Research is needed to identify, characterize, and monitor nanomaterials in the subsurface. Here, we investigate the spectral induced polarization (SIP) response of nanometallic powders (nZVI, nAg, nTiO2, nZnO, and nCeO2) in porous geologic media. Our main objective is to determine the sensitivity of the SIP response (0.1-10,000 Hz) to the presence of nanoparticles (metals and metal oxides) in porous media. The SIP response was tested under various conditions: increasing particle concentration under constant solution chemistry; varying solution molarity (0.0M - 1.0M), and varying solution valence (+1, +2, +3 valence) under constant particle volume. We examine the results in terms of phase shift and resistance magnitude. Although surface area is a controlling factor for SIP response, our data suggest that the oxide nanoparticles do not show SIP responses to increasing particle concentration, solution valence, and molarity, while the metallic particles show a clear response to increasing particle concentration, and frequency. Silver was the only material to show any significant response to increasing solution molarity, valence, and frequency. Our results suggest that surface area may not be a dominant factor controlling the electrical response of nanoparticles in all cases; rather the mineralogy is an important consideration.;Additionally we investigate the spectral induced polarization (SIP) signature of hydrocarbon contaminated sediments undergoing soil vapor extraction (SVE) remediation. Previous geophysical studies have shown a clear geophysical anomaly over the contaminant plume. However, a SVE system installed over the site has since removed a significant amount of the hydrocarbon mass, resulting in a marked attenuation of the geophysical response observed from surface electrical geophysical methods. Field and laboratory scale SIP measurements were taken on sediments in order to assess the effect that contaminant removal has on SIP response and to characterize the SIP response from contaminated and uncontaminated sediments. Surface time domain IP profiles show increased real and imaginary conductivity and phase response from the upgradient location while the downgradient locations show little to no response compared to the background. Laboratory SIP measurements on contaminated sediment cores show increased phase and decreased real and imaginary conductivity response with increased hydrocarbon contamination. This work suggests that field and laboratory scale IP measurements are sensitive to the residual hydrocarbons in contaminated sediments and the physicochemical changes imparted on the sediments and that the SIP technique can play an important role in studies aimed at characterizing the extent of hydrocarbon contamination and remediation at contaminated sites. |
