Surface Electrical Resistivity Research Articles

Hydrogeological, Hydrochemical, and Geophysical Analysis of a Brine-Contaminated Aquifer Addressing Non-Unique Interpretations of Vertical Electrical Sounding Curves

A comprehensive hydrogeological, geophysical, and hydrochemical investigation was conducted in southeastern Hitchcock County, Nebraska, within the Driftwood Creek alluvial aquifer. This study assessed groundwater contamination stemming from the surface disposal of saline wastes from oilfield activities. A contaminated area, initially identified through regional groundwater sampling, was examined in detail. Monitoring wells were installed, and groundwater and soil samples were collected for chemical analysis. Surface electrical resistivity surveys were also performed to delineate contamination patterns. The findings revealed that the groundwater contamination originated from the leaching of residual evaporative salts through the vadose zone, beneath an abandoned emergency-evaporation brine storage pit. Data from down-hole specific conductance logs, water quality analyses, and computer-generated interpretations of surface electrical resistivity indicated that contaminant migration was primarily influenced by gravity, bedrock topography, and the local hydraulic gradient. An initial surface electrical resistivity profile survey was conducted to optimize the placement of monitoring wells and soil sampling sites within the vadose zone. Following well installation, a contaminant source with complex brine contamination patterns was detected within the shallow aquifer. Vertical electrical soundings were then carried out as the final investigative step. The data from these soundings, combined with test hole records, water level measurements, brine contaminant distribution, and soil analyses, were refined through a computer program employing the method of steepest descent. By incorporating known layer thicknesses and resistivities as constraints, this approach minimized the common issue of non-unique electrical sounding interpretations, providing information on the distribution of brine contaminants within the alluvial aquifer.

Enhanced Cu-Cu bonding for ultrahigh-density interconnection: Co passivation bonding with non-oxidation interfaces

Cu-based hybrid bonding, known for its high density and low latency, is widely applied in big data throughput scenarios. However, Cu joints are prone to oxidation and perform poorly at fine pitches, hindering signal transmission and leading to failures in integrated devices. One of the most promising approaches to overcome these challenges is applying a cobalt (Co) passivation layer on the Cu surface owing to its preferable electrical and anti-electromigration behavior in sub-micron scale. However, the high melting point (∼1500 °C) and inevitable oxidation of the Co film coated on Cu are scarcely evitable. In this work, a ternary plasma composed of Ar, NH3, and H2O is introduced to activate the surface of the Co-passivated Cu, facilitating bonding at a temperature of 200 °C. Significant surface and interface electrical resistivity reductions were observed, reduced to 67.5 % and less than 10 %, respectively. Additionally, tensile strength more than doubled with ternary plasma activation attributed to the continuous and tightly bonded Co-Co interface. The application of this Co-passivated Cu bonding structure is evaluated through signal integrity simulations for 3D interconnection with ultrafine pitch. In summary, this work provides guidelines for the future fabrication of high-performance interconnection structures.

Polydopamine modified carbon fiber to improve the comprehensive properties of carbon paper for proton exchange membrane fuel cell

In this study, polydopamine (PDA) was used to modify functional groups on the surface of carbon fiber (CF), and the effects of different dopamine hydrochloride (DPH) concentrations on the surface morphology, functional groups, contact angle and dispersion stability of CF were studied. Subsequently, the raw carbon paper (RCP), hot-pressed carbon paper (HPCP) and carbon paper (CP) were prepared successively using the modified CF through wet forming, impregnation/hot-pressing, and carbonization methods. The surface morphology, tensile strength, flexural strength, electrical resistivity, air permeability and pore size distribution were analyzed for these materials. It was observed that the introduction of −OH and − NH2 groups improved the hydrophilicity and dispersion of PDA modified CFs, resulting in an increase in formation index (FI) from 39.2 to 48.1 for RCP samples. With increasing DPH concentration, the tensile strength of CP initially increased but then decreased while its electrical resistivity showed an opposite trend. Finally, PDA modified CP was assembled into proton exchange membrane fuel cells (PEMFC). The PEMFC assembled from DPH-CP-2.5 achieved a maximum limiting current density of 1440.0 mA/cm2 and power density of 458.25 mW/cm2. Meanwhile, the lower material transmission impedance for DPH-CP-2.5 as well as excellent water management ability and gas transmission performance.

Effect of boron doping levels on the piezoresistive properties of boron-doped diamond films prepared by HFCVD

The exceptional piezoresistive properties of boron-doped diamond (BDD) films render them highly promising for pressure sensor applications. These properties are closely associated with the doping concentration, crystal structure, and substrate material. In this study, BDD films with varying boron concentrations (B/C = 500–8000 ppm) were fabricated on silicon and diamond substrates using hot-filament chemical vapor deposition (HFCVD) equipment. The relationship between surface grain characteristics, grain boundaries, and gauge factor (GF) of BDD films deposited on different substrates was systematically examined. The concentration of boron doping significantly influenced the surface morphology, electrical resistivity, and GF of the BDD films. The grain size of BDD films initially increased as the boron doping concentration was raised from 500 ppm to 2000 ppm; however, it subsequently decreased when the boron doping content exceeded 2000 ppm. Moreover, we found that the piezoresistive impact of a BDD film is strongly correlated to its grain size; larger grain sizes result in higher GF values. Notably, compared to those on silicon substrates, the BDD films deposited on diamond substrates exhibited superior piezoresistive characteristics. Specifically at a doping concentration of 2000 ppm, a GF as high as 284 was achieved for the BDD film on a diamond substrate compared to only 140 for that on a silicon substrate.

Predictive analysis of electroconductive material parameters for system optimisation

This paper presents mathematical modelling based on predictive and correlation analysis of independent and dependent variables of conductive materials to develop sensors or actuators. The resulting analysis and optimisation develop improved systems based on sensors or actuators, including selecting the appropriate conductive materials for development. Toward this purpose, 46 materials with electroconductive properties were selected and analysed. The independent variables considered were mass, air permeability and thickness, and the dependent variable was defined as the electrical surface resistance of the conductive fabric used.

Advanced electro-assisted filtration of crude oil/water using a conductive mullite whiskers membrane

This study presents the development and characterization of a conductive composite membrane aimed at efficient oil-water separation via electrofiltration. The membrane comprises interconnected OH-functionalized multi-walled carbon nanotubes (OH-MWCNTs) and polyvinyl alcohol (PVA). Optimization parameters, including surface electrical resistance, water contact angle, and pure water permeance, were conducted, yielding an optimized membrane with a surface resistance of 256 Ω/sq, a contact angle of 39±2°, and a pure water permeance of 508.15 LMH/bar. The critical electric field intensity (Ecrit) was identified at 8–10 V, beyond which voltage increments had minimal flux impact. Electrofiltration experiments, incorporating filtration and backwashing, demonstrated enhanced permeate flux and oil particle removal rates under an applied electric field. Despite salt presence inducing flux reduction and fouling increase, membrane performance was still enhanced by the electric field. Energy consumption analysis revealed a 32 % reduction when combining electrical field with conventional filtration and backwashing, even at 1 mM concentration, compared to conventional filtration alone. This conductive composite membrane presents a promising, sustainable solution for effective crude oil/water separation across industries, offering improved performance, reduced fouling, and lower energy consumption.

Mapping and monitoring dense non-aqueous phase liquid source zone by fused surface and cross-borehole electrical resistivity tomography

Effective characterization of dense non-aqueous phase liquid (DNAPL) source zones is crucial for remediating polluted sites. DNAPL often reside as residuals or pools within high-permeability lenses and above impermeable layers due to soil heterogeneity, gravity, and capillary barriers. Given the high cost of drilling, electrical resistivity tomography (ERT) techniques—including surface ERT and cross-borehole ERT, are commonly used for DNAPL source zone mapping and monitoring. However, the low spatial resolution of ERT increases uncertainty in source zone investigations. This study proposes a method for improving DNAPL mapping and monitoring by fusing surface and cross-borehole ERT data. Sandbox experiments were conducted to simulate a heterogeneous DNAPL source zone, employing both ERT methods for static mapping and dynamic monitoring. Reflective light imaging (RLM) was used to visualize DNAPL migration and provide saturation data, allowing for the quantification of ERT's effectiveness in characterizing DNAPL distribution. The results indicate that individual ERT methods face significant challenges in DNAPL source zone mapping due to background interference. Surface ERT alone tends to underestimate the extent of deeper DNAPL source zones. However, fusing surface and cross-borehole ERT results in a complementary enhancement of vertical spatial resolution, thereby improving the characterization of DNAPL source zones. The fusion of static and time-lapse ERT data substantially enhances DNAPL source zone mapping and monitoring capabilities. By calculating the ratio of the ERT-monitored area to the actual area using resistivity change contours (5 %, 10 %, 15 %), it was found that fusing surface and cross-borehole ERT data improved monitoring resolution by 50.48 % compared to surface ERT alone and by 22.95 % compared to cross-borehole ERT. Principal component analysis (PCA) was effective in fusing time-lapse data, while the weighted average method (WAM) outperformed PCA for static resistivity data fusion.

Recuperação estrutural na Ponte da Torre

This article presents the main pathological manifestations identified in the Ponte da Torre (Tower Bridge), the destructive and non-destructive tests conducted for accurate diagnoses that confirm the structural compromise, as well as the methods adopted for the recovery of this Special Engineering Structure (OAE). Tests performed include core extraction, corrosion potential, surface electrical resistivity, carbonation, rebar scanning, chloride profile, and compressive strength testing. The Tower Bridge is a structure of high architectural and infrastructural importance for the city of Recife, serving the traffic demands of the northern zone of the capital of Pernambuco. Recognizing its significance, it is evident that preserving this OAE for future generations is necessary, incorporating principles of conservation, recovery, restoration, and more recently, sustainability. This study is part of the practice and execution of projects, interventions, and requalification efforts in the contemporary city, where the influence of the environmental aggressiveness class due to the surrounding environment is a fundamental factor for understanding the damage found in the bridge. Despite this, it was observed that one side of the structure shows more damage than the other, necessitating greater reinforcement on that side. The severe deterioration of the structure, especially of the concrete, in the Tower Bridge is directly related to the lack of regular inspections and corrective maintenance. Through this study, knowledge was gained regarding the procedures and methods that support and inform sustainable solutions adopted to ensure the safety and durability of the bridge.

An Integrated Hydration and Property Evaluation Model for Coral Powder–Cement Binary Blends

With the rise in the marine industry and marine tourism, coral powder is increasingly used to make concrete for marine islands. This study proposes a three-parameter hydration model and a hydration kinetic model to predict the performance of coral powder concrete based on previous experimental data. The process of the proposed prediction model is as follows: 1. The input parameters of the three-parameter hydration model are calibrated for the first 7 days using the cumulative hydration heat per gram of cement. The maximum cumulative hydration heat (455.87 J/g cement) and the shape coefficient (−0.87) remain constant. In this study, the hydration rate coefficients for 0%, 10%, and 20% coral powder were 6.91, 6.19, and 5.55, respectively, showing decreases of 10.41% and 19.68% compared with the specimens without coral powder. 2. At 28 days, the cumulative heat release values per gram of cement for 0%, 10%, and 20% coral powder were 389.77, 395.69, and 401.62 J/g, showing increases of 1.52% and 3.04% for the specimens containing 10% and 20% coral powder, respectively. Meanwhile, the hydration degrees for 0%, 10%, and 20% coral powder were 0.855, 0.868, and 0.881, respectively, showing increases of 1.52% and 3.04%. Furthermore, the cumulative heat release values per gram of binder were 389.77, 356.12, and 321.29 J/g, showing decreases of 8.63% and 17.56% for specimens containing 10% and 20% coral powder, respectively. 3. Properties such as compressive strength, ultrasonic pulse velocity (UPV), and surface electrical resistivity were evaluated using the power function and the cumulative hydration heat per gram of binder. 4. At 28 days, the chemically bound water contents for samples with 0%, 10%, and 20% coral powder were 0.2402, 0.2197, and 0.1981 g/g binder, respectively. Moreover, the calcium hydroxide contents were 0.1848, 0.1690, and 0.1524 g/g binder, showing reductions of 8.53% and 17.52% in bound water and 8.54% and 17.53% in calcium hydroxide. 5. A hydration kinetic model is proposed, which can distinguish between the dilution effect and the nucleation effect of coral powder, unlike the three-parameter model, which cannot distinguish between the two effects. Furthermore, the input parameters of the hydration kinetic model remain unchanged for different mixtures, while the input parameters of the three-parameter model must be varied among mixtures. Parameter analysis of the hydration kinetic model indicated that a low water–binder ratio and a high coral powder substitution rate significantly improve the relative reaction level of cement.

A Numerical Hydration Model to Predict the Macro and Micro Properties of Cement–Eggshell Powder Binary Blends

This study aims to propose a hydration kinetic model for the cement–eggshell powder binary system and predict the performance development of composite concrete through this model. The specific content and results of the model are as follows. First, based on the cumulative hydration heat of the cement and eggshell powder binary system in the first seven days, the parameters of the cement hydration model and the eggshell powder nucleation parameter are calibrated. These parameters remain constant regardless of the mix ratio. Secondly, the hydration heat of the cement–eggshell powder binary system over 28 days is calculated using the hydration model. The results show that at 28 days, for specimens with 0%, 7.5%, and 15% eggshell powder substitution, the cement hydration degrees are 0.832, 0.882, and 0.923, respectively. The hydration heat per gram of cement is 402.69, 426.88, and 446.73 J/g cement, respectively, while the hydration heat per gram of binder is 402.69, 394.86, and 379.72 J/g binder, respectively. Additionally, the hydration model is used to calculate the chemically bound water and calcium hydroxide content of the cement–eggshell powder binary system. At 28 days, for samples with 0%, 7.5%, and 15% eggshell powder, the chemically bound water content is 0.191, 0.188, and 0.180 g/g binder, respectively, and the calcium hydroxide content is 0.183, 0.179, and 0.173 g/g binder, respectively. Finally, a power function is used to regress the calculated hydration heat with experimentally measured compressive strength and surface electrical resistivity. The correlation coefficients for compressive strength and surface electrical resistivity are 0.8474 and 0.9714, respectively. This is because the strength weak point effect of eggshell powder has minimal impact on hydration heat and surface electrical resistivity experiments but significantly affects the strength experiment.

Effect of waste oyster shell powder on the micro- and macroproperties and sustainable performance of cement-based materials

A large amount of oyster shell waste is generated globally every year. Proper disposal of discarded oyster shells is crucial for reducing environmental pollution and achieving sustainable development. The aim of this paper was to study the feasibility of using waste oyster shells as a cementitious material to replace cement. The effects of waste oyster shell powder (OSP) with different water–binder ratios (w/b = 0.5, w/b = 0.2) and different substitution rates (10 %, 20 %) on the properties of cement-based materials were studied. The experimental results are as follows: The addition of oyster shell powder reduces the compressive strength, ultrasonic pulse velocity (UPV), surface electrical resistivity and cumulative heat of hydration of the mortar, but the strength loss is smaller for a water-to-binder ratio of 0.2 than for a water-to-binder ratio of 0.5. A good linear relationship between the compressive strength and UPV was also found. A good exponential relationship exists between the surface electrical resistivity and compressive strength. The heat of hydration results show that when the water–binder ratio is 0.5, replacing cement with waste OSP promotes aluminate phase hydration and advances the acceleration period. Finally, the carbon emissions of the mortar were normalized according to the compressive strength, and using OSP instead of cement at a low water–binder ratio was more conducive to reducing CO2 emissions.

Exploring enhanced high-temperature resistance: Analyzing the combined impact of fibers and nanoparticles in mortars

This study aims to explore the potential synergistic effect of polypropylene (PP) fiber and different types of nanoparticles to improve the high-temperature resistance of cementitious materials. For that, mortar samples with different PP fiber percentages, 0.6 wt% and 1.2 wt%, were produced. Different percentages of both colloidal nano-silica (CNS), 0.3 %, 0.6 %, and 0.9 %, and nano calcium carbonate (NCC), 0.5 %, 1 %, and 2 %, were used in the study. To test the resistance to elevated temperatures, mortar samples were exposed to different peak temperatures of 300°C, 600°C, and 900°C for 2 h, using unexposed samples as reference. Flexural and compressive strength, water absorption, surface electrical resistivity, and thermogravimetric analysis (TGA) of the heated and unheated samples were conducted. Results showed that, at 300°C heating regime, all samples with 0.6 % PP fiber exhibited an increase in flexural and compressive strength compared to their corresponding reference samples. For instance, specimens containing 0.6 % PP fiber and 2 % NCC content exhibited a 19 % increase in flexural strength compared to the unheated sample, whereas samples with 0.6 % PP fiber and 0.5 % NCC increased 32 % their compressive strength. In contrast, at 600°C, there was a major decline in mechanical properties in all samples, with samples containing NCC exhibiting the lowest amount (average of 61 % reduction in flexural strength and 32 % decrease in compressive strength). In general, a higher dosage of nanoparticles and lower PP fiber content will be better to resist temperatures up to 600 °C.

A Hydration-Based Integrated Model to Evaluate Properties Development and Sustainability of Oyster Shell Powder–Cement Binary Composites

Currently, oyster shell powder (OSP) is becoming more widely used in the production of cement-based materials. The purpose of this study is to propose a predictive model that can predict the properties of concrete materials incorporating oyster shell powder. The methods of this prediction model are given as follows. First, based on the measurement results of the heat of hydration in the first 7 days, the prediction parameters of the hydration model are obtained. Secondly, based on the hydration model, the measured results of the heat of hydration were extrapolated, and the heat of hydration from the start of stirring to day 28 was calculated. From the calculation results, the developments of compressive strength, ultrasonic velocity, and surface electrical resistivity were estimated. Finally, we evaluated the CO2 emissions of concrete incorporating oyster shell powder. The CO2 emissions corresponding to unit compressive strength and unit surface electrical resistivity were calculated. The important conclusions of the prediction model are given as follows. First, for different substitution amounts of oyster shell powder, the model result shows that the ultimate value of the heat of hydration corresponding to the unit cement mass is the same, i.e., 454.27 J/g. While the substitution amount of oyster shell powder increases from 0% to 30%, the model result shows that the cumulative 28-day hydration heat for 1 g cement increases the powder amount from 405.7 J/g to 419.3 J/g. Secondly, as the amount of substituted oyster shell powder increases from 0% to 30%, the model result shows that the cumulative 28-day heat of hydration per gram of cementitious material decreases this amount from 405.7 J/g to 293.4 J/g. Compressive strength, ultrasonic pulse velocity, and surface electrical resistivity can all be expressed as exponential functions of the heat of hydration. For compressive strength, ultrasonic pulse velocity, and surface electrical resistivity, the coefficients of determination for the simulation results and experimental results are 0.8396, 0.7195, and 0.9408, respectively. Finally, as the amount of substituted oyster shell powder increases from 0% to 30%, the model result shows that the CO2 emission per unit of compressive strength increases from 10.18 kg/MPa to 16.51 kg/MPa. As the amount increases from 0% to 30%, the model result shows that the CO2 emission corresponding to the unit surface electrical resistivity does not change significantly. In summary, the importance of this model is that it can predict various properties of concrete mixed with oyster shell powder, reduce the number of experiments, and promote the engineering application of oyster shell powder concrete.

Evaluation of Strain Sensors Based on Poly(acrylonitrile-co-butadiene) and Polypyrrole Synthesized by the Diffusion Method.

In this study, the functionality of an elastomer composite material containing polypyrrole (PPy) as a stress sensor was evaluated. The material was prepared using the swelling method by diffusing the pyrrole monomer into the elastomer before polymerization. To achieve adequate diffusion, organic solvents with affinity for the elastomer were used. The resulting materials were characterized by scanning electron microscopy (SEM), surface electrical resistance, and thermal and mechanical properties for application as a stress sensor. The simultaneous change in electrical resistance and tension stress was measured using a digital multimeter with electrodes connected to the jaws of a universal mechanical testing machine. The influence of stress cycles on the piezoresistivity of the composite materials was investigated. The obtained PPy/NBR composite presented a good combination of electrical conductivity and mechanical properties. The strain at break remained with mild variation after coating with PPy.

Cycle-to-cycle switching endurance variability in vertically aligned nanocrystalline molybdenum disulfide: computational insights

We propose a model to depict abrupt transient changes in the endurance test results of a resistive switching device comprising vertically oriented layers of nanocrystalline transition metal dichalcogenide layers with respect to the substrate. We aim to relate and understand the so-called resistance drift occurring in the endurance test results with our model, which is further tested using density functional theory simulations. We conclude that the relationship between resistance drift and skin effect is dominated by alternating electric current resistance and surface resistance. These results are crucial for understanding the resistance drift occurring in several resistive switching devices operating based on defects and ions.

Produce low-CO2 silica fume hybrid high-strength concrete using dry ice (solid CO2) as a CO2-utilized admixture

Concerns about high-strength concrete (HSC) have increasingly grown in tandem with the building industry's rapid development. However, the high CO2 emissions, high hydration heat, and high autogenous shrinkage of HSCs considered key issues that limit their wide application. In this study, various proportions of dry ice (solid CO2) were added to concrete to optimize HSC. The test results indicated that adding solid CO2 decreased the hydration heat and autogenous shrinkage and increased the mechanical properties and surface electrical resistivity of HSC. This is primarily attributed to the physical and chemical effects of solid CO2 in HSC curing. At 28 d of curing, the sample containing 3 wt% solid CO2 exhibited the most significant optimization effect. This is attributed to the fact that, at lower solid CO2 content (3%), the production of carbonation products compensates for the loss of strength caused by the reduction of hydration products. In addition, the addition of solid CO2 caused a decrease in the initial temperature, which delayed the hydration reaction and reduced the autogenous shrinkage. Adding solid CO2 led to an increase in acidity and promoted the formation of AFt, further reducing the autogenous shrinkage. And the more solid CO2 added, the greater the reduction in CO2 emissions for the mixture. Therefore, adding solid CO2 can play a role in optimizing the performance and promoting the sustainability of HSC and can contribute to the objectives of low CO2 emissions, low hydration heat, and low autogenous shrinkage of HSC.

Enhancing wearable humidity sensing with conductive PANi-Coated polyurethane nanofibers

This study presents a flexible nanofibrous humidity sensor for wearable applications and smart textiles. The methodology involved fabricating polyurethane (PU) nanofibers via electrospinning, followed by polyaniline (PANi) coating under varied synthesis conditions. Scanning electron microscopy (SEM) analysis revealed consistent diameter uniformity in the prepared PU nanofibers. Moreover, an increase in average nanofiber diameter (305 to 539 nm) was observed with rising polymer solution concentration (7% to 9%). Fourier-transform infrared spectroscopy (FT-IR) confirmed the physical presence of PANi on PU nanofiber surfaces without inducing structural changes. Additionally, the strength of PU nanofibrous samples, with or without PANi coating, increased proportionally with higher PANi and PU polymer concentrations. Electrical conductivity was measured using a four-point device, and surface resistance was assessed across varying humidity levels to study humidity’s impact on samples. Results exhibited a linear relationship between surface electrical resistance and relative humidity changes. Furthermore, the PU and PU/PANi nanofibers exhibit contact angles of 113° and 133°, respectively. The PANi-coated sample is more hydrophobic compared to the uncoated sample. In conclusion, these findings underscore the potential of the developed sensor as a responsive tool for monitoring humidity fluctuations in diverse applications.

Harnessing ion resource recovery: Design of selective cation exchange membranes via a synergistic ionic control method

Effective recovery of valuable ion resources such as lithium is gaining increasing importance. Monovalent selective cation exchange membranes (MCEM) used in electrodialysis have shown great potential, but their development is hampered by the classical trade-offs related to membrane permeability, selectivity and energy efficiency. We reported a new route to design high performance MCEM, utilizing the synergy of ionic control (IC) through cation-π bonding of polydopamine (PDA) and alternating current (AC), which has not been reported before. A set of deliberately controlled membrane fabrication conditions were chosen, with different ionic control (i.e., no cation, K+, Li+) and with/without AC for systematic comparison. Combining with morphology & electrochemical measurements, the membrane with electro-assisted K+ control, i.e., PDAM-K+/AC, exhibited respective 72 % and 51 % higher Li+ and K+ transport rate, higher permselectivity of 9.54 (Li+/Mg2+) and 17.86 (K+/Mg2+), and 3.3-fold lower surface electrical resistance (SER) compared to other modified membranes (e.g., PDAM). Also, PDAM-K+/AC exhibited no sign of scaling, supported by its much increased limiting current density. The results supported the hypothesis of the synergistic effect between cation-π bonding and AC electro-deposition, which altered the polymerization dynamics and produced more ordered membrane structure. The control strategy showed a viable route to fabricate ion exchange membranes for imparting monovalent selectivity, reducing scaling and avoiding energy penalty.

Factorial experimental design based on multiple factors for sensors and actuators development

Factorial experimental design based on multiple factors for sensors and actuators development

Characterization of a Contaminated Site Using Hydro-Geophysical Methods: From Large-Scale ERT Surface Investigations to Detailed ERT and GPR Cross-Hole Monitoring

This work presents the results of an advanced geophysical characterization of a contaminated site, where a correct understanding of the dynamics in the unsaturated zone is fundamental to evaluate the effective management of the remediation strategies. Large-scale surface electrical resistivity tomography (ERT) was used to perform a preliminary assessment of the structure in a thick unsaturated zone and to detect the presence of a thin layer of clay supporting an overlying thin perched aquifer. Discontinuities in this clay layer have an enormous impact on the infiltration processes of both water and solutes, including contaminants. In the case here presented, the technical strategy is to interrupt the continuity of the clay layer upstream of the investigated site in order to prevent most of the subsurface water flow from reaching the contaminated area. Therefore, a deep trench was dug upstream of the site and, in order to evaluate the effectiveness of this approach in facilitating water infiltration into the underlying aquifer, a forced infiltration experiment was carried out and monitored using ERT and ground-penetrating radar (GPR) measurements in a cross-hole time-lapse configuration. The results of the forced infiltration experiment are presented here, with a particular emphasis on the contribution of hydro-geophysical methods to the general understanding of the subsurface water dynamics at this complex site.