M. Schmutz

Changes in induced polarization associated with the sorption of sodium, lead, and zinc on silica sands

Low-frequency dielectric spectroscopy can be measured in terms of a conductance and a phase lag between the electrical current and the electrical field. This conductance and phase lag can be written as into a complex conductivity with both an in-phase and quadrature components that are frequency dependent. In sands, the low-frequency (10 mHz-40 kHz) spectra of the complex conductivity are dominated by the polarization of the electrical double layer (especially the internal part of the electrical double layer called the Stern layer) and the Maxwell-Wagner polarization (typically above 100 Hz). We present a polarization that is able to explain the complex conductivity spectra including the grain size distribution, the porosity, and the complexation of the mineral surface with the ions of the pore water. To test this model, we investigate the sorption of various cations (Na, Pb, Zn) characterized by different affinities with the surface of silica. Sand column experiments were carried out to see the change in the complex conductivity during the advective/dispersive transport of a lead nitrate solution and a zinc sulfate solution, replacing a sodium chloride solution in the pore space of the sand. The complex conductivity model is able to explain the change of the phase over time.

Least squares inversion of self‐potential (SP) data and application to the shallow flow of ground water in sinkholes

We propose a least squares inversion algorithm to determine the spatially variable depth of the water table in shallow unconfined aquifers using self-potential signals measured on the ground surface. Traditionally, the water table is determined only at few locations using piezometers. Our approach relates its shape with the distribution of the self-potential signals according to a Fredholm equation of the first kind. The latter is discretized to obtain a linear matrix formulation of the forward problem. This new formulation is very general and can account for the resistivity distribution of the vadose zone. It is used to setup the inverse problem using the approach of Tarantola (1987) for a test site located in Normandy (France) where 225 self-potential measurements were performed over an area of 15,400 m2. Ground water flows through the loess overlying a low permeability clay-with-flint weathered chalk, at a depth between 1 to 7 meters, into sinkholes in chalk bedrock. The method determines the water table with a precision of 0.4 m.

A physical model of the low‐frequency electrical polarization of clay rocks

Low-frequency (0.18 Hz to 1.5 kHz) effective dielectric spectra have been measured on a set of near-saturated samples of argillite. The measured spectra of the real part of the complex apparent permittivity did not show significant correlation with cation exchange capacity (CEC) per unit mass of rock values. They satisfied a power law relationship with the frequency, at least for samples with CEC values lower than 10 cmol/kg. The Maxwell-Wagner-Hanai-Bruggeman formulation used for a two-phase mixture has been modified to account for mutual polarization between the pockets of water located in the micropores and those located in the macropores. The results of the modeling calculations illustrate (1) the ability of this new formulation to reproduce the power law relationships of the measured spectra of the real and imaginary components of the complex permittivity and (2) the strong impact of the pore electrical conductivity.

Spectral Induced Polarization Detects Cracks and Distinguishes between Open- and Clay-filled Fractures

Spectral induced polarisation (SIP) is applied to the detection and localization of fractures located in the roof of an abandoned quarry at Saint-Germain-la-Rivie`re (Gironde, southwest France). Two types of fracture are observed in the roof of the galleries: open (mostly clay-free) and clay-filled. The phase between current and voltage is used to detect the presence of these fractures and can differentiate those with or without clays. The amplitude and phase of complex conductivity can be analysed using a Cole-Cole model of relaxation times. Open fractures are characterized by very low chargeability and a high relaxation time in the order of 3 ms. Clay-filled fractures are characterized by high chargeability and a low relaxation time.

Apport de l'association des méthodes TDEM (Time-Domain Electromagnetism) et électrique pour la connaissance de la structure du glissement-coulée de Super Sauze (bassin de Barcelonnette, Alpes-de-Haute-Provence, France)

The aim of this study is to determine an investigation protocol that permits the Super Sauze flowslide to be described along continuous lines, through the association of electrical and TDEM (Time-Domain Electromagnetism) methods. The transition from one resistivity range to another often corresponds to the three layer limits defined by geotechnical soundings. The results presented show that the combined methods are well suited to the question investigated and that they are validated by the geotechnical data.

Integrated Investigations on Landslides — The Example of the Super Sauze Earthflow

In the southern French Alps in general, and particularly in the Barcelonnette basin, the landslides are frequent in the Callovo-Oxfordian marls. The Super Sauze landslide is an interesting example of the complex landslides that occurred in clays or marls, with flows following a slide, flow taken in accordance with the terminology defined in Landslide recognition, edited by the International Association of Geomorphologists (Publication no. 5, Report no. 1 of the European Commission Environment Programme, Contract No. EV5V-CT94-0 454). It seemed to us essential to complete the data used in the various tests, calculations and models carried out on similar landslides in the basin by several authors, in view of a more accurate prevision of the hazard.

The Relative Importance of Saturated Silica Sand Interfacial and Pore Fluid Geochemistry on the Spectral Induced Polarization Response

Author(s): Peruzzo, L; Schmutz, M; Franceschi, M; Wu, Y; Hubbard, SS | Abstract: ©2018. American Geophysical Union. All Rights Reserved. Adsorption at the solid-pore fluid interface is a key mechanism controlling the mobility of nutrients and contaminants in subsurface soils and sediments. The spectral induced polarization (SIP) method has been shown to be sensitive to the quantity and type of adsorbed ions. Extending previous results, we investigated the relevance of pH, solution conductivity, and ion type on the SIP response of saturated silica sand. We also performed adsorption experiments to evaluate whether adsorption plays a relevant role on the effect of saturating solution conductivity and pH. Given their environmental relevance and different electrochemical characteristics, we focused on exploring the influence of Cu2+ and Na+ adsorption on the SIP signature. The adsorption results confirm the expected and modeled pH influence on the adsorption of both Cu2+ and Na+. The measured quadrature conductivity spectra indicate that pH and solution conductivity control the electrical double layer electrochemical state and its capacitive behavior. On the contrary, no appreciable SIP signal changes are associated with ion substitution. The adsorption experiments highlight low values of site occupancy for Na and Cu, which suggests that the effects of pH and fluid conductivity are unrelated to their control on the ion adsorption. We interpret the solution conductivity as a proxy for ionic strength. The relative importance of pH and solution conductivity over ion type helps to further constrain the interpretation of SIP results in field geochemical and biogeochemical characterization and monitoring.

Characterizing Stream-Aquifer Exchanges with Self-Potential Measurements

Characterizing the interactions between streams and aquifers is a major challenge in hydrology. Electrical self-potential (SP) is sensitive to groundwater flow through the electrokinetic effect, which is proportional to Darcy velocity. SP surveys have been extensively used for the characterization of seepage flow in a variety of contexts. But to our knowledge, a model coupling SP and groundwater flow has never been implemented for the study of stream-aquifer interactions. To address the issue, we first implemented a two-dimensional model to a synthetic stream-aquifer cross section. Results underline the very distinct nature of SP profiles in gaining or losing stream conditions. Second, we presented a field application in a transect crossing a stream in losing conditions. The coupled model successfully reproduced the observed SP profile. This inverse modeling of the SP signal provides quantitative data on hydrodynamic parameters (hydraulic conductivity, hydraulic heads) and geophysical parameters (coupling coefficient). Nevertheless, all relevant parameters cannot be uniquely estimated without precise prior information on at least some of these parameters. Our results confirm the potential of SP surveys on the characterization of stream-aquifer exchanges. Recommendations on the collection of high-quality data are also provided, along with a description of the contexts in which the methodology is likely to perform well.