Contaminant Plume Research Articles

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

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.

Monitoring time evolution of self-potential anomaly sources by a new global optimization approach. Application to organic contaminant transport

Complex interactions among organic contaminant, soil and water change the electrical properties of the subsurface often causing strong self-potential (SP) anomalies, whose monitoring is proposed as a useful tool to determine the temporal evolution of the contaminant plumes. In the present study, we focus on the problem of organic contaminant transport related to olive oil mill wastes (OOMWs), which represent an important environmental problem in Mediterranean countries. The diffusion of the contaminants into the subsurface is studied by using a global optimization procedure on SP data measured, at different times, in a well-studied contaminated pilot area located next to the Keritis river in western Crete island (Greece). Despite the complex hydrogeological conditions related to the proximity to both the Keritis river and a small seasonal stream, the analysis of five SP datasets acquired along the same profile shows that the proposed hybrid Genetic-Price algorithm is able to reproduce the main features of the SP signals, thus identifying probable multiple SP anomaly sources and their changes over time. In particular, preferential horizontal pathways of OOMW and their migration in the vadose zone during the summer season were identified, providing some useful insights for future planning of remediation actions.

Analysis of radially convergent tracer test in a two-zone confined aquifer with vertical dispersion effect: Asymmetrical and symmetrical transports.

Radially convergent tracer test (RCT) with an extraction well and a tracer injection well is commonly conducted for determining aquifer dispersivity associated with the spreading of contamination plume. A variety of analytical models for RCT have been proposed, but the effects of skin zone and vertical dispersion are rarely explored. In addition, little attention is paid to the validity of those analytical models assuming asymmetrical tracer transport (ATT) as radially symmetrical transport (RST) toward the pumping well. This study develops a new analytical model for RCT subject to the above-mentioned effects in a confined aquifer with a skin zone around the wellbore. The Laplace-domain solution of the model for a continuous or instantaneous input is developed. A finite element solution (FES) for ATT is also developed to verify the Laplace-domain solution based on RST. Results suggest ATT can be regarded as RST in predicting the breakthrough curve (BTC) at the pumping well when four quantitative conditions are met. A lumped dimensionless parameter dominates those two effects on the BTC. Both the FES and Laplace-domain solution agree with monitored concentration data from a field RCT.

Express yourself: Individuals with bold personalities exhibit increased behavioral sensitivity to dynamic herbicide exposure

The majority of ecotoxicological studies performed measure average responses from individuals which do not account for the inter-individual variation in the responses of animals to environmental stimuli (i.e. the personality of individuals). Thus, these designs assume that all individuals will respond to contaminant exposure in a similar manner. Additionally, commonly used constant, static exposure regime designs neglect to recognize the spatial and temporal variation in contaminant plume structures as they move throughout fluid environments. The purpose of this study was to understand the effects of the structural characteristics (concentration, duration, and frequency) of temporally and spatially variant contaminant plumes on the personality of individuals. This experimental design aimed to construct a sensitive definition of exposure by connecting sublethal effects of toxicants and realistic exposure regimes. This study used escape response of Faxonius virilis crayfish from the predatory odor of Micropterus salmoides prior to and following exposure to the herbicide, atrazine. Atrazine was delivered in pulses to flow through exposure arenas for a total of 47 h while manipulating the concentration, frequency, and duration of the herbicide pulses. Escape response of crayfish prior to exposure was used to categorize animals into bold and shy personalities. The change in escape response was analyzed and resulted in a personality-dependent behavioral sensitivity to the polluted environment. Individuals classified as bold showed increased change in response to predatory odor relative to shy animals. Bold animals exhibited decreased activity after exposure where no change was presented in shy individuals. Shifts in individual behavior have impacts on the population level (e.g. resource acquisition/value; interspecies competition) and the ecosystem level (e.g. food web dynamics; trophic cascades). This study demonstrates the importance of sensitive measures in ecological risk assessment methods.

The fate of DNAPL contaminants in non-consolidated subsurface systems – Discussion on the relevance of effective source zone geometries for plume propagation

Dense non-aqueous phase liquids, i.e., DNAPLs and the evolving contaminant plumes in aquifers provide significant potential to pose hazards affecting both environment and human health. Therefore, a proper assessment of contaminant spreading within the subsurface is critical. This includes a sufficient characterization of governing parameters describing both the subsurface and the contaminant itself. Thereby, knowledge on the contaminant source zone and especially the source zone geometry, i.e., SZG is critically required, yet very uncertain. This study identifies current limitations and open research questions in the formation and shape determination of source zone geometry, as well as its relevance for contaminant plumes. Our literature review reveals that existing characterization methods are subject to data interpretation uncertainties, while the application of these methods on field scale is limited by technical demands and accompanied efforts. In a next step, methods to implement increased source zone information into calculation methods are discussed. By means of an exemplary application of selected assessment tools, i.e., plume response models, results clearly proof the relevance of SZGs for site assessment. However, existing plume response models consider over-simplified geometries that may compromise their suitability. Our findings identify the demand for improved characterization of complex SZGs and the need to better evaluate the dependency of DNAPL migration on system properties and external influences. With emphasized knowledge on the most relevant SZG features, the delineation of "effective" SZGs allowing for straightforward implementation into plume response models and an adaption of the latter to incorporate more information on SZGs should be possible.

A framework for conceptualizing groundwater-surface water interactions and identifying potential impacts on water quality, water quantity, and ecosystems

Developing an understanding of how groundwater (GW) and surface water (SW) systems function and interact to impact water quantity, water quality, and ecosystem health provides a basis for management of water resources, environmental protection, and land management. Although knowledge of these complex and dynamic systems has improved in recent decades, there is currently no systematic guidance for conceptualizing and evaluating GW-SW interactions and identifying their potential impact on management issues. For this reason, a holistic framework was created to provide a comprehensive and logical approach for identifying, understanding, and evaluating the key factors and processes controlling GW-SW interactions and understanding their relationship to environmental problems. The framework identifies fundamental hydrological, biogeochemical, and biological processes and critical factors to consider when developing robust conceptual models of GW-SW systems. The framework is comprehensive and can be adapted to different problems using only the aspects necessary to address a specific issue. The framework focuses on streams, rivers, and lakes but can be adapted for use in other GW-SW settings such as ponds, wetlands, and coastal marine environments. Applicability of the framework is illustrated through evaluation of three GW-SW interaction settings in southern Ontario, Canada: a groundwater contaminant plume discharging to the Pine River, discharge of groundwater nutrients to Lake Huron, and a regional-scale conceptualization of GW-SW flow interactions in the Duffins Creek watershed. The case studies highlight flexibility of the framework to develop conceptual models, assess environmental issues, identify knowledge gaps, and provide a basis for designing site investigations.

Plume of oil metabolites in groundwater: formation, evolution, and toxicity

The transformation of oil hydrocarbons in groundwater is mainly related to the processes of biodegradation. At sites where residual crude oil or petroleum hydrocarbon fuel contaminants are present in the environment, biodegradation reactions result in the formation of partial oxidation products, i.e., metabolites. These transformation products are more soluble than the parent petroleum hydrocarbons, due to their greater polarity and corresponding low volatility. Transformation products from residual source zones are distributed in aqueous phase to form a plume of contamination in groundwater. The content of metabolites depends on the redox conditions and the presence of the terminal electron acceptors, as well as on the structure of the original hydrocarbon compounds. The article considers the conditions for formation of metabolites, their degradation, migration to groundwater and plume formation, toxicity of metabolites. Examples of modeling the migration of metabolites in the saturated zone are given.

Forty-year evolution of radioactive groundwater contamination at the site of radioactive waste storage (St. Petersburg region, Russian Federation)

Evolution of tritium and beta contamination plumes resulted from radioactive waste leakage in the 1990s has been studied based on 40-year-long monitoring data at the site of radioactive waste (RW) storage. Localand regional-scale hydrodynamics are found to be the main features controlling the spreading of tritium contamination in the aquifer system, while spatial distribution of beta-activity plume is strongly restricted by sorption of 90Sr и 137Cs isotopes onto rock matrix. The study performed proves that groundwater system at the site is actually in the stage of rehabilitation from the «historical» contamination. Special complex investigation program aimed on examination of water accumulated in repository buildings and its interconnection with groundwater, demonstrated good isolation of the buildings from the surrounding aquifers and no evidence of RW release to the subsurface environment nowadays.

Effects of 90Sr on Tree Swallow Nestlings Near Groundwater Contaminant Plumes.

Discharge of groundwater contaminant plumes has created elevated concentrations of Sr in some aquatic sediments at Chalk River Laboratories. Tree swallows (Tachycenita bicolor) feed and supply their nestlings almost exclusively with airborne insects that developed as larvae in aquatic sediments. To monitor the uptake and test for potential detriment due to Sr in a terrestrial animal, we measured the gross beta concentrations in the bone of 12-d-old tree swallow nestlings in areas having sediments with elevated levels of gross beta (Sr and Y) and in several control areas where sediment gross beta was primarily due to naturally occurring K. Nesting behavior and reproductive success of the tree swallows were similar regardless of the gross beta concentrations in sediments near their nest boxes. Radiation can damage DNA and cause micronuclei to form in cells, so we examined the frequency of micronuclei in erythrocytes of nestlings. The formation of micronuclei in the erythrocytes of the nestlings was also similar wherever nestlings were analyzed. The results revealed no significant increases even near sediments with the highest gross beta levels. At Perch Lake, where Chalk River Laboratories has a large area of Sr-contaminated sediments, the bones of 12-d-old nestlings contained gross beta concentrations as high as 29 Bq g. This would produce a skeletal dose rate of 9 μGy h, which is one-fourth of the threshold dose rate of 40 μGy h, above which detriment could occur. Failing to find any indication of detriment in the field study, we irradiated wild eggs in the lab and returned them to their nest for natural incubation, hatching, and feeding by the parents. There was an increase in formation of micronuclei following a dose of 3.2 Gy, and the other results were consistent with existing literature.

Artificial neural network prediction models of heavy metal polluted soil resistivity

Heavy metal contaminated soil is on the rise in the whole world with the boost of industrialisation and urbanisation. As such, the heavy metal pollution in lands is of attracted considerable concern to professionals and planners. The detection of contaminant plumes in the subsurface is an important aspect of geotechnical and geo-environmental engineering practice. In this regard, a commonly used method involves conducting electrical resistivity measurements is employed to qualitatively delineate suspected contaminated sites subsurface contamination. However, resistivity measurements alone will lead to some degree of ambiguity in the results, and give only qualitative information about the changes in the chemical composition of the soil-pore fluid. In order to generate much confidence in using the resistivity, the better computational algorithms (viz. artificial neural networks) that should be capable of incorporating the interdependence of several parameters must be employed. Artificial neural network (ANN) presents an oversimplified simulation of the human brain and is accepted as a reliable data modelling tool to capture and represent complex relationships between inputs and outputs. With this in view, efforts were made to develop ANN models that can be employed for predicting electrical resistivity by employing different soil properties such as contaminants, ionic concentrations (n), moisture content (w), porosity (φ) and saturation (S r). To demonstrate the efficiency of the ANN models, the results obtained were compared with those obtained from experimental investigations and empirical relationships, which are reported in the literature. In addition, the performance indices such as coefficient of determination, root mean square error, mean absolute error and variance were used to assess the performance of the ANN models.

Dam Operations and Subsurface Hydrogeology Control Dynamics of Hydrologic Exchange Flows in a Regulated River Reach

AbstractHydrologic exchange flows (HEFs) across the river‐aquifer interface have important implications for biogeochemical processes and contaminant plume migration in the river corridor, yet little is known about the hydrogeomorphic factors that control HEFs dynamics under dynamic flow conditions. Here, we developed a 3‐D numerical model for a large regulated river corridor along the Columbia River to study how HEFs are controlled by the interplays between dam‐regulated flow conditions and hydrogeomorphic features of such river corridor system. Our results revealed highly variable intra‐annual spatiotemporal patterns in HEFs along the 75‐km river reach, as well as strong interannual variability with larger exchange volumes in wet years than dry years. In general, the river was losing during late spring to early summer when the river stage was high, and river was gaining in fall and winter when river stage was low. The magnitude and timing of river stage fluctuations controlled the timing of high exchange rates. Both river channel geomorphology and the thickness of a highly permeable river bank geologic layer controlled the locations of exchange hot spots, while the latter played a dominant role. Dam‐induced, subdaily to daily river stage fluctuations drove high‐frequency variations in HEFs across the river‐aquifer interfaces, resulting in greater overall exchange volumes as compared to the case without high‐frequency flows. Our results demonstrated that upstream dam operations enhanced the exchange between river water and groundwater with strong potential influence on the associated biogeochemical processes and on the fate and transport of groundwater contaminant plumes in such river corridors.

Spatial properties of soil analyses and airborne measurements for reconnaissance of soil contamination by 137Cs after Fukushima nuclear accident in 2011

Following Fukushima nuclear disaster, several data gathering campaigns surveyed the radionuclide propagation in the environment. However, the acquired datasets do not have the same sampling dimension. For example, the airborne measurements are some sort of averaging over a circular field of view, beneath the sensor; while the soil analyses are much more punctual. The objective of this work is to compare the soil samples and an airborne survey to investigate whether these two datasets reflect the same spatial patterns or not. This is prerequisite for combining the multiresolution data to create and update the contamination map in a post-accidental situation.The analyses were performed on square tiles of 20 km side to study large- and small-dimension variations in 137Cs deposition. The former was modelled by fitting a plane (called trend) to the georeferenced data points; and the latter was modelled by computing the difference (called residual) between the trend and the initial data. Dip direction and dip angle of trends as well as minimum spatial correlation distance and anisotropy of residuals were computed for both the soil and airborne datasets and compared. Dip directions are compatible in 73% of the tiles and dip angles are generally close. Anisotropy directions are compatible in 49% of the tiles and minimum spatial correlation distances are significantly more marked for the airborne dataset.The soil samples and airborne measurements are therefore more in agreement in large-dimension (trend) rather than in small-dimension (residual) variations. More generally, both the datasets allow highlighting the main contamination plumes distinguishable because of high concentration values. The airborne dataset yet appears to be more powerful to quantify spatial correlations, which could be linked to the contamination mechanisms.

Influence of buoyancy forces on movement of liquid radioactive waste from deep injection disposal site in the Tomsk region, Russian Federation: analytical estimate and numerical modeling

Deep injection disposal of liquid hazardous waste into aquifers confined from top and bottom by low permeable rock layers is examined. The injected waste represents aqueous solutions which are more dense than the reservoir water. Since the aquifer is not strictly horizontal, heterogeneity of the groundwater density causes a resultant buoyancy force which is directed down the dip of the aquifer. We considered a mathematical model of the contaminant plume movement taking into account both topography-driven (regional) and buoyancy induced components of the groundwater flow. Boussinesq’s approximation is used. A simple analytical solution, which is obtained by general functions theory, permits to determine conditions when the buoyancy forces suppress the regional flow what can substantially increase safety of the injection disposal. The obtained result is applied to analysis of contaminant plume movement at injection disposal site of liquid radioactive waste from Siberian Chemical Plant in Tomsk region. A numerical modeling of plume movement at the injection site is carried out. Heterogeneity of water transmissivity of the reservoir bed is taken into account as well as heterogeneous relief of its upper and lower boundaries. We showed on the basis of the analytical solution that buoyancy forces caused by elevated salinity of the injected waste and slope of the reservoir bed at the injection site exert a substantial influence on direction of the contaminant plume movement. Numerical modeling of contaminant plume movement is in good agreement with the analytical estimation of the buoyancy forces influence. Velocity of the regional groundwater flow is directed to the southwest of the injection site. However only dilute solutions are carried southwest by the regional flow. Dense solutions move westward because the buoyancy forces hamper southern component of the regional flow. This leads to an increase in travel time of a substantial part of the radionuclides to the river what increases safety of the injection site.

Modeling groundwater contaminant transport in the presence of large heterogeneity: A case study comparing MT3D and RWhet.

A case study is presented that implements two numerical models for simulating a 30-year PAT operation conducted at a large contaminated site for which high-resolution data sets are available. A Markov chain based stochastic method is used to conditionally generate the realizations with random distribution of heterogeneity for the Tucson International Airport Area (TIAA) federal Superfund site. The fields were conditioned to data collected for 245 boreholes drilled at the site. Both MT3DMS and the advanced random walk particle method (RWhet) were used to simulate the PAT-based mass removal process. The results show that both MT3DMS and RWhet represent the measured data reasonably, with Root Mean Square Error (RMSE) less than 0.03. The use of fine grids and the total-variation-diminishing method (TVD) limited the effects of numerical dispersion for MT3DMS. However, the effects of numerical dispersion were observed when compared to the simulations produced with RWhet using a larger number of particles, which provided more accurate results with RMSE diminishing from 0.027 to 0.024 to 0.020 for simulations with 1, 20, and 50 particles. The computational time increased with more particles used in the model, but was still much less than the time required for MT3DMS, which is an advantage of RWhet. By showing the results using both methods, this study provides guidance for simulating long-term PAT systems. This work will lead to improve understanding of contaminant transport and plume persistence, and in turn will enhance site characterization and site management for contaminated sites with large plumes.

Influência do lençol freático na condutividade elétrica e PH em cemitério

O sepultamento de corpos humanos em locais sem tratamento e infraestrutura adequada pode impactar o solo e o lençol freático através da infiltração e percolação do necrochorume, visto que estando o lençol freático em contato com a pluma de contaminação ocorre a solubilização dos íons presentes no necrochorume o que favorece o enriquecimento de sais, alterando assim a qualidade da água subterrânea. Por este motivo, o objetivo deste estudo foi avaliar o nível do lençol freático na condutividade elétrica e no pH sob influência de um cemitério na região metropolitana de Goiânia (GO). Portanto, foram construídos cinco poços de monitoramento, dos quais levou-se em consideração a declividade do terreno. Após isto realizou-se a coleta da água subterrânea com tubos bailers, bem como o monitoramento do lençol freático entre os meses de março a agosto de 2018, realizou-se em laboratório a análise dos parâmetros de condutividade elétrica e pH das amostras de água dos poços de monitoramento, conseguinte os dados foram inseridos no programa Excel (2013) para confecção dos gráficos. Os resultados obtidos demonstraram que o nível do lençol freático influencia na condutividade elétrica e pH devido as variações da condutividade elétrica e acidificação do pH, sendo assim um indicativo da contaminação da água subterrânea por necrochorume.

Dynamics of Hydrology and Anaerobic Hydrocarbon Degrader Communities in A Tar-Oil Contaminated Aquifer.

Aquifers are typically perceived as rather stable habitats, characterized by low biogeochemical and microbial community dynamics. Upon contamination, aquifers shift to a perturbed ecological status, in which specialized populations of contaminant degraders establish and mediate aquifer restoration. However, the ecological controls of such degrader populations, and possible feedbacks between hydraulic and microbial habitat components, remain poorly understood. Here, we provide evidence of such couplings, via 4 years of annual sampling of groundwater and sediments across a high-resolution depth-transect of a hydrocarbon plume. Specialized anaerobic degrader populations are known to be established at the reactive fringes of the plume. Here, we show that fluctuations of the groundwater table were paralleled by pronounced dynamics of biogeochemical processes, pollutant degradation, and plume microbiota. Importantly, a switching in maximal relative abundance between dominant degrader populations within the Desulfobulbaceae and Desulfosporosinus spp. was observed after hydraulic dynamics. Thus, functional redundancy amongst anaerobic hydrocarbon degraders could have been relevant in sustaining biodegradation processes after hydraulic fluctuations. These findings contribute to an improved ecological perspective of contaminant plumes as a dynamic microbial habitat, with implications for both monitoring and remediation strategies in situ.

Fuzzy-based conflict resolution management of groundwater in-situ bioremediation under hydrogeological uncertainty

In this research study, a fuzzy multi-objective optimization methodology is proposed for in-situ groundwater bioremediation utilizing the Graph Model for Conflict Resolution. In the current model, uncertainties in hydraulic conductivity and the ratio of transverse to longitudinal dispersivity of contaminants are considered using the Fuzzy Transformation Method (FTM). First, the BIOPLUME III simulation model is linked with a Non-dominated Sorting Genetic Algorithm II (NSGA-II) multi-objective optimization model to optimize a groundwater bioremediation system regarding conflicting viewpoints of decision makers. Then, the hydrogeological uncertainties of the groundwater bioremediation system are included in the proposed methodology using FTM. The three main objectives of the in-situ bioremediation optimization model are overall cost (well installation, treatment or pumping, and facility capital), the sum of contaminant concentration violating any standards, and contaminant plume fragmentation, which need to be minimized based on stakeholders’ preferences. Subsequently, GMCR II is utilized to resolve any conflicts between the perspectives of the stakeholders to achieve a compromise solution. The performance assessment results represent the ability of the proposed methodology for optimal in-situ groundwater bioremediation. Results show that the minimum fuzzy interval is 32.5%, and pertains to the overall cost of the bioremediation system in fuzzy α-cut levels of 0 and 0.5. Conversely, the maximum fuzzy interval is related to contaminant plume fragmentation in fuzzy α-cut levels of 0 and 0.5, and was found to be 95.1%.

Slow-release permanganate versus unactivated persulfate for long-term in situ chemical oxidation of 1,4-dioxane and chlorinated solvents

The objective of this research was to evaluate slow-release permanganate and unactivated persulfate for in situ treatment of dioxane and associated chlorinated solvents. Laboratory batch studies with unactivated persulfate in deionized water or in soil and groundwater demonstrated dioxane removal with pseudo second-order rate constants ranging from 10−5 to 10−3 M−1 s−1. Flow-through column studies demonstrated over 99% dioxane removal with slow-release unactivated persulfate but not with slow-release permanganate. The slow-release permanganate cylinders became coated with a rind that limited oxidant mass transfer and dioxane oxidation. A field study was conducted with slow-release persulfate cylinders transverse to groundwater flow. Over 99% removal of dioxane and chlorinated solvents was observed 2.5 m downgradient of the cylinders. Density-driven flow associated with the released persulfate was observed and was attributed to a low horizontal hydraulic gradient. Thus, most of the contaminant and persulfate flux was thought to be isolated to a deep aquifer zone that was bound by an underlying silt aquitard. Contaminant reductions were also observed in shallow groundwater samples, albeit at a lesser extent. The longevity of the persulfate oxidant cylinders was estimated to be 6–12 months. Results of this study demonstrate that dioxane and co-mingled chlorinated solvents can be effectively treated using slow-release persulfate cylinders. Careful consideration to cylinder placement during the design phase is essential to prevent the contaminant plume from bypassing and not coming into contact with the released oxidant.

Environmental study of the dump of the tracuateua city (Pará, Brazil) using ground penetrating radar

The excessive growth of human populations in recent years, associated with the unbridled expansion of consumerism, has led to an ongoing increase in the disposal of solid waste, raising concerns in the scientific community, and highlighting the need for research on the environmental impacts caused by this process. Human populations exploit natural resources across wide areas for agriculture and urban and industrial development. The present, preliminary study in the municipality of Tracuatuea in Para, northern Brazil, focuses on an unregulated open dump located within a large tract of natural vegetation, and in the proximity of water resources (i.e. streams, rivers). Ground Penetrating Radar (GPR) was used to investigate the subsurface, and detected the presence of a plume of contamination that reaches a possible water table. The results of this study provided important insights into potential contamination of the subsurface of the study area, which should serve as an alert for the local population and municipal authorities.

Numerical methods and analysis for a multi-term time–space variable-order fractional advection–diffusion equations and applications

Field experiments of solute transport through heterogeneous porous and fractured media show that the growth of contaminant plumes may convert between diffusive states. In this paper, we propose a multi-term time–space variable-order fractional advection–diffusion model (MTT-SVO-FADM) to describe the underlying transport dynamics. We consider a numerical approach based on the implicit numerical method for numerical solution of this model. A fully-discrete numerical scheme is developed by using the classical finite difference method. The unconditional stability and convergence of the scheme are discussed and theoretically proved. We use a modified grid approximation method (MGAM) to estimate the model’s parameters. The MTT-SVO-FADM is then applied to describe transient dispersion observed at a field tracer test and four numerical experiments. The results show that this model can simulate the experimental data more accurately and can efficiently quantify these transitions. • A multi-term time–space variable-order fractional advection–diffusion model is proposed. • A fully-discrete numerical scheme is developed. • The unconditional stability and convergence of the scheme are discussed and proved. • A modified grid approximation method is used to estimate the model’s parameters. • This model is applied to describe transient dispersion observed at a field tracer test and four numerical experiments.