Characterization and monitoring of subsurface contamination from Olive Oil Mills' waste waters using Electrical Resistivity Tomography

Evaluating the reliability of geophysical methods for investigating the migration of a hydrocarbon plume: Validation by sample analysis

Geophysical methods are extensively used to assess contaminated sites. However, the validation of geophysical exploration results remains crucial for practical applications of these methods. In this study, Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) were used to investigate an abandoned hydrocarbon-contaminated site in Jiangsu, China. Dense survey lines were drawn across the contaminated site to generate continuous monitoring data. In addition, 20 boreholes were strategically drilled at identified anomalous points using geophysical methods. Multiple groundwater samples were analyzed from these boreholes and analyzed hydrocarbon concentrations. The obtained geophysical data were compared with groundwater data to assess the hydrocarbon extent and degree at the study site, as well as to evaluate the reliability of the geophysical survey results. The results demonstrated the effectiveness of continuous resistivity profiles in mapping the contaminant plume, showing consistent contaminant migration directions with the groundwater flow. The contaminant plume patterns obtained by interpolating groundwater sample contaminant concentrations were in line with the resistivity profiles. Groundwater samples from boreholes in high-resistivity zones exhibited higher hydrocarbon concentrations than corresponding regulatory limits. On the other hand, GPR successfully identified enhanced reflective signals associated with the presence of hydrocarbons, necessitating comprehensive interpretations that integrate these findings with resistivity results. The analysis results of unsatisfactory geophysical data in relation to the specific site conditions indicated that soil layer heterogeneity was the main source of anomalous electrical responses. This study validated the accuracy and efficiency of geophysical methods in investigating the migration of hydrocarbon plumes and assessing their contamination levels in groundwater.

Groundwater electro-bioremediation via diffuse electro-conductive zones: A critical review

Microbial electrochemical technologies (MET) can remove a variety of organic and inorganic pollutants from contaminated groundwater. However, despite significant laboratory-scale successes over the past decade, field-scale applications remain limited. We hypothesize that enhancing the electrochemical conductivity of the soil surrounding electrodes could be a groundbreaking and cost-effective alternative to deploying numerous high-surface-area electrodes in short distances. This could be achieved by injecting environmentally safe iron- or carbon-based conductive (nano)particles into the aquifer. Upon transport and deposition onto soil grains, these particles create an electrically conductive zone that can be exploited to control and fine-tune the delivery of electron donors or acceptors over large distances, thereby driving the process more efficiently. Beyond extending the radius of influence of electrodes, these diffuse electro-conductive zones (DECZ) could also promote the development of syntrophic anaerobic communities that degrade contaminants via direct interspecies electron transfer (DIET). In this review, we present the state-of-the-art in applying conductive materials for MET and DIET-based applications. We also provide a comprehensive overview of the physicochemical properties of candidate electrochemically conductive materials and related injection strategies suitable for field-scale implementation. Finally, we illustrate and critically discuss current and prospective electrochemical and geophysical methods for measuring soil electronic conductivity-both in the laboratory and in the field-before and after injection practices, which are crucial for determining the extent of DECZ. This review article provides critical information for a robust design and in situ implementation of groundwater electro-bioremediation processes.

Identification of dense nonaqueous phase liquid sources in groundwater: a review of isotope technique

Excessive dense nonaqueous phase liquids (DNAPLs) in subsurface aquifers posed a threat to human health and sustainable development of groundwater resources. Accurately identifying the sources of DNAPLs is crucial for groundwater remediation and prevention efforts. In the previous studies, significant advances were made in using isotope techniques for identifying DNAPLs in groundwater. In this paper, we provide a comprehensive overview of the commonly used isotopic tools applied to source identification. This overview will outline the advantages and limitations of the isotope technique and describe the needs for future research. Isotope tracing techniques are based on the unique isotopic characteristics of DNAPLs from different sources, enabling the identification and differentiation of DNAPL sources. The δ13C and δ37Cl values are most commonly used for identifying DNAPLs in groundwater. In field applications, however, the differences in isotopic characteristics from diverse sources can be weakened after undergoing a series of human and natural factors, which can affect the accuracy of source identification. To improve the accuracy of DNAPL source identification, a dual-isotope tracing approach seems the best available solution. Nonetheless, in the face of complex polluted environments, the dual-isotope method seems stretched. Therefore, further researches remain to be carried out to accurately and efficiently assess the sources of DNAPLs in groundwater and their individual contributions. This is a prerequisite for groundwater resource conservation and remediation efforts.

Typology and classification of water quality in an intermittent river in a semi-arid Mediterranean climate

The typology and classification of rivers are highly relevant concepts in the field of limnology and freshwater ecology. Water body typology systematically categorizes water bodies based on their natural attributes, while water body classification groups them based on specific criteria or purposes for management, regulatory, or administrative reasons. Both concepts play important roles in understanding and managing water resources effectively. This scientific article focuses on the ZAT River in Morocco as a model for studying low-flow and intermittent rivers. The objective is to develop an accurate model for the typology and classification of small, low-flow rivers into homogeneous classes based on natural and anthropogenic factors. The study also investigates the impact of human activities on altering the uniformity and reference nature of the water body. The typology of water bodies is carried out according to the European methodology specified in The European Commission's Water Framework Directive (WFD) in 2000. The classification of water bodies is conducted by assessing their chemical and biological quality using the weighted index (WI), the Iberian Biological Monitoring Working Group (IBMWP) index, and multivariate statistical methods such as principal component analysis (PCA) for confirming water quality assessment. The results indicate the possibility of dividing the basin into four water bodies. Water bodies show homogeneity in terms of chemical quality when human influence is minimal or during periods of high river flow. However, increased human influence and decreased river flows lead to heterogeneity in chemical quality, indicating an unstable state. This study is the first of its kind in arid and semi-arid intermittent rivers, where such an approach could be suggested to determine their typology and classification.

Controlled-Release Materials for Remediation of Trichloroethylene Contamination in Groundwater

Groundwater contamination by trichloroethylene (TCE) presents a pressing environmental challenge with far-reaching consequences. Traditional remediation methods have shown limitations in effectively addressing TCE contamination. This study reviews the limitations of conventional remediation techniques and investigates the application of oxidant-based controlled-release materials, including encapsulated, loaded, and gel-based potassium permanganate since the year 2000. Additionally, it examines reductant controlled-release materials and electron donor-release materials such as tetrabutyl orthosilicate (TBOS) and polyhydroxybutyrate (PHB). The findings suggest that controlled-release materials offer a promising avenue for enhancing TCE degradation and promoting groundwater restoration. This study concludes by highlighting the future research directions and the potential of controlled-release materials in addressing TCE contamination challenges.

Integrated environmental characterization and assessment of an exposed historic manure repository

Historic manure stockpiled (active from 1935 through 2018) in a repository mound approximately 15 m high with a 31,415.93 m² footprint was sampled from various depths at six locations in an environmental assessment framework. The manure samples were analyzed for nutrient content to investigate potential application as a soil amendment to local fields in combination with biowaste disposal regulations. Results indicate that manure can be used as a soil amendment; however, different crops and land conditions require specific nutrients, and application must be determined accordingly. Likewise, the manure analysis did not indicate any negative issues that would disallow land application as a disposal option. In addition to limiting environmental soil boring into the manure repository, two-dimensional geophysical electrical resistivity imaging was performed to characterize and quantify the deposited manure. Based on those efforts, the material volume within the site's manure repository was calculated to be 611,942.354 cubic meters (m³). Finally, based on the geophysical results and the historical information about the manure's deposited volume in the study area, an estimation of the released landfill gases and its expected produced energy is presented.

A Review on Applications of Time-Lapse Electrical Resistivity Tomography Over the Last 30 Years : Perspectives for Mining Waste Monitoring

Mining operations generate large amounts of wastes which are usually stored into large-scale storage facilities which pose major environmental concerns and must be properly monitored to manage the risk of catastrophic failures and also to control the generation of contaminated mine drainage. In this context, non-invasive monitoring techniques such as time-lapse electrical resistivity tomography (TL-ERT) are promising since they provide large-scale subsurface information that complements surface observations (walkover, aerial photogrammetry or remote sensing) and traditional monitoring tools, which often sample a tiny proportion of the mining waste storage facilities. The purposes of this review are as follows: (i) to understand the current state of research on TL-ERT for various applications; (ii) to create a reference library for future research on TL-ERT and geoelectrical monitoring mining waste; and (iii) to identify promising areas of development and future research needs on this issue according to our experience. This review describes the theoretical basis of geoelectrical monitoring and provides an overview of TL-ERT applications and developments over the last 30 years from a database of over 650 case studies, not limited to mining operations (e.g., landslide, permafrost). In particular, the review focuses on the applications of ERT for mining waste characterization and monitoring and a database of 150 case studies is used to identify promising applications for long-term autonomous geoelectrical monitoring of the geotechnical and geochemical stability of mining wastes. Potential challenges that could emerge from a broader adoption of TL-ERT monitoring for mining wastes are discussed. The review also considers recent advances in instrumentation, data acquisition, processing and interpretation for long-term monitoring and draws future research perspectives and promising avenues which could help improve the design and accuracy of future geoelectric monitoring programs in mining wastes.

Delimiting Pig Slurry Affected Subsurface Areas by Combining Geophysical and Geochemical Techniques

In Spain, livestock farming is a significant activity area that generates substantial revenues and essential jobs. However, the actual impact that this intensive activity might have on the environment is not entirely understood. Moreover, coastal aquifers are subjected to a significant environmental pressure due to nearby growing population, intensive agriculture, and livestock farming. In this work, three representative pig slurry ponds, under semiarid conditions, were studied using different techniques to evaluate the subsurface conditions in terms of pH, electrical conductivity, salts, and nitrate content. The electrical resistivity tomography (ERT) technique was employed in this study, which provides electrical resistivity values from the subsurface materials and fluids. These electrical resistivity values were compared to data obtained from geochemical analyses to derive their relationships and establish the pig slurry-affected subsurface area. Thus, ERT-based lower electrical resistivity values were associated with higher salts concentrations and nitrate content. ERT values indicated a near-surface affected by slurry infiltration that coincided with the increase of geochemical values obtained from sample analyses. Additionally, Spearman’s correlation was used to evaluate the correlation between electrical resistivity data and the physical-chemical properties of soil. The most important pollutant accumulation mainly occurs in the two-meter depth. Therefore, the risk of slurry ponds affecting deep aquifers is limited in the studied area. Finally, this study proves a complete, affordable, and scalable methodology application to livestock residue storage facilities.

Estimation Parameters of Soil Solute Transport Processes by Using the Electric Resistivity Method

Preferential solute transport is a common phenomenon in soil, and it is of great significance to accurately describe the mechanism of pollutant transport and water and soil environmental governance. However, the description of preferential solutes still relies on applying solute breakthrough curves for model parameters fitting. At present, most of the solute breakthrough curves are obtained indoors, and with some limitations. Therefore, this study established a method for securing solute breakthrough curves based on the electrical resistivity method. The research results show that the change in soil concentration during the tracer infiltration process can be captured by establishing the fitting relationship between soil resistivity and solute concentration. Then the solute breakthrough curve can be found. Through a time moment analysis, the difference between the breakthrough curve parameters obtained by the traditional method and the resistivity method is slight; the average error is less than 10%. On this basis, the sensitive response of the parameters of the “mobile–immobile” model to concentration was elucidated through different concentration tracer experiments, among which β and D are more sensitive, and w is less sensitive. The suitable tracer concentration range should be 50–120 mg/L. Therefore, the established method could obtain the breakthrough curves and describe the transport of preferential solutes at the field scale.

Historic Underground Silver Mine Workings Detection Using 2D Electrical Resistivity Imaging (Durango, Mexico)

This paper presents an underground silver mining operation outside Gomez Palacio, Durango, Mexico, terminated around the 1930s, of which previous knowledge of its operations was poor. Durango’s current silver exploration campaigns are likely to overlook historic silver mining sites due to interest in specific prospect regions. A two-dimensional (2D) Electrical Resistivity Imaging (ERI) survey coupled with reconnaissance of the area was performed at this historic silver mining site. The exploration campaign aimed to find the abandoned mineshaft, map its subsurface extent, and explore the occurrence of mineralization zones (silver ore). The ERI survey comprised five profiles measured with the extended dipole-dipole array with a consistent electrode spacing of 5 m. The smooth, robust, and damped least-squares inversion methods were used to invert the 2D data. Our field observations and ERI survey results collectively reveal the following findings: (a) reconnaissance reveals mining infrastructure consistent with historical mining activity; the infrastructure includes a complex of habitational rooms, an ore-processing pit near a concrete slab next to a dirt road, and two limestone-wall structures interpreted as the entrance of abandoned backfilled mineshafts named Mesquite and Lechuguilla; (b) high-resistivity anomalies suggest vestiges of shallow, underground mine workings including backfilled mineshafts that connect a mine gallery complex, and (c) various low-resistivity anomalies, juxtaposed against mine galleries, suggestive of unmined shallow vein-type and manto-type mineralization of hydrothermal origin. The imaging depth is estimated at ~65 m. Underground silver mining moved southwards and was limited to ~40 m depth.

Remote Sensing, Geophysics, and Modeling to Support Precision Agriculture—Part 2: Irrigation Management

Food and water security are considered the most critical issues globally due to the projected population growth placing pressure on agricultural systems. Because agricultural activity is known to be the largest consumer of freshwater, the unsustainable irrigation water use required by crops to grow might lead to rapid freshwater depletion. Precision agriculture has emerged as a feasible concept to maintain farm productivity while facing future problems such as climate change, freshwater depletion, and environmental degradation. Agriculture is regarded as a complex system due to the variability of soil, crops, topography, and climate, and its interconnection with water availability and scarcity. Therefore, understanding these variables’ spatial and temporal behavior is essential in order to support precision agriculture by implementing optimum irrigation water use. Nowadays, numerous cost- and time-effective methods have been highlighted and implemented in order to optimize on-farm productivity without threatening the quantity and quality of the environmental resources. Remote sensing can provide lateral distribution information for areas of interest from the regional scale to the farm scale, while geophysics can investigate non-invasively the sub-surface soil (vertically and laterally), mapping large spatial and temporal domains. Likewise, agro-hydrological modelling can overcome the insufficient on-farm physicochemical dataset which is spatially and temporally required for precision agriculture in the context of irrigation water scheduling.

Fingerprinting Organochlorine Groundwater Plumes Based on Non-Invasive ERT Technology at a Chemical Plant

The refined characterization of groundwater pollution is an important prerequisite for efficient and effective remediation. A high-resolution survey of a contaminated site in a chemical pesticide factory was carried out using non-invasive geophysical sensing technology. Modern electrical resistivity tomography (ERT) technology can rapidly identify and characterize the groundwater pollution plumes of organochlorine pesticides, which was demonstrated in this study by the significantly abnormal resistivity sensing in stratums and aquifers under the raw material tanks, production, and loading areas. The results were found to be highly consistent with the ERT sensing results achieved via incorporating borehole sampling and hydrochemical analysis. With high abnormal resistivity, the range of contamination within the profile was characterized on the meter level. We also unexpectedly found new pollution and explained its source. This study confirmed that the modern refined ERT method has a high feasibility and accuracy in characterizing the spatial distribution of organochlorine pesticide plumes in groundwater.

Adsorption of Arsenic on Fe-Modified Biochar and Monitoring Using Spectral Induced Polarization

This work demonstrates the potential of Fe-modified biochar for the treatment of arsenic (As) simulated wastewater and the monitoring of adsorption in real-time. Specifically, we propose the utilization of date-palm leaves for the production of biochar, further modified with Fe in order to improve its adsorption function against inorganic pollutants, such as As. Both the original biochar and the Fe-modified biochar were used for adsorption of As in laboratory batch and column experiments. The monitoring of the biochar(s) performance and As treatment was also enhanced by using the spectral induced polarization (SIP) method, offering real-time monitoring, in addition to standard chemical monitoring. Both the original and the Fe-modified biochar achieved high removal rates with Fe-modified biochar achieving up to 98% removal of As compared to the 17% by sand only (control). In addition, a correlation was found between post-adsorption measurements and SIP measurements.

Geophysical and Geochemical Characterization of Solidwaste Dumpsite: A Case Study of Chowa Gujar, Peshawar (Part of Indus Basin)

Open and non-engineered dumping is a typical method for solid waste disposal in most cities of Pakistan. This practice of waste dumping poses a serious threat to the surrounding ecosystem and human population due to the release and transport of decomposed organic matter, i.e., leachate from dumpsite into the groundwater. The present study was conducted over a non-engineered and open dumpsite (Chowa Gujar), located in the outskirts of the highly populated city of Peshawar by using integrated geophysical techniques such as electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) and geochemical techniques. The main goal was to delineate the characterization and depth of buried waste, to map the subsurface extension of contaminant plumes towards agricultural land and groundwater table and the concentration of heavy metals (HMs) in dump and agricultural soil. Geophysical results showed that the thickness of buried waste (predominantly composed of domestic waste) was around 4 m and the leachate plumes have percolated to the adjacent agricultural land. A range of heavy metals (mg/kg) such as Cr (20.5–26.6), Cd (2.6–5.7), Pb (0.35–21.25), Ni (2.5–53.05), Cu (29–68.3), Zn (45.7–77), and Co (18.9–23.2) have been found in the agricultural land adjacent to the dumpsite. The findings demonstrated that combined use of ERT and GPR successfully characterize the buried waste and spread of pollutant plumes spatially and vertically from Chowa Gujar dumpsite. The anomalous geophysical signatures were confirmed by geochemical characterization. The movement of leachate plumes towards agricultural land and groundwater table and the concentration of HMs in soil show that Chowa Gujar dumpsite is a potential source of contamination not only to the surrounding population but also to the agricultural land, surface (Bara River), and subsurface water bodies. In the study region, there is an urgency to take remediation and mitigation measures to reduce the level of pollution created by the dumpsite.

A multidisciplinary approach for delineating wastewater flow paths in shallow groundwater aquifers: A case study in the southeastern part of the Nile Delta, Egypt

Groundwater pollution is a global issue in highly populated areas, the Eastern Nile Delta region is a typical example; especially around artificial wastewater drains. In the present work, a multidisciplinary approach using hydrogeochemical, geostatistical, microbiological and geophysical data was applied to determine the vulnerability conditions and to identify potential pathways through which contaminants could potentially percolate to shallow aquifers in the southern boundary of the Eastern Nile Delta. An organized groundwater sampling was conducted for hydrogeochemical investigation in rural areas along the Belbies unlined drain. This drain is known of being heavily polluted by agricultural and municipal wastewater. The hydrogeochemical analysis reveals high pollution levels by Pb, Cd, and Cr for most of the collected shallow groundwater samples nearby the drain. Additionally, NO₃^-, fecal and total coliform bacteria were observed in many samples with high concentrations. Six factors were distinguished on the basis of principal component analysis and varimax rotation, with total variance more than 78%. These factors reflected sewage contamination, lithogenic and anthropogenic effects on the shallow groundwater. Hierarchical cluster analysis revealed two main clusters of groundwater groups. Accordingly, Electrical Resistivity Tomography (ERT) was carried out in the areas of the distinguished clusters to locate potential preferential flow paths and horizons of lateral flow around the drain. The obtained resistivity models illustrate breakthrough behavior in parts of the measured profiles due to the presence of permeable paths close to the drain. The applied integrative approach is valuable for understanding the ambiguities during the interpretation process and for characterizing water quality and the aquifer vulnerability conditions. Additionally, it may guide to understand the surface water-groundwater links in order to supply the growing population with safe water.

Investigating the Structure of a Coastal Karstic Aquifer through the Hydrogeological Characterization of Springs Using Geophysical Methods and Field Investigation, Gökova Bay, SW Turkey

The electrical resistivity tomography method has been widely used in geophysics for many purposes such as determining geological structures, water movement, saltwater intrusion, and tectonic regime modeling. Karstic springs are important for water basin management since the karst systems are highly complex and vulnerable to exploitation and contamination. An accurate geophysical model of the subsurface is needed to reveal the spring structure. In this study, several karst springs in the Gökova Bay (SW, Turkey) were investigated to create a 3D subsurface model of the nearby karstic cavities utilizing electrical resistivity measurements. For this approach, 2D resistivity profiles were acquired and interpreted. Stratigraphically, colluvium, conglomerate, and dolomitic-limestone units were located in the field. The resistivity values of these formations were determined considering both the literature and field survey. Then, 2D profiles were interpolated to create a 3D resistivity model of the study area. Medium-large sized cavities were identified as well as their locations relative to the springs. The measured resistivities were also correlated with the corresponding geological units. The results were then used to construct a 3D model that aids to reveal the cavity geometry in the subsurface. Additionally, several faults are detected and their effect on the cavities is interpreted.

Long-term geophysical monitoring of an abandoned dumpsite area in a Guarani Aquifer recharge zone

Even though attenuation processes in the subsurface are known to reduce the impacts of contaminant plumes, their importance is significantly dependent on geological and climatic characteristics, as well as on the leachate quality. The knowledge of attenuation processes linked to different geological formations is therefore fundamental in predicting the impacts of waste disposal areas. Geophysical methods are useful tools for assessing and delineating contaminant plumes, as well as their changes with time, which enables their lower-cost monitoring and association with geological and environmental properties. This paper shows the results of geophysical surveys conducted in the years of 1996, 2005 and 2018 in a waste disposal area located at a Guarani Aquifer recharge zone in Brazil. The objective of this study was to show the evolution of the contamination plume, as well as discuss some possible transport and attenuation processes that the contaminants may undergo in similar areas. Five geophysical sections surveyed within a time span of 20 years were compared, and the information was integrated with physicochemical data from monitoring wells. The results show a horizontal plume spreading, reaching about 200 m from the deposit and about 60 m of depth, 20 years after the ending of disposal activities. The measured resistivities in 2018 are similar to the ones found in 1996 and 2005 in the same surveyed areas, showing that a significant temporal attenuation did not occur. Moreover, samples collected close to anomaly zones and within a distance of 200 m from the deposit presented concentrations of some heavy metals above the screening values according to the Brazilian legislation, showing a metals mobility higher than previously expected, which can be possibly explained by the aquifer's acidic conditions. The estimated plume velocity was about 7 m/yr, a plume deepening was observed until about 50 m and changes in water flow direction and/or diffusion processes made the plume spread to areas previously regarded as upgradient. Therefore, the present paper shows that the rehabilitation of sites neighboring waste disposal sites (less than 200 m from it) did not seem to be feasible through natural attenuation in sandy soils and that the plume spreading is significant in this geological formation. Thus, abandoned disposal areas, constantly considered to be closed after the ending of disposal activities in developing countries, generate plumes which move silently and may reach areas of concern in the future.

Delineation of contaminated aquifers using integrated geophysical methods in Northeast Punjab, Pakistan

A decline in surface water sources in Pakistan is continuously causing the over-extraction of groundwater resources which is in turn costing the saltwater intrusion in many areas of the country. The saltwater intrusion is a major problem in sustainable groundwater development. The application of electrical resistivity methods is one of the best known geophysical approaches in groundwater study. Considering the accuracy in extraction of freshwater resources, the use of resistivity methods is highly successful to delineate the fresh-saline aquifer boundary. An integrated geophysical study of VES and ERI methods was carried out through the analysis and interpretation of resistivity data using Schlumberger array. The main purpose of this investigation was to delineate the fresh/saline aquifer zones for exploitation and management of fresh water resources in the Upper Bari Doab, northeast Punjab, Pakistan. The results suggest that sudden drop in resistivity values caused by the solute salts indicates the saline aquifer, whereas high resistivity values above a specific range reveal the fresh water. However, the overlapping of fresh/saline aquifers caused by the formation resistivity was delineated through confident solutions of the D-Z parameters computed from the VES data. A four-layered unified model of the subsurface geologic formation was constrained by the calibration between formation resistivity and borehole lithologs. i.e., sand and gravel-sand containing fresh water, clay-sand with brackish water, and clay having saline water. The aquifer yield contained within the fresh/saline aquifers was measured by the hydraulic parameters. The fresh-saline interface demarcated by the resistivity methods was confirmed by the geochemical method and the local hydrogeological data. The proposed geophysical approach can delineate the fresh-saline boundary with 90% confidence in any homogeneous or heterogeneous aquifer system.

Multidisciplinary Characterization of Chlorinated Solvents Contamination and In-Situ Remediation with the Use of the Direct Current Resistivity and Time-Domain Induced Polarization Tomography

Soil contamination is a widespread problem and action needs to be taken in order to prevent damage to the groundwater and the life around the contaminated sites. In Sweden, it is estimated that more than 80,000 sites are potentially contaminated, and therefore, there is a demand for investigations and further treatment of the soil. In this paper, we present the results from a methodology applied in a site contaminated with chlorinated solvents, for characterization of the contamination in order to plan the remediation and to follow-up the initial step of in-situ remediation in an efficient way. We utilized the results from three different methods; membrane interface probe for direct measurement of the contaminant concentrations; seismic refraction tomography for investigating the depth to the bedrock interface; and direct current resistivity and time-domain induced polarization tomography to acquire a high-resolution imaging of the electrical properties of the subsurface. The results indicate that our methodology is very promising in terms of site characterization, and furthermore, has great potential for real-time geophysical monitoring of contaminated sites in the future.

Mapping the contaminant plume of an abandoned hydrocarbon disposal site with geophysical and geochemical methods, Jiangsu, China

The management and remediation of abandoned hydrocarbon-contaminated sites require detailed information on the distribution of contaminant plumes. In areas where groundwater is active, the formation of contaminant plumes is associated with hydrodynamics, the nature of the sedimentary layers, and the nature of the pollutants and the degradation process. A comprehensive survey is needed to determine this information. An abandoned hydrocarbon disposal site is located in an area where groundwater is very active. In the investigation of contaminant plumes, we combined the geophysical method with accurate geochemical analysis of subsoil and groundwater samples. Ground-penetrating radar and electrical resistivity tomography images of the electrical anomalies potentially originating from hydrocarbon pollution were used to select sites for subsurface sampling. Total petroleum hydrocarbons, total dissolved solids, and groundwater pH were measured. The results showed that the source zone had undergone long-term natural attenuation, and it was unable to continuously output organic matter to support the expansion of contaminant plumes. Low-resistivity anomalies and enhanced attenuation in the study area were caused by hydrocarbon degradation products and enhanced mineral weathering. Delineating the distribution of contaminant plumes in areas where the resistivity was below 15 Ω m. The distribution of the plume in the vertical direction was related to the hydrocarbon release history (release rate and volume) and was affected by fluctuations in the groundwater level. The contaminant plume moved very slowly along the direction of the hydraulic gradient and was in a basically stable state. The results showed that the combined application of the geoelectrical method and the geochemical method can effectively describe the distribution of underground contaminant plumes in an aged pollution site.

Predicting spatial distribution of heavy metals in an abandoned phosphogypsum pond combining geochemistry, electrical resistivity tomography and statistical methods

One of the wastes generated in fertiliser production from phosphoric rock is phosphogypsum, whose mismanagement lead to environmental and health risks. Therefore, a detailed evaluation of the chemical composition of phosphogypsum is necessary to determine effective means of its management. Due to the high amount of generated waste, the cost and time consumed for this characterisation by chemical analysis is limiting. Hence, efficient tools should be developed to predict the chemical composition of this waste. Thus, this study aims to: 1) determine the physic-chemical characterisation of phosphogypsum pond using geochemical and geophysical techniques and 2) predict the heavy metals spatial distribution through statistical models. Results show that the most concentrate metal is chromium with a maximum of ≈900 mg.kg^-1 and cadmium is the least concentrated (maximum ≈23 mg.kg^-1). The Electrical Resistivity Tomography revealed the superposition of two layers. The top one (waste) presents low resistivity (≈17Ω.m) while the bottom layer shows higher resistivity (>124Ω.m). Metal concentrations and resistivities were combined by applying non-linear regression models. Cr showed the strongest correlation (R² = 0.68), yielding an accurate model that was used for revealing the spatial distribution of the highest Cr concentrations in the pond, with the consequent reduction of expensive traditional methods.