Search Results (21)

The rapid expansion of the petrochemical industry has led to significant environmental issues, including groundwater and soil contamination from hydrocarbon spills. This study investigates the movement and dispersion of hydrocarbon contaminants in the Rey industrial area in Tehran (Iran) using a two-dimensional finite element model. The results indicate that the oil plume exhibits slow migration, primarily due to low soil permeability and high hydrocarbon viscosity, leading to localized contamination. High-density pollution zones, such as TORC and REY7, are characterized by persistent hydrocarbon accumulation with minimal lateral migration. The findings emphasize the limited effectiveness of natural attenuation alone, highlighting the need for targeted remediation measures in high-density zones to accelerate contamination reduction. This study provides insights into the dynamics of hydrocarbon pollution and supports the development of effective remediation strategies. Full article

The residual non-aqueous phase liquid (NAPL) within low-permeability lenses of aquifers is a major contributor to “tailing”, a phenomenon that complicates the remediation of NAPL-contaminated sites. A fundamental challenge in addressing this issue is the lack of understanding of the primary controlling factors and underlying effects of NAPL residuals in these aquifer lenses. This study aims to identify the key factors and mechanisms affecting NAPL residuals in low-permeability lenses through a series of experimental approaches. These include soil column simulation experiments on NAPL residuals in various low-permeability lenses, adsorption experiments on aquifer and lens particles, pore mercury intrusion testing, and particle size distribution analysis. The experiments provided valuable data on residual NAPL saturation S_R, particle adsorption capacity, particle size, gradation, and pore size and distribution in different lenses. Using a mass conservation approach, the particle adsorption contributed less than 0.5% to the total NAPL residuals, while retention accounted for more than 99.5%, highlighting that retention is the dominant mechanism governing NAPL persistence in these lenses. The mechanism underlying this result was further clarified through an analysis of particle size characteristics. Correlation analysis was conducted to examine the relationships between residual NAPL and macropore porosity (n_max, diameter > 60 μm), mesopore porosity (n_mid, diameter = 30~60 μm), and small pore porosity (n_min, diameter < 30 μm). The results demonstrated that mesopores exhibited the strongest correlation with NAPL retention, due to their pronounced capillary action and sufficient storage capacity for NAPL. Full article

Light non-aqueous phase liquids (LNAPLs), which include various petroleum products, are a significant source of groundwater contamination globally. Once introduced into the subsurface, these contaminants tend to accumulate in the vadose zone, causing chronic soil and water pollution. The vadose zone often contains lens-shaped bodies with diverse properties that can significantly influence the migration and distribution of LNAPLs. Understanding the interaction between LNAPLs and these lens-shaped bodies is crucial for developing effective environmental management and remediation strategies. Prior research has primarily focused on LNAPL behavior in homogeneous media, with less emphasis on the impact of heterogeneous conditions introduced by lens-shaped bodies. To investigate the impact of lens-shaped structures on the migration of LNAPLs and to assess the specific effects of different types of lens-shaped structures on the distribution characteristics of LNAPL migration, this study simulates the LNAPL leakage process using an indoor two-dimensional sandbox. Three distinct test groups were conducted: one with no lens-shaped aquifer, one with a low-permeability lens, and one with a high-permeability lens. This study employs a combination of oil front curve mapping and high-density resistivity imaging techniques to systematically evaluate how the presence of lens-shaped structures affects the migration behavior, distribution patterns, and corresponding resistivity anomalies of LNAPLs. The results indicate that the migration rate and distribution characteristics of LNAPLs are influenced by the presence of a lens in the gas band of the envelope. The maximum vertical migration distances of the LNAPL are as follows: high-permeability lens (45 cm), no lens-shaped aquifer (40 cm), and low-permeability lens (35 cm). Horizontally, the maximum migration distances of the LNAPL to the upper part of the lens body decreases in the order of low-permeability lens, high-permeability lens, and no lens-shaped aquifer. The low-permeability lens impedes the vertical migration of the LNAPL, significantly affecting its migration path. It creates a flow around effect, hindering the downward migration of the LNAPL. In contrast, the high-permeability lens has a weaker retention effect and creates preferential flow paths, promoting the downward migration of the LNAPL. Under conditions with no lens-shaped aquifer and a high-permeability lens, the region of positive resistivity change rate is symmetrical around the axis where the injection point is located. Future research should explore the impact of various LNAPL types, lens geometries, and water table fluctuations on migration patterns. Incorporating numerical simulations could provide deeper insights into the mechanisms controlling LNAPL migration in heterogeneous subsurface environments. Full article

Impermeability and water blocking are crucial for remediating shallow groundwater contamination. Traditional methods often employ curtain-grouting technology to create impermeable layers. However, cement slurry curing is irreversible, leading to permanent closure of underground aquifers and secondary pollution. This study employs an innovative approach by fabricating cylindrical models that simulate actual strata and utilizing a high-temperature and high-pressure displacement device. It systematically analyzes the variations in soil pore structure, distribution, porosity, and permeability under different temperatures, pressures, and freezing durations. The microscopic characteristics of the freezing process in water-bearing soils were studied. Results demonstrate that longer freezing time improves the effectiveness of soil freezing, reaching complete freezing at temperatures as low as −4 °C for samples with low water content. For water-saturated samples, freezing below −6 °C results in nearly zero porosity. Increased pressure at a certain freezing temperature significantly reduces permeability. When freezing temperature falls below −4 °C, water permeability in saturated samples after freezing reaches near-zero levels, while unsaturated samples experience complete freezing. These findings provide a theoretical foundation for constructing freezing curtains in remediating shallow groundwater pollution. Full article

Electrokinetic remediation (EKR) has shown great potential for the remediation of in situ contaminated soils. For heavy metal-contaminated soft clay with high moisture content and low permeability, an electrokinetic remediation method with electrolytes placed above the ground surface is used to avoid issues such as electrolyte leakage and secondary contamination that may arise from directly injecting electrolytes into the soil. In this context, using this novel experimental device, a set of citric acid (CA)-enhanced EKR tests were conducted to investigate the optimal design parameters for Cu- and Zn-contaminated soft clay. The average removal rates of heavy metals Cu and Zn in these tests were in the range of 27.9–85.5% and 63.9–83.5%, respectively. The results indicate that the Zn removal was efficient. This was determined by the migration intensity of the electro-osmotic flow, particularly the volume reduction of the anolyte. The main factors affecting the Cu removal efficiency in sequence were the effective electric potential of the contaminated soft clay and the electrolyte concentration. Designing experimental parameters based on these parameters will help remove Cu and Zn. Moreover, the shear strength of the contaminated soil was improved; however, the degree of improvement was limited. Low-concentration CA can effectively control the contact resistance between the anode and soil, the contact resistance between the cathode and soil, and the soil resistance by increasing the amount of electrolyte and the contact area between the electrolyte and soil. Full article

Increasing soil contamination with nickel (Ni) and copper (Cu) is a growing environmental concern, adversely affecting ecosystems and the survival of both plants and animals. This study investigated the morphological and physiological responses of Euphorbia marginata Pursh seedlings to varying concentrations of Ni and Cu over a 45-day period. The findings revealed that low concentrations of Ni and Cu enhanced morphological indexes, root indexes, biomass, and photosynthetic pigment content of E. marginata, while high concentrations inhibited these parameters. Compared to the control, Ni and Cu stresses induced membrane peroxidation, increased cell membrane permeability, and inhibited the synthesis of soluble proteins and proline in the leaves. The seedlings demonstrated an ability to mitigate Ni and Cu toxicity by increasing soluble sugar content and enhancing the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). Notably, E. marginata exhibited a higher capacity for Cu²⁺ enrichment and translocation compared to Ni²⁺. Combined Ni and Cu treatments reduced the maximum enrichment and translocation levels of both metals in E. marginata. This study highlights the superior tolerance of E. marginata to Ni and Cu stresses and elucidates the mechanisms underlying its response, providing a theoretical basis for the use of landscape plants in the remediation of heavy-metal-contaminated soils. Full article

Contaminants stored in low-permeability soils can continue to threaten the adjacent groundwater system even after the aquifer is considered remediated. The redistribution of contaminants from low-to-high-permeability aquifer zones (Back-Diffusion) can generate a long-term plume tail, commonly considered one of the main obstacles to effective groundwater remediation. In this paper, a laboratory test was performed to reproduce the redistribution process from low-permeability silt lenses (k ≈ 1 × 10⁻⁷ m/s) to high-permeability sand aquifers (k ≈ 1 × 10⁻³ m/s). The target of the experimental and numerical approach was finalized to verify what influence the shape and position of the lenses could have, with respect to the bulk flow, on the time necessary to complete the depletion of the dissolved substances present in the lenses. For this purpose, an image analysis procedure was used to estimate the diffusive flux of contaminants released by these low-permeability zones in different boundary conditions. The results obtained in the laboratory test were used to calibrate a numerical model implemented to simulate the Back-Diffusion process. Once calibrated, the numerical model was used to simulate further scenarios to evaluate the influence of the location and shape of the low-permeability lenses on the time necessary to diminish its contaminant content when subjected to a steady-state flow. The numerical model was also used to investigate the effect of different groundwater velocities on the depletion time of the process. The results show that the shape and position of the lens have an important impact on the time necessary to empty the lens, and an increase in the velocity field in the bulk medium (flow rate rising from 1.6 l/h to 2.5 l/h) does not correspond to diminishing total depletion times, as the process is mainly governed by diffusive transport inside the lens. This appears to be significant when the remediation approach relies on pumping technology. Future research will verify the behavior of the released plume in a strongly heterogeneous porous medium. Full article

Lead contamination in soil has emerged as a significant environmental concern. Recently, pulse electrochemical treatment (PECT) has garnered substantial attention as an effective method for mitigating lead ions in low-permeability soils. However, the impact of varying pulse time gradients, ranging from seconds to hours, under the same pulse duty cycle on lead removal efficiency (LRE) and energy consumption in PECT has not been thoroughly investigated. In this study, a novel, modified PECT method is proposed, which couples PECT with a permeable reaction barrier (PRB) and adds acetic acid to the catholyte. A comprehensive analysis of LRE and energy consumption is conducted by transforming pulse time. The results show that the LREs achieved in these experiments were as follows: PCb-3 s (89.5%), PCb-1 m (91%), PCb-30 m (92.9%), and PCb-6 h (91.9%). Importantly, these experiments resulted in significant reductions in energy consumption, with decreases of 68.5%, 64.9%, 51.8%, and 47.4% compared to constant voltage treatments, respectively. It was observed that LRE improved with an increase in both pulse duration and voltage gradient, albeit with a corresponding rise in energy consumption. The results also revealed that corn straw biochar as a PRB could enhance LRE by 6.1% while adsorbing migrating lead ions. Taken together, the present data highlights the potential of modified PECT technology for remediation of lead-contaminated soil, which provides an optimal approach to achieve high LRE while minimizing energy consumption. Full article

Zn is a toxic heavy metal that seriously endangers human health and ecological stability. For a long time, traditional remediation techniques have been used to remediate Zn-contaminated soil prone to other problems such as secondary contamination. In recent years, due to the great danger posed by Zn pollution, there has been an increasing interest in applying eco-friendly and sustainable methods to remediate Zn-contaminated soil. Therefore, in this study, microbially induced calcium carbonate precipitation (MICP) technology was used to bioremediate zinc ions by transforming ionic heavy metals into insoluble solid-phase minerals. Through the unconfined compressive strength (UCS) test, direct shear (DS) test, and penetration test (PT), the results showed that the unconfined compressive strength of the treated specimens increased by 187.2~550.5%, the cohesion increased significantly compared with the internal friction angle of specimens, and the permeability coefficient can be reduced by at least one order of magnitude. During the treatment of Zn pollutants, the mobility of heavy metal zinc ions was significantly reduced, the percentage of exchangeable state Zn content was significantly reduced, and the leaching concentration of zinc ions in Zn-contaminated soil was reduced to about 20 mg/L, which was significantly lower than the limit in the standard (100 mg/L). These results were further confirmed by scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, which indicated coprecipitation of calcium carbonate (CaCO₃) and ZnCO₃. The microbial solidification/stabilization of Zn-contaminated soil was most effective when the curing age of 28 d, the cementation solution concentration of 1 mol/L, and the cementation solution ratio of 1:2. Therefore, the bio-immobilization of zinc ions by MICP has the potential for application as a low-cost and eco-friendly method for heavy metal remediation. Full article

Based on the information from an actual petroleum-contaminated site, a one-dimensional soil column was used to examine the vertical transportation diversities of different petroleum components under the influence of water table fluctuations, and the results revealed the following: (1) There were two obvious pollution accumulation zones under the condition of water table fluctuations: (i) The pollution infiltration zone dominated by the residual phase was formed at the leakage position, and (ii) the floating zone dominated by the free phase was formed near the water table. Combined with the viscosity of the organic components, the concentrations of the residual phase were octanoic acid > hexadecane > cyclohexane > toluene. Compared to coarse sand, clay can adsorb more components. (2) Different fluctuation frequencies had a great influence on the migration process of components. The free phase can transfer into the residual phase during the low groundwater table fluctuation. In the case of high-frequency groundwater fluctuations, there were more free phase components that can be carried by the water flow. However, due to the continuous flushing by the water, pollutants were finally spread to the whole underground system. (3) A cost-effectiveness remediation strategy is based on the difference in pollutant transportation. Therefore, the conclusions in this paper are fully applied in the actual contaminated sites. Specifically, the air-sparing (AS) and soil vapor extraction (SVE) devices were installed in the vadose zone to remove volatile substances (such as toluene). The permeable reactive barriers (PRBs) were set in the groundwater fluctuation zone to repair the residual pollutants (alkanes, cyclane, and asphaltenes hydrocarbons) that are continuously converted from the residual phase to the dissolved phase and free phase due to water level fluctuations. Hence, the results of this study provided a specific, targeted, and comprehensive strategy for petroleum pollution treatment. Full article

Since the 1990s, sandstone-type uranium in the northern basin of China has become the main target for mining. Uranium mining can cause a series of impacts on the environment. A conceptual model of the geo-environment for sandstone-type uranium in northern China was described, which covers the changes in the geo-environmental characteristics in the natural state, in the mining process, during decommissioning and after treatment. Sandstone-type uranium is mainly distributed in the Songliao, Erlian, Ordos, Turpan–Hami and Ili Basins, which have arid climates and poor stratum permeability. Pitchblende is the main uranium-bearing mineral and is associated with iron, copper, coal, organic matter and other minerals. The mineral often has a low ore grade (0.01–1.0%) and high carbonate content (2–25%). Uranyl carbonate accounts for more than 90% of the total uranium in groundwater. The uranyl content is closely related to the TDS. The TDS of groundwater in the eastern and central ore belts is usually lower than 2 g/L, while in the western region, such as Xinjiang, it can exceed 10 g/L. In situ leaching (ISL) is the main mining method that results in groundwater pollution. Acid leaching leads to a pH decrease (<3), and heavy metals represented by U and Fe exceed the background values by hundreds of times, resulting in groundwater pollution. CO₂ leaching is more environmentally friendly, and the excess ions are usually Ca²⁺, Mg²⁺, NO₃⁻ and HCO₃⁻. Soil chemical anomalies originate mostly from wind erosion and precipitation leaching of decommissioned tailings. Uranium pollution is mainly concentrated within 20 cm of the surface, and the exceedance generally varies from two to 40 times. During ISL, a series of environmental measures will be taken to prevent pollution from being exposed to the surface. After treatment, the decommissioned uranium mines will likely have no impact on the surrounding environment. In the future, the protection of groundwater should be strengthened during production, and remediation methods based on electrokinetic, microbial and permeable reactive barrier (PRB) technology should be further researched. Full article

Cost-effective remediation is increasingly dependent on high-resolution site characterization (HRSC), which is supposed to be necessary prior to interventions. This paper aims to evaluate the use of low-flow purging and sampling water level data in estimating the horizontal hydraulic conductivity of soils. In a new quali-quantitative view, this procedure can provide much more information and knowledge about the site, reducing time and costs. In case of high heterogeneity along the well screen, the whole procedure, as well as the estimation method, could be less effective and rigorous, with related issues in the purging time. The result showed significant permeability weighted sampling, which could provide different results as the pump position changes along the well screen. The proposed study confirms this phenomenon with field data, demonstrating that the use of multiparameter well logs might be helpful in detecting the behaviour of low-permeability layers and their effects on purging and sampling. A lower correlation between low-flow permeability estimations and LeFranc test results was associated with high heterogeneity along the screen, with a longer purging time. In wells P43, MW08 and MW36, due to the presence of clay layers, results obtained differ for almost one order of magnitude and the purging time increases (by more than 16 min). However, with some precautions prior to the field work, the low-flow purging and sampling procedure could become more representative in a shorter time and provide important hydrogeological parameters such as hydraulic conductivity with many tests and high-resolution related results. Full article

Traditional electrokinetic (EK) technology can remove contaminants from soil, but the efficiency is generally low. This study reports on the combination of enhanced EK and a waste ferric hydroxide (Fe(OH)₃) permeable reactive barrier (PRB) for the remediation of soil in sulfide mine areas. Hydroxyethylene diphosphonic acid (HEDP) and FeCl₃ were used as a compound chelating agent. The experimental results showed that EK combined with PRB technology (95.32% Cd removal) was more effective than single EK in removing cadmium (Cd) from the contaminated soil, because of the compound chelating agent and PRB filled with sustainable Fe(OH)₃ adsorbent. Additionally, the application of PRB in combination with HEDP was able to increase the sulfate removal rate to 96.19%. The accumulated energy consumption of these two systems was 182.4 and 356 kWh/m³, respectively, after EK remediation using PRB. Full article

The objective of this study is to determine the impacts of expected climate change on slope stability. For this purpose, the case study of a slope instability, that was triggered in 2021 was selected. The stability analysis was performed considering the theory of rainfall infiltration and using Geo-Studio’s SEEP/W module for the surface infiltration model of the slope. A parametric stability analysis of the slope was conducted to determine the importance of climate change on slope stability. Conditions for changes in volumetric water content, water permeability, porewater pressure, and groundwater flow are important. When soil permeability is low, the factor of safety decreases during rainfall events and on the days following, while when permeability is higher, safety increases after rainfall events. The effect of lower cohesion is nearly linear, with the factor of safety decreasing by 0.1 for every 1 kPa less cohesion. The increase in net infiltration of water may be the most critical factor for slope instability. The results of the analysis indicate that timely reduction of water net infiltration through planting and proper surface water runoff from the upper road and slope would be a relatively simple and inexpensive measure compared to the cost of remediating the landslide, considering expected climate change. Therefore, it is advisable to analyze all slopes with respect to the expected climate change, taking into account the potential impacts of climate change. Full article

Electrokinetic (EK) remediation methods can remove heavy metals from the soil, but the removal efficiency is generally low. In this paper, indoor remediation experiments of simulated copper-contaminated clay under four different types of electrolyte conditions (KCl, HAc, AC, and PASP (polyaspartic acid)) are carried out to validate the theory of an electrodynamically coupled steel slag permeability reactive wall (PRB). By comparison with EK remediation, it has been shown that the EK-PRB coupled remediation method can promote the removal of heavy metal copper in the soil, especially in the removal of reducible copper and exchangeable copper. The method can effectively avoid the increase in soil pH value and reduce the accumulation range of heavy metals while reducing the accumulation amount of heavy metals. This method has better energy utilization efficiency, and the unit energy consumption is smaller than the single electric remediation test. Full article