Pollution Plume Research Articles

Monitoring Stresses Caused by Gaseous Pollutants: How Can They Affect a Fruit-Feeding Butterfly Community (Lepidoptera: Nymphalidae) in the Caatinga?

This study evaluated the effects of gaseous pollutants and vegetation on the structure of fruit-feeding butterfly communities (some subfamilies of Nymphalidae) in a Caatinga area in Brumado, BA, between 2016 and 2018. Two transects were established: Transect “I” (presence of pollutant plumes) and Transect “II” (absence), encompassing a forest fragment and pasture. Bait traps were installed in each transect, and the butterfly communities were analyzed using faunistic indices, including species richness, Shannon diversity index, abundance, and dominance. The canopy opening was also assessed. The composition of fruit-feeding butterfly communities was influenced by both pollutants and vegetation. Gaseous pollutants increased butterfly abundance, diversity, and species richness, though species dominance remained unaffected. Notably, the abundance of Hamadryas februa was particularly sensitive to pollutant exposure. Conversely, increased canopy opening was negatively associated with butterfly abundance and diversity. A relationship between canopy opening and the presence of gaseous pollutants may reflect changes in the abundance and diversity of fruit-feeding butterfly species in the study region. Long-term community monitoring is important, as interannual differences in population fluctuations are common. A better understanding of the patterns found is essential to for devise devising conservation strategies for frugivorous butterfly communities in mining ventures.

A Numerical Study on Impact of Coal Mining Activity and Mine Water Drainage on Flow and Transport Behavior in Groundwater

Under the dual carbon mission, more and more coal mines will face shutting down in the future and stop treating mine water drainage, which, if it escapes, may cause severe secondary damage to the local groundwater quality. Wudong Coal Mine is a currently active subsurface coal mine in Xinjiang, China, that shows high-salinity characteristics. To forecast and discuss future possible groundwater quality damages and potential solutions, we here introduce a model prediction study on the effects of water pollution by coal mine drainage. The study protocol first involves creating a calibrated 2D groundwater flow model by use of FEFLOW software, then designing several flow and solute transport prediction analyses under changing mine water drainage conditions, different pollution source areas and water treatment pumping wells to discuss future prominent flow and transport behavior, as well as water treatment-affecting factors. It has been shown that mine water drainage plays a critical role in maintaining the mine water solute distribution, as without mine draining, local flow and solute distribution change dramatically, altering the groundwater capture zone, and may change the plume-migrating direction from upstream to downstream. A larger pollution source could produce a higher concentration of pollutants and a larger pollution-coverage area. To reduce pollutant concentrations, mine water treatment pumping wells with higher pumping rates can be applied as a useful remedial measure to effectively prevent the pollutant plume front from reaching the important drinking and irrigation water source of the region, Urumqi River. The results of this study can give important suggestions and decision-making support for authorities focused on water treatment and environmental protection decision-making in the region.

Numerical Simulation of Airflow and Pollutant Dispersion Around High-Rise Buildings with Different Rotation Angles

The increase in urban building density will have a significant impact on pedestrian wind environments, especially in high-density urban building environments. Architectural designers should consider the impact of the urban microclimate through reasonable architectural designs and layouts, effectively improve the pedestrian wind environment, and enhance the comfort of urban dwellers and the sustainable development of cities. Therefore, on the basis of the Reynolds number average Navier–Stokes (RANS) method, a standard k-ε turbulence model was adopted to simulate the effects of high-rise buildings with different rotation angles on the flow and dispersion of pollutants. The results showed that the rotation angle has an obvious influence on the flow structure, turbulent kinetic energy, and near-ground concentration, and the effect is more significant with the increase in building height. When the building is rotated by a certain angle (10°, 20°, and 30°), the whole flow is deflected and no longer symmetrical. When the rotation angles are 20° and 30°, it is found that two large vortices are formed in the wake region of the entire building array, as if the building array can be regarded as a whole. Because the pollution source is located in the recirculation zone or the reverse-flow zone, the high-concentration area is mainly concentrated upwind of the source. As the building is rotated counterclockwise (10°, 20°, and 30°), the pollutant plume is also deflected counterclockwise, presenting an asymmetry.

The differences between remote sensing and in situ air pollutant measurements over the Canadian oil sands

Abstract. Ground-based remote sensing instruments have been widely used for atmospheric research, but applications for air quality monitoring remain limited. Compared to an in situ instrument that provides air quality conditions at the ground level, most remote sensing instruments (nadir viewing) are sensitive to a broad range of altitudes, often providing only integrated column observations. These column data can be more difficult to interpret and to relate to surface values and hence to “nose-height-level” health factors. This research utilized ground-based remote sensing and in situ air quality observations in Canada's Athabasca oil sands region to investigate some of their differences. Vertical column densities (VCDs) of SO2 and NO2 retrieved by Pandora spectrometers located at the Oski-Otin site at Fort McKay (Alberta, Canada) from 2013–2019 were analyzed along with measurements of SO2 and NO2 surface concentrations and meteorological data. Aerosol optical depth (AOD) observations by a CIMEL sunphotometer were compared with surface PM2.5 data. The Oski-Otin site is surrounded by several large bitumen mining operations within the Athabasca oil sands region with significant NO2 emissions from the mining fleet. Two major bitumen upgraders that are 20 km south-east of the site have total SO2 and NO2 emissions of about 40 and 20 kt yr−1, respectively. It was demonstrated that remote sensing data from Pandora and CIMEL combined with high-vertical-resolution wind profiles can provide information about pollution sources and plume characteristics. Elevated SO2 VCDs were clearly observed for times with south and south-eastern winds, particularly at 200–300 m altitude (above ground level). High NO2 VCD values were observed from other directions (e.g., north-west) with less prominent impacts from 200–300 m winds. In situ ground observations of SO2 and NO2 show a different sensitivity to wind profiles, indicating they are less sensitive to elevated plumes than remote sensing instruments. In addition to measured wind data and lidar-observed boundary layer height (BLH), modelled wind profiles and BLH from ECMWF Reanalysis v5 (ERA5) have been used to further examine the correlation between column and surface observations. The results show that the height of emission sources (e.g., emissions from high stacks or near the surface) will determine the ratio of measured column and surface concentration values (i.e., could show positive or negative correlation with BLH). This effect will have an impact on the comparison between column observations (e.g., from the satellite or ground-based remote sensing instruments) with surface in situ measurements. This study explores differences between remote sensing and in situ instruments in terms of their vertical, horizontal, and temporal sampling differences. Understanding and resolving these differences are critical for future analyses linking satellite, ground-based remote sensing and in situ observations in air quality monitoring and research.

Analysis of the day-to-day variability of ozone vertical profiles in the lower troposphere during the 2022 Paris ACROSS campaign

Abstract. The variability of ozone vertical profiles in the Paris area is analyzed using 21 d of lidar monitoring of the lower-troposphere ozone vertical profiles and planetary boundary layer (PBL) vertical structure evolution in summer 2022. Characterization of the pollution regional transport is based on daily ozone analysis of the Copernicus Atmospheric Service (CAMS) ensemble model and on backward trajectories. The CAMS simulations of the ozone plume between the surface and 3 km are consistent with the ozone measurements. Comparisons with the tropospheric ozone column retrieved by satellite observations of the Infrared Atmospheric Sounding Interferometer (IASI) show that IASI observations can capture the day-to-day variability of the 0–3 km ozone column only when the maximum altitude of the ozone plume is higher than 2 km. The lidar ozone vertical structure above the city center is also in good agreement with the PBL growth during the day and with the formation of the residual layer during the night. The analysis of four ozone pollution events shows that the thickness of the PBL during the day and the advection of regional-scale plumes above the PBL can significantly change the ozone concentrations above Paris. Advection of ozone-poor concentrations in the free troposphere during a Saharan dust event is able to mitigate ozone photochemical production. On the other hand, the advection of a pollution plume from continental Europe with high ozone concentrations > 140 µg m−3 maintained high concentrations in the surface layer despite a temperature decrease and cloud cover development.

Occurance and pollution risk assessment of emerging contaminants in groundwater in the vicinity of a typical municipal landfill in northeastern China

Emerging contaminants (ECs) present a significant risk to both the ecological environment and human health. However, there is currently limited knowledge regarding the presence of ECs in leachate and the surrounding groundwater environment of landfills. The heterogeneity of aquifers introduces additional uncertainty into the transport of ECs, thereby impacting the accuracy of pollution risk prediction. In this study, the types and concentrations of ECs in the leachate and surrounding groundwater were firstly investigated in a typical landfill in northeastern China. Results show that 6 different ECs were detected in groundwater monitoring wells around the landfill, with concentrations ranging from 1.25-1471 ng/L, higher than most investigated landfills in China. Leachate contained 18 different ECs with concentrations ranging from 0.25-30414 ng/L. Based on the statistical characteristics of lithology reflected by borehole data, random lithology fields were generated and transformed into heterogeneity parameter fields using Markov chain analysis to facilitate the risk assessment of ECs. Following a simulation period of 100 years, it was observed that due to the low permeability of the aquifer, pollutants only spread up to 700 m northward. While pollution plumes may disperse towards residential areas, the probability of exposure to EC in these regions is minimal. Conversely, areas with high pollution risk are predominantly located on the eastern and northern sides of the landfill. This study contributes to a deeper understanding of the impact of landfills on surrounding groundwater environments, and our proposed pollution risk assessment model can serve as a valuable reference for controlling and treating ECs.

Smart Monitoring Method for Land-Based Sources of Marine Outfalls Based on an Improved YOLOv8 Model

Land-based sources of marine outfalls are a major source of marine pollution. The monitoring of land-based sources of marine outfalls is an important means for marine environmental protection and governance. Traditional on-site manual monitoring methods are inefficient, expensive, and constrained by geographic conditions. Satellite remote sensing spectral analysis methods can only identify pollutant plumes and are affected by discharge timing and cloud/fog interference. Therefore, we propose a smart monitoring method for land-based sources of marine outfalls based on an improved YOLOv8 model, using unmanned aerial vehicles (UAVs). This method can accurately identify and classify marine outfalls, offering high practical application value. Inspired by the sparse sampling method in compressed sensing, we incorporated a multi-scale dilated attention mechanism into the model and integrated dynamic snake convolutions into the C2f module. This approach enhanced the model’s detection capability for occluded and complex-feature targets while constraining the increase in computational load. Additionally, we proposed a new loss calculation method by combining Inner-IoU (Intersection over Union) and MPDIoU (IoU with Minimum Points Distance), which further improved the model’s regression speed and its ability to predict multi-scale targets. The final experimental results show that the improved model achieved an mAP50 (mean Average Precision at 50) of 87.0%, representing a 3.4% increase from the original model, effectively enabling the smart monitoring of land-based marine discharge outlets.

Modeling the dispersion of wastewater pollutants in Gaza's coastal waters

The disposal of sewage water in Gaza City has emerged as a significant issue with extensive environmental repercussions. This study seeks to investigate the pollution plume resulting from the discharge of untreated or partially treated sewage water through Gaza City's main outlet into the Mediterranean Sea. Additionally, it aims to predict scenarios for various design configurations of submerged outfalls with either single-port or multi-port diffusers and compare these scenarios against the Environmental Protection Agency (EPA) recreational water quality criteria. According to the EPA, the concentration of Enterococci bacteria at the edge of the mixing zone should not exceed 35 CFU/100 ml to minimize the adverse environmental impact on the marine ecosystem.CORMIX software was utilized as a modeling tool to simulate the dispersion and attenuation behavior of pollutants resulting from this process and to conduct a sensitivity analysis to optimize the design configuration of the sewage disposal system. The simulation considered the influence of ambient conditions (ambient velocity, wind, and seawater density), effluent characteristics (density, flow rate, pollutant concentration, and pollutant decay rate), outfall configuration, and sea bathymetry.Simulation results indicate that a single-port diffuser is unsuitable according to EPA recreation standards. Multi-port unidirectional diffusers, extending 490 m from the shore into the water, meet the required standards. To a lesser extent, the multi-port staged distributor also meets the standards and is more recommended for counter-current situations.

On-site monitoring and numerical simulation on groundwater flow and pollution plume evolution in a hexavalent-chromium contaminated site

Accurately ascertaining spatiotemporal distribution of pollution plume is critical for evaluating the effectiveness of remediation technologies and environmental risks associated with contaminated sites. This study concentrated on a typical Cr(VI) contaminated smelter being currently remediated using pump-and-treat (PAT) technology. Long-term on-site monitoring data revealed that two highly polluted regions with Cr(VI) concentrations of 162.9 mg/L and 234.5 mg/L existed within the contaminated site, corresponding to previous chromium slag yard and sewage treatment plant, respectively. The PAT technology showed significant removal performance in these highly polluted areas (>160 mg/L) after six months of pumping, ultimately achieving complete removal of the pollutants in these high-pollution areas. Numerical simulation results showed that although the current remediation scheme significantly reduced the Cr(VI) pollution degree, it did not effectively prevent the incursion of the pollution plume into the downstream residential area after 20 years. Additionally, an improved measure involving supplementary pumping wells was proposed, and its remediation effects were quantitatively evaluated. Results indicated that the environmental pollution risk of groundwater downstream could be effectively mitigated by adding pumping wells, resulting in a reduction of the pollution area by 20 % in the case of adding an internal well and 41 % with the addition of external wells after 20 years. The findings obtained in this study will provide an important reference and theoretical guidance for the reliability analysis and design improvement of the PAT remediation project.

High-Resolution WRF Modeling of Wind and Thermal Regimes with LCZ in Almaty, Kazakhstan

This study evaluates the effectiveness of the Weather Research and Forecasting (WRF) model in simulating high-resolution atmospheric conditions for Almaty, Kazakhstan, a city prone to stagnant winter air. While the previously used Bougeault and Lacarrere scheme for parameterizing the planetary boundary layer was applied in high-resolution modeling, the number of vertical levels was increased, and a detailed local climate zones (LCZs) map was included. Ground-based observations from meteorological stations and monitoring stations, remote sensing data, and radiosonde measurements are used to verify the model. Comparison results with ground-based observations show that the WRF model with the LCZ map provides a better representation of the wind and thermal regimes of Almaty compared to the three-class land use map, including in high resolution. A good correspondence of wind direction is demonstrated by comparing the modeling results with pollutant transport plumes recorded by remote sensing data. In addition, a good correlation was found between land surface temperature from satellite data and air temperature simulated by WRF with a resolution of 333 m. A comparison of simulated data and aerological measurements confirmed that downscaling did not have a significant impact on boundary layer calculations. Analysis of turbulent processes showed that the adopted model effectively describes the attenuation and dissipation of turbulent kinetic energy and reflects the typical diurnal variations of meteorological processes in the atmosphere of Almaty in the anticyclonic winter period. The results of high-resolution WRF modeling can form the basis for the development of a hybrid system capable of modeling atmospheric processes at the building level.

Integrated framework to assess soil potentially toxic element contamination through 3D pollution analysis in a typical mining city

Soil potentially toxic elements (PTEs) pollution of contaminated sites has become a global environmental issue. However, given that previous studies mostly focused on pollution assessment in surface soils, the current status and environmental risks of potentially toxic elements in deeper soils remain unclear. The present study aims to cognize distribution characteristics and spatial autocorrelation, pollution levels, and risk assessment in a stereoscopic environment for soil PTEs through 3D visualization techniques. Pollution levels were assessed in an integrated manner by combining the geoaccumulation index (Igeo), the integrated influence index of soil quality (IICQs), and potential ecological hazard index. Results showed that soil environment at the site was seriously threatened by PTEs, and Cu and Cd were ubiquitous and the predominant pollutants in the study area. The stratigraphic models and pollution plume simulation revealed that pollutants show a decreasing trend with the deepening of the soil layer. The ranking of contamination soil volume is as follows: Cu > Cd > Zn > As > Pb > Cr > Ni. According to the IICQs evaluation, this region was subject to multiple PTE contamination, with more than 60% of the area becoming seriously and highly polluted. In addition, the ecological hazard model revealed the existence of substantial ecological hazards in the soils of the site. The integrated potential ecological risk index (RI) indicated that 45.7%, 10.13%, and 4.15% of the stereoscopic areas were in considerable, high, and very high risks, respectively. The findings could be used as a theoretical reference for applying multiple methods to integrate evaluation through 3D visualization analysis in the assessment and remediation of PTE-contaminated soils.

Extreme ozone episodes in a major Mediterranean urban area

Abstract. This study analyses three extreme ozone (O3) episodes that occurred in Barcelona (NE Spain) during the summers of 2015, 2018, and 2019. These episodes exceeded the EU's hourly information threshold (180 µg m−3) for the first time since at least the year 2000, raising concerns due to Barcelona's large population. By employing experimental data and various modelling tools, our main objective is to elucidate the underlying phenomena of these recent O3 episodes and improve predictive capabilities. The findings indicate that the factors contributing to these occurrences are largely consistent across episodes. These factors, with estimated O3 contributions specified for particular instances, comprise (i) initial O3 accumulation in surrounding coastal areas; (ii) weekend occurrence, accompanied by the corresponding weekend effect (+15 µg m−3); and (iii) the prevalence of Tramontana meteorological conditions during above-normal temperatures, which (iv) force the convergence of multiregional polluted air masses to the city (+45–65 µg m−3). Major source areas include regions of southern France through the Gulf of Lion, the interior of the Mediterranean, and eastern Spanish coastal regions, including Barcelona's pollution plume. Some of these factors, which may manifest in the days preceding the episodes, are observable or can be anticipated. This study enhances understanding of the mechanisms driving extreme O3 episodes recently observed in Barcelona and provides valuable insights for prediction.

Green buffers near industrial plants, examples in Jefferson County TX

Green buffers between industrial plants and residential areas have multiple purposes in mitigating air pollution and protecting the environment. This study focuses on providing information on examples of green space development by industries near residential areas in Jefferson County, Texas. One represents a full buffer where residences were totally removed, another is a partial buffer where some residences were removed in a neighborhood and the third represents vegetation of a formerly industrial facility. Additional estimates on benefits of buffer spaces with respect to a pollutant plume are also considered. The study used geospatial and property data from 1966 to 2020. The transition from a residential area to a full or partial buffers highlights possible mitigation of air pollution impacts while serving additional functions, such as boosting stormwater infiltration and improving the aesthetic attractiveness of the area. The transformation from oil tanks to forested space may display the potential for environmental remediation, but not all spaces are suitable for fully forested buffers, as safety and other limitations should be considered. With the analysis of the classic Plume Equation insights can be provided regarding the possible impact of green buffers on ground-level pollutant concentrations. The calculations for atmospheric stability classes A-F and for various stack heights provide an understanding of how different conditions may affect the pollutant concentrations. The presence of a green buffer can play a crucial role in controlling ground-level pollution concentrations and reduce a community’s perception of risk.

Geometry, Extent, and Chemistry of Fermentative Hot Spots in Municipal Waste Souk Sebt Landfill, Ouled Nemma, Beni Mellal, Morocco

The presence of fermentative hotspots in municipal waste dumps has been reported for several decades, but no study has focused on their size and shape. The uncontrolled landfill of Soub Sekt, covering an area of about 8 hectares in the Tadla plain in Morocco, is the source of a permanent pollution plume in the groundwater, detected by self-potential (SP) measurements. The study aims to detect and characterize these hotspots as well as the leachates that form within them. These hotspots are typically circular and smaller than 3 m in size, and they are concentrated within recent waste deposits. Intense electron transfer activities, particularly during redox reactions leading to metal solubilization, result in very low SP values (down to −60 mV), facilitating their detection. Several successive field campaigns suggest that they are active for 2–3 weeks. Due to the low permeability of the soils, highly mineralized leachates (average Electrical Conductivity 45 mS cm−1) rich in organic ions accumulate on the soil surface at the base of the waste windrows. There, they evolve by concentration due to evaporation and oxidation due to slow diffusion of atmospheric O2. Despite the small size of the hotspots generating the leachates, the accumulation of leachates in ponds and the low soil permeability limits the percolation rate, resulting in moderate but permanent groundwater pollution.

Cooperative Deep Reinforcement Learning for Dynamic Pollution Plume Monitoring Using a Drone Fleet

Cooperative Deep Reinforcement Learning for Dynamic Pollution Plume Monitoring Using a Drone Fleet

Domestic sewage dispersion scenarios as a subsidy to the design of urban sewage systems in the Lower Amazon River, Amapá, Brazil.

The final in natura discharge of urban domestic sewage in rivers in the Amazon is a widespread practice. In addition, there is an evident lack of knowledge about the self-depurative characteristics of the receiving water bodies in these rivers. This problem is a challenge for designing sanitary sewage system (SSS) projects in the region. We aimed to numerically simulate hydrodynamic scenarios to study pollutant dispersion processes in an urban stretch impacted by domestic sewage in the Lower Amazon River (Amapá, Brazil) using a hydrodynamic model calibrated and coupled to a dispersive model (Lagrangian) (SisBaHiA). The following methodological steps were performed: (a) bathymetric and liquid discharge experimental campaigns using acoustic techniques (acoustic doppler current profiler-ADCP); (b) identification of point and diffuse sources of pollution in the Santana Channel (CSA) and North Channel of the Amazon River (NCM) in Macapá; (c) calibration of the hydrodynamic model and simulation of the dispersive process of domestic sewage plumes; (d) simulation of dispersive process scenarios in two seasonal hydrological periods and different tidal phases. The results of the simulations indicated significant spatiotemporal variations in the plumes, suggesting critical restriction of water quality in the dry period. The hotspot water collection supply station for ETA-CAESA was found to be the most threatened site by diffuse and point source loads. The simulated impacts showed that concentration variation worsens seasonally, restricting the multiple uses of water in both seasonal periods, regardless of tide phase. The pollutant plumes near the coastal-urban zone were apparently more inhibited by the influence of currents, and, due to the greater dilution capacity in the center of the channel, by the effect reversing with the approximation to the riverbank. The research hypotheses were supported: (a) the process of self-depuration of pollutants in the NCM has considerable limitations in shallow areas, and (b) SSS design projects in the region of the Amazon estuarine complex require hydrodynamic and strict water quality assessment, especially when their hydrological-seasonal and bathymetric characteristics are significantly unfavorable to dispersive processes. Thus, a hydrodynamic analysis should be the primary criterion in designing any SSS projects in this stretch of the estuarine Amazon region.

Neglected flow direction detection in landfill water cycle: Precise characterization of leachate distribution through joint inversion of electrical resistivity and self-potential data

The leakage of leachate is a crucial but often overlooked hydrological process in the landfill water cycle. The concealed leakage of leachate not only leads to soil and groundwater pollution in surrounding areas but also affects the distribution of water and the metabolism of organic matter within the landfill. To accurately quantify this concealed hydrological process, we propose a method for detecting leachate leakage based on joint inversion of multi-source geophysical exploration data. By integrating multiple geophysical exploration data (resistivity and self-potential information), we reconcile the spatial differences in different exploration data to improve the accuracy of leachate and its pollution plume imaging. Additionally, we introduce an efficient alternating iteration technique within the joint inversion framework to ensure convergence of separately inverted models toward similar spatial structures. Simulation results indicate that: (1) for the early detection of small-scale high-concentration leachate pollution, the proposed confidence-induced joint inversion framework (CI-JIF) improves precision by 15.6 % compared to separate inversions. (2) for the detection of leachate long-term diffusion, CI-JIF accurately delineates the distribution of widespread high-concentration leachate, improving precision by 17.4 % compared to separate inversions. Further on-site experiments demonstrate that CI-JIF can more accurately reconstruct the distribution of leachate.

Combined effects of aquifer heterogeneity and subsurface dam on nitrate contamination in coastal aquifers

Subsurface dams are effective for seawater intrusion mitigation, yet they can cause upstream nitrate accumulation. This research examines the interplay between subsurface dam construction and aquifer layering on nitrate pollution in coastal settings, employing numerical models to simulate density-driven flow and reactive transport. The study reveals that while subsurface dams are adept at curbing seawater intrusion, they inadvertently broaden the nitrate accumulation zone, especially when a low-K layer is present. Heterogeneous aquifers see more pronounced nitrate accumulation from subsurface dams. This effect is pronounced as it influences dissolved organic carbon dynamics, with a notable retreat inland correlating with the expansion of the nitrate pollution plume. A critical finding is that controlling seawater intrusion via dam height adjustment within the Effective Damming Region effectively reduces nitrate levels and bolsters freshwater output. However, exceeding the critical threshold—where the dam surpasses the low-K layer's bottom—results in a substantial shift in nitrate concentration, underscoring the need for precise dam height calibration to avoid aggravating nitrate pollution. This study's innovative contribution lies in its quantification of the nuanced effects of subsurface dams in stratified aquifers, providing an empirical basis for dam design that considers the layered complexities of coastal aquifers. The insights offer a valuable framework for managing nitrate contamination, thus informing sustainable coastal groundwater management and protection strategies.

Stratified migration and distribution of the constituents of coal tar in the stratum

Coal tar (CT) is widely used in the rubber industry to produce a reinforcing substance known as carbon black. Due to the complexity constituents of CT, the migratory dynamics of its constituents have not been characterized, resulting in contamination of soil and groundwater. To understand the migration and distribution characteristics of different nature components of CT in the study site, the distribution and migration patterns of total petroleum hydrocarbons (TPHs), polycyclic aromatic hydrocarbons (PAHs), and Dense Non-Aqueous Phase Liquids (DNAPLs, ρ≫1 g/cm³) in soil and groundwater in a rubber enterprise were characterized and analyzed. We found that: the different components in CT settle at different points in the soil as they migrate, exhibiting stratification. Specifically, TPHs in soil and groundwater are mainly concentrated in the shallow layer near the tank area, and the maximum concentration is 113,000 mg/kg; PAHs are more migratory than TPHs, and the maximum concentration of PAHs is 7408 mg/kg. Most PAHs are concentrated in the middle layer and above; DNAPLs tend to be transported to deeper stratum, penetrating deeper into the terrain and aggregating into pools (depth＞13 m). In addition, the inherently slow flow of groundwater slower groundwater flow does not significantly impact the further migration of pooled DNAPLs, but it does influence the orientation of their pollution plume. This study provides a more accurate characterization of the dynamics of pollutants associated with rubber enterprises; these results bring forth a theoretical basis for the remediation and management of pollution linked with CT.

A new two-step particle tracking and channels model method for preferential 3-D flow and transport in large DFNs of fractured aquifers

A new two-step method has been developed for predicting three-dimensional (3-D) pollutant plumes and breakthrough curves (BTC) in fractured aquifers. Predicting fluid motion fields and pollutant concentrations in groundwater is a challenging task, due to the difficulties in building a 3-D discrete fracture network (DFN) with the same geometry of fractures and interconnections as in the studied aquifer and the computational complexity of the problem being modeled. To improve the representation of DFN, geological characterization of fracture apertures was performed using field well-pumping data as the prerequisite for the modeling approach. The modeling was performed in two steps: first, 3-D particle tracking following streamline (PTFS) simulations in DFN backbones, and second, a 3-D channels model (CM) analytical solution. The PTFS simulations captured the mean properties of the 3-D velocity field relevant to spatial and temporal transport along preferential flow pathways of a fractured aquifer. The 3-D CM solution yielded the exact BTC of concentrations accounting for the slowest flow pathways typically excluded from DFN backbones extraction methods. The PTFS/CM simulations were initially performed at the lab scale on a 3-D 20 m rock block from the Bari (South Italy) fractured aquifer. Results were consistent with the chlorophyll-A BTC obtained from a well-to-well tracer experiment. Subsequently, the capability of the new method was tested by increasing the scale of simulations to a larger 3-D DFN of 200 m with 2,200 fractures. The resultant BTC was obtained in 32 min, showing the proposed PTFS/CM technique can rapidly determine complex 3-D solutions in heterogeneous fracture-dominated aquifers. The applied Lagrangian and Eulerian techniques can provide quasi-deterministic BTCs and 3-D maps of pollutant concentrations, avoiding extensive computations required for conforming mesh methods. Moreover, the solution does not require multiple randomly arranged DFN realizations, as in particle tracking-based stochastic methods. These results have significant implications in modeling transport at the aquifer scale, where DFNs are composed of thousands of fractures.