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At the Gowanus Canal Superfund site in Brooklyn, New York, a multilayer reactive capping system is required as part of the approved remedy. The base reactive layer is an organoclay (OC)–sand layer containing a minimum of 25% by dry weight OC that is intended to block any upwelling mobile nonaqueous phase liquids (NAPLs). The construction quality assurance (CQA) method for verifying the OC content of the OC–sand stockpiles prior to placement in the canal consists of Loss on Ignition (LOI) testing performed at an offsite laboratory with a turnaround time of 3 days. To mitigate construction delays, rapid field testing methods to verify the OC content of the OC–sand blends were sought. Interestingly, electrical conductivity (EC) measurements on the as-is (not sieved or pulverized) OC, sand, and their blends provided several correlations with goodness of fit (R2) values >0.95 for a variety of sand-sized materials including: a commercial playground sand, beach sand, a limestone quarry sourced sand, and the sediment capping sand from the first Remedial Target Area (RTA-1) at the Gowanus Canal. The correlation curves and R2 values were relatively insensitive to change in the sand borrow source (silicate or karst geology or salinity). EC measurements were available in as little as 30 min and up to approximately 24 h using a tabletop pH/EC probe, distilled water, beaker, and magnetic stirrer. The EC approach and preliminary correlations presented here can greatly reduce CQA testing turnaround times to within hours (not days) in field settings. Lastly, similar findings were made when another commercially modified bentonite clay known as Fluorosorb-400™ was blended with playground sand. [ABSTRACT FROM AUTHOR]

The fate of light non-aqueous phase liquids (LNAPLs) is significantly influenced by complex characteristics of actual soils in unsaturated zone. To systematically analyze the multiphase migration process of LNAPLs in such soils, a two-dimensional laboratory device was designed to conduct benzene injection and water leaching experiments in three soil types of silty loam, loam and sandy loam that collected from a chemical industrial park in China. In the unsaturated zone, the jagged and asymmetric edges of pollution halo were observed attributed to heterogeneity in the small pores of the sampled soils. Additionally, low permeability also resulted in a high horizontal-to-vertical ratio of above 2.2. Based on laboratory experiments, a numerical model was established to simulate multiphase fluid migration, volatilization, dissolution and adsorption processes. The measured values closely matched the simulated values. The simulation results indicated that that over 99% of benzene was entrapped, with less than 1% volatilizing during the benzene injection stage in the unsaturated zone. During the leaching process, a portion of the benzene dissolved with the water flow, accounting for 1.557–4.786%. Compared to volatilization, dissolution played a more significant role in mass transfer processes. Combined with the laboratory experiments and numerical models, this conclusion elucidates the mechanism of multiphase distribution of LNAPLs in actual sampled soils. These findings provide a theoretical basis for developing reasonable and effective remediation methods for actual contaminated sites. [ABSTRACT FROM AUTHOR]

HVO has been noted as a more sustainable fuel, not only leading to lower total CO2 emissions, but also resulting in lower emissions of toxic substances upon fuel burning. The environmental impact of HVO and HVO diesel blends when accidentally spilled into the soil and ground water has, however, received little attention. While HVO and diesel exhibit nearly identical viscosity and density, their behavior in soils differs due to varying water solubility and fuel additives. In laboratory- and pilot-scale soil columns and lysimeters, we compared the migration and biostimulation-enhanced degradation of HVO, HVO-diesel blend (HVO15), and fossil diesel over 120 days. Additionally, we investigated the impact of fuel additives on migration by comparing HVO without additives to HVO15 and diesel in wet and dry soil columns over 21 days. Notably, HVO migrated through soil more rapidly and in greater quantities than diesel. In wet soil, 69% of added HVO, 8.4% of HVO15, and 21% of diesel leached through as light non-aqueous phase liquid (LNAPL). Dry soil showed smaller differences in fuel migration, but HVO did not mobilize when water was added, unlike HVO15 and diesel. Biostimulation reduced HVO leaching by 15% more than HVO15 and 48% more than diesel. Overall, HVO's behavior in soil differs significantly from fossil diesel, with factors like lower water solubility, reduced mobilization from dry soil, and higher in situ degradability contributing to its reduced environmental risk compared to fossil fuel alternatives in accident scenarios. [ABSTRACT FROM AUTHOR]

Groundwater LNAPL (Light Non-Aqueous Phase Liquid) contamination source identification (GLCSI) is essential for effective remediation and risk assessment. Addressing the GLCSI problem often involves numerous repetitive forward simulations, which are computationally expensive and time-consuming. Establishing a surrogate model for the simulation model is an effective way to overcome this challenge. However, how to obtain high-quality samples for training the surrogate model and which method should be used to develop the surrogate model with higher accuracy remain important questions to explore. To this end, this paper innovatively adopted the quasi-Monte Carlo (QMC) method to sample from the prior space of unknown variables. Then, this paper established a variety of individual machine learning surrogate models, respectively, and screened three with higher training accuracy among them as the base-learning models (BLMs). The Stacking ensemble framework was utilized to integrate the three BLMs to establish the ensemble surrogate model for the groundwater LNAPL multiphase flow numerical simulation model. Finally, a hypothetical case of groundwater LNAPL contamination was designed. After evaluating the accuracy of the Stacking ensemble surrogate model, the differential evolution Markov chain (DE-MC) algorithm was applied to jointly identify information on groundwater LNAPL contamination source and key hydrogeological parameters. The results of this study demonstrated the following: (1) Employing the QMC method to sample from the prior space resulted in more uniformly distributed and representative samples, which improved the quality of the training data. (2) The developed Stacking ensemble surrogate model had a higher accuracy than any individual surrogate model, with an average R2 of 0.995, and reduced the computational burden by 99.56% compared to the inversion process based on the simulation model. (3) The application of the DE-MC algorithm effectively solved the GLCSI problem, and the mean relative error of the identification results of unknown variables was less than 5%. [ABSTRACT FROM AUTHOR]

Sediment toxicity tests have applications in ecological risk and chemical safety assessments. Despite the many years of experience in testing and the availability of standard protocols, sediment toxicity testing remains challenging with very hydrophobic organic chemicals (VHOCs; i.e., chemicals with a log octanol/water partition coefficient of more than 6). The challenges primarily relate to the chemicals' low aqueous solubilities and slow kinetics, due to which several experimental artifacts may occur. To investigate the potential artifacts, experiments were performed, focusing on spiking and equilibrating (aging) sediments, as well as exposure quantification with passive sampling. The results demonstrated that generally applied, Organisation for Economic Co‐operation and Development–recommended spiking (coating) methods may lead to significant chemical losses and the formation of nondissolved, nonbioavailable VHOCs. Direct spiking appeared to be the most optimal, provided that intensive mixing was applied simultaneously. Passive dosing was tested as a novel way of spiking liquid VHOCs, but the approach proved unsuccessful. Intensive postspiking mixing during sediment equilibration for 1 to 2 weeks was shown to be essential for producing a homogeneous system, minimizing the presence of nondissolved chemical (crystals or nonaqueous phase liquids; NAPLs), and creating a stable toxicological response in subsequent toxicity tests. Finally, exposure quantification of VHOCs in sediments through passive sampling was found to be feasible with different polymers, although prolonged equilibration times may be required, and determining sampler/water partition coefficients can be extremely challenging. The results of additional experiments, focusing on toxicity test exposure duration, concentrations above which NAPLs will occur, and ways to distinguish actual toxicity from false‐positive results, are presented in Part 2 of this publication series. Environ Toxicol Chem 2024;43:1717–1727. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Surfactant-Enhanced Remediation is increasingly being recognized for its exceptional effectiveness in eliminating non-aqueous phase liquids in soil. A comprehensive knowledge of the technique is essential for its field application. This paper provides a thorough examination of Surfactant-Enhanced Remediation incorporating insights based on the most recent advancements. Firstly, the fundamental process and major mechanisms that underpin the technology were summarized, including mobilization, solubilizing, and emulsifying. Secondly, the improvements achieved by using surfactants in soil remediation, through chemical, physical, and biological methods, have been elucidated through theoretical explanations and practical case studies. Thirdly, the risks and other limitations of Surfactant-Enhanced Remediation were discussed with an outlook for future development. This review aims to promote understanding of the effectiveness and risks holistically in field implementation of the technique. [ABSTRACT FROM AUTHOR]

Research on the migration behaviors of contaminants in the aquitard has been deficient for an extended period. Clay is commonly employed as an impermeable layer or barrier to stop the migration of contaminants. However, under certain conditions, the clay layer may exhibit permeability to water, thereby allowing contaminants to infiltrate and potentially contaminate adjacent aquifers. Consequently, it holds immense importance to scrutinize and investigate the migration characteristics of light non-aqueous phase liquid (LNAPL) within the aquitard for the purposes of groundwater pollution control and remediation. To evaluate the environmental risk posed by organic contaminants in the aquitard, an experimental model was formulated and devised to monitor the LNAPL concentration in the aquitard under pumping conditions. The correlation between pumping rate and LNAPL concentration was investigated. A self-developed plexiglass sandbox model was used to simulate the migration characteristics of LNAPL in the aquitard under pumping conditions. Four experimental scenarios were designed, varying pumping rates, aquitard thicknesses, and groundwater level changes. The LNAPL concentration curve was derived by systematically tracking and analyzing LNAPL levels at various locations within the aquitard. The results indicated that higher pumping rates corresponded to increased migration of LNAPL, resulting in greater LNAPL ingress into the pumping well during extraction. A thicker aquitard demonstrated a more pronounced inhibitory effect on LNAPL, leading to an extended penetration time of LNAPL within the aquitard. The drawdown within the aquitard exerted a discernible influence on LNAPL migration, with the LNAPL concentration continuing to decrease in tandem with declining water levels during pumping. These research findings can establish a scientific foundation for the control and remediation of contaminants within aquitards. [ABSTRACT FROM AUTHOR]

Groundwater contamination caused by hydrocarbons is a common issue worldwide. Determining the volume of light non-aqueous phase liquids (LNAPL) that contaminate the subsurface environment is crucial for planning effective groundwater and soil remediation strategies, as well as determining the remediation endpoint. However, accurate approaches for quantifying the LNAPL volume in subsurface environments are scarce. To address this gap, we developed and tested a novel approach to quantify the volume of oil phase filling the soil pores. Our approach involves using a high-resolution technique, the laser induced fluorescence (LIF), to identify the presence of the oil phase, which was then correlated to total petroleum hydrocarbons (TPH) quantifications. For that, first, we obtained an empirical model to estimate the TPH present in the soil using fluorescence intensity and then, we converted the fluorescence intensity data in each log to equivalent TPH values. We used the model block approach, commonly used for ore resource estimation, to compute and discretize the volume of the aquifer contaminated by LNAPL into a set of blocks using the LIF data. Each block was assigned a mean TPH mass, which we used as a proxy for the LNAPL mass in the block. By summing the LNAPL mass in all blocks, we estimated the total LNAPL volume/mass in the investigated site. Our approach provides a simple and effective way to determine the amount of LNAPL contaminating the soil and groundwater, offering a new perspective for investigating hydrocarbon-contaminated sites. [ABSTRACT FROM AUTHOR]

Soil–water cocontamination with heavy metals and nonaqueous phase liquids (NAPLs) raises widespread concerns. Coexisting NAPL pollutants like toluene can antagonize the chemical processes employed for removing target heavy metals. This study investigates the impact of toluene on Cr(VI) adsorption by pumice-supported nano zerovalent iron (P-nZVI). The experiment was performed by passing a 10 mg/L Cr(VI) aqueous solution through a fixed-bed column in two batches, one without and the other with toluene. Results showed that toluene's copresence caused a 71.3% drop (3.14 to 0.9 mg/g) in P-nZVI adsorption capacity for Cr(VI). In toluene's absence, a Cr(VI) concentration in the effluent appeared after 60 h, while in its copresence, a Cr(VI) concentration appeared within 10 h. The average Cr(VI) concentration of the effluent increased from 5.05 mg/L in the first batch to 8.64 mg/L in the second batch. Breakthrough curve modeling demonstrated that the Thomas model best described the adsorption kinetics for the first case (R2 = 0.999), followed by the Yoon and Nelson and the Clark models with R2 = 0.996 and 0.994, respectively. Under toluene cocontamination, both the Thomas and the Yoon and Nelson models showed the best fit (R2 = 0.996). The inverse numerical analysis determined adsorption isotherm parameters (Ks , β, η) and confirmed that the reaction followed Langmuir behavior (β ≃ 1) with slight linearity under individual Cr(VI) presence. The results from this adsorption study, supported by adsorbent characterization before and after the reaction, demonstrated the unfavorable effects of coexisting contaminants on the removal of contaminants of concern. [ABSTRACT FROM AUTHOR]

This document is a short autobiography by Rien van Genuchten, who received the 2023 Wolf Prize in agriculture for his work on water flow and contaminant transport in soils. Van Genuchten discusses his upbringing on a family farm in the Netherlands, his education in mathematics and tropical agriculture, and his research in soil physics and vadose zone hydrology at New Mexico State University and Princeton University. He describes his contributions to the field, including the development of mathematical models and analytical functions to describe unsaturated soil hydraulic properties. The text also covers the author's collaborations, international research experiences, and concerns about environmental issues and climate change. [Extracted from the article]

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This study provides a comprehensive characterization of various hydrothermal systems in Southern Peru ranging from the faulted Precordillera's steep topography up to the volcanic High Cordillera (>4,000 m asl). The objective is to investigate thermal anomalies that may potentially serve as new geothermal resources. Our integrated approach combines: (a) geochemistry from 14 hot springs sampled throughout the Tacna region, and (b) 3D numerical modeling of coupled groundwater and heat transfer considering topography and faults embedded in homogeneous permeability. Water and gas analysis indicates that the springs located near volcanoes discharge Na‐K‐Cl waters with high temperatures (>87°C), high Total Dissolved Solid concentrations (TDS >3,452 mg/L), and free gases dominated by CO2 (>90 vol%). Springs located along the regional faults in the Precordillera discharge Ca‐SO4 and Na‐K‐Cl waters with moderate temperatures (27–53°C), intermediate TDS concentrations (464–2,458 mg/L), radiocarbon ages between 1.4 and 7.9 kyr, and free gases dominated by N2 (>95 vol%). The Aruma springs, which are located at the transition between the High and the Precordillera, display intermediate characteristics. Numerical models accurately replicate the locations and temperatures of the fault‐related springs only for permeable faults (>10−14 m2), revealing the creation of 100‐km long thermal plumes along faults, locally rising up the 150°C‐isotherm to about ∼1,000 m below the surface. This approach clearly distinguishes the spring origins, which are volcanic in High Cordillera and tectonic in Precordillera. Moreover, we highlight that steep topographic gradient and permeable reverse faults in the Andean forearc may generate considerable thermal anomalies, opening perspectives for the geothermal exploration. Plain Language Summary: Geothermal energy is an essential part of the transition to green energies. It consists of using the Earth' natural heat to generate electricity or provide direct heating. In the Peruvian Andes there is significant geothermal potential near volcanoes that constitute an efficient heat source. However, these are distant from many of the population hubs, mostly located along the Pacific Coast. In the Tacna region, Southern Peru, we observe hot springs aligned along faults near the city. We hypothesize that these faults act as pipes for the hot fluids making them suitable for geothermal energy extraction. The geochemical compositions of various hot springs in the region are compared with 3D numerical models simulating hydrothermal flows. We found that springs along volcanoes and those along faults have different geochemical signatures, evidencing different subsurface pathways. Numerical models accurately replicate the positions and temperatures of the observed and sampled hot springs and reveal significant thermal anomalies around compressional faults. Our findings open up promising perspectives for the geothermal exploration in the Andean forearc. Key Points: The geochemical properties of Southern Peru's hot springs are influenced by their spatial correlation with volcanic or tectonic featuresBy combining permeable faults and topography, 3D hydrothermal modeling replicates the temperatures and locations of observed springsDetection of regional topography‐driven thermal plumes along faults in the Andean forearc opens perspectives for geothermal exploration [ABSTRACT FROM AUTHOR]

The book "Hazard Hydrogeology" is a comprehensive resource that explores the correlation between hydrogeology and environmental geological hazards. It covers topics such as loess landslides, land subsidence, earth fissures, karst collapse, mine water inrush, and groundwater contamination in karst aquifers. The book provides in-depth analysis, case studies, and techniques for studying, evaluating, forecasting, and mitigating hydrogeological hazards. It is suitable for professionals and academics in the fields of hydrogeology, engineering geology, environmental geology, and environmental science. [Extracted from the article]

Leakages from fuel tanks and fuel transport pipelines are common occurrences that affect the environment and the geotechnical properties of geomaterials, which is of significant relevance in the case of unstable soils. In this work, experimental and numerical analyses were conducted to study the effect of kerosene on the mechanical behavior of collapsible soils. The compressibility tests on undisturbed loess samples were performed at natural water content, flooded with water, and flooded with a nonaqueous phase liquid (NAPL), such as kerosene. Numerical models were developed to reproduce and analyze the experimental results. The results show that the extended basic Barcelona model (EBBM) can successfully represent the stress–strain behavior of the soil under zero-lateral displacement conditions, as well as the higher compressibility developed by the specimens flooded with water than with kerosene. The presence of kerosene on tested loess produced negligible changes in swelling indexes and was not able to trigger collapse. The effect of particle–fluid interaction on the obtained results is discussed and analyzed to identify the main responsible mechanisms for soil collapse. [ABSTRACT FROM AUTHOR]

Accurate identification of groundwater contamination sources is important for designing efficacious site remediation strategies. Currently, the methods for identifying contamination sources mainly fall into three distinct categories: simulation optimization, Bayesian inference, and data assimilation. Each method has its own advantages and disadvantages under specific site conditions. To evaluate the applicability of these methods, we chose one representative inversion algorithm from each category, namely the Improved Butterfly Optimization Algorithm (IBOA) for simulation optimization, the Ensemble Smoother with Multiple Data Assimilation (ES‐MDA) for data assimilation, and the DiffeRential Evolution Adaptive Metropolis with a Snooker Update and Sampling from a Past Archive (DREAM(ZS)) for Bayesian inference. We conducted a comprehensive evaluation of these methods' performance under different model complexities, employing a surrogate model as a substitute for the complex forward model. By addressing two distinct problems involving conservative pollutant transport and Light Non‐Aqueous Phase Liquid (LNAPL) transport with biodegradation, we employed four criteria (elapsed time, result accuracy, posterior probability distribution, and noise resistance) for evaluation. The findings unequivocally indicate that DREAM(ZS) outperforms others in terms of result accuracy and posterior probability distribution. It also adeptly navigates the interrelations among disparate unknown variables. The strength of ES‐MDA lies in its efficiency. It achieves relatively satisfactory results with a reduced computational burden. In contrast, IBOA underperforms in both test problems. In terms of resistance to noise, both DREAM(ZS) and ES‐MDA perform better than IBOA does. Key Points: Hyperparameter optimization improves the accuracy of shallow learning surrogate models, making them comparable to deep learning modelsThree mainstream inversion methods were compared in elapsed time, result accuracy, posterior probability distribution and noise resistanceData assimilation and Bayesian inference methods are recommended for groundwater contamination source identification [ABSTRACT FROM AUTHOR]

Natural source zone depletion (NSZD) is the main process of LNAPL (Light Non-Aqueous Phase Liquid) removal under natural conditions. The NSZD rates assessed ranged from 0.55 to 11.55 kg·m−2·a−1 (kilograms per square meter per year) in previous studies. However, most of these data were obtained from sandy sites, with few clayey sites. To gain knowledge of NSZD in clayey soil sites, the study assessed the NSZD of a petroleum hydrocarbon-contaminated clayey soil site in China, combining the concentration gradient method with metagenomic sequencing technology. The results show that the abundance of methane-producing key enzyme mcrA gene in the source zone was more abundant than in background areas, which suggests that there was methanogenesis, the key process of NSZD. The concentration gradients of oxygen and carbon dioxide existed only in shallow soil (<0.7 m), which suggests that there was a thin methane oxidation zone in the shallow zone. The calculated NSZD rates range from 0.23 to 1.15 kg·m−2·a−1, which fall within the moderate range compared to previous NSZD sites. This study expands the knowledge of NSZD in clayey soil and enriches the attenuation rate data for contaminated sites, which is of significant importance in managing petroleum contaminants. [ABSTRACT FROM AUTHOR]

Active remediation at sites with light non‐aqueous phase liquid (LNAPL) often leaves residual hydrocarbons in the subsurface, necessitating long‐term management. While much of the effort in recent years has focused on natural source zone depletion (NSZD) as the primary method for demonstrating continued hydrocarbon removal, the same data collection methods can quantify biodegradation enhancements that can sustainably increase the rate of SZD. This approach has been applied at the Guadalupe Restoration Project, one of the first sites at which NSZD measurements and monitoring technology were demonstrated. Sitewide NSZD quantification was conducted using CO2 efflux measurements and subsurface temperature profiling. The results fell within the range of previously reported estimates that were based on soil‐gas profiling in the early 2000s, demonstrating the viability of the new methods at this site. The data collection methods were then deployed during pilot testing of solar‐powered bioventing. The system used seven 400‐W solar panels to power a regenerative blower that delivered approximately 0.85 cubic meter per minute (30 cfm) air to the LNAPL‐impacted vadose soil near the interface with the groundwater table. Soil‐gas data indicated an upward fanning of injected air toward ground surface. Elevated temperature due to hydrocarbon oxidation yielded an approximate 10.2 kg day−1 source depletion rate above the baseline NSZD mass removal rate over an approximate 30 m (100 ft) radius of influence, which aligned well with a 8.2 kg day−1 rate estimated from CO2 efflux measurements. Introduction of O2 via bioventing substantially increased the LNAPL biodegradation rate from baseline NSZD processes by almost an order of magnitude. The results demonstrate that site management can proceed along a sequenced program that began with aggressive hydraulic recovery of hydrocarbon product, transitions to enhanced SZD in areas with poorly recoverable LNAPL, and then to NSZD without intervention to address residual LNAPL across the full footprint of the LNAPL bodies. [ABSTRACT FROM AUTHOR]

Contamination of groundwater by harmful substances poses significant risks to both drinking water sources and aquatic ecosystems, making it a critical environmental concern. Most on-land spill events release organic molecules known as light non-aqueous phase liquids (LNAPLs), which then seep into the ground. Due to their low density and organic composition, they tend to float as they reach the water table. LNAPLs encompass a wide range of non-aqueous phase liquids, including various petroleum products, and can, over time, develop carcinogenic chemicals in water. However, due to frequent changes in hydraulic head, the confinement may fail to contain them, causing them to extend outward. When it contaminates water wells, people cannot reliably consume the water. The removal of dangerous contaminants from groundwater aquifers is made more challenging by LNAPLs. It is imperative to analyze the mechanisms governing LNAPL migration. As a response to this need and the associated dispersion of contaminants into adjacent aquifers, we have conducted a comprehensive qualitative literature review encompassing the years 2000–2022. Groundwater variability, soil structure, and precipitation have been identified as the three primary influential factors, ranked in the following order of significance. The rate of migration is shown to rise dramatically in response to changes in groundwater levels. Different saturation zones and confinement have a major effect on the lateral migration velocity. When the various saturation zones reach a balance, LNAPLs will stop moving. Although higher confinement slows the rate of lateral migration, it speeds up vertical migration. Beyond this, the lateral or vertical movement is also influenced by differences in the permeability of soil strata. Reduced mobility and tighter containment are the outcomes of migrating through fine-grained, low-porosity sand. The gaseous and liquid phases of LNAPLs move more quickly through coarse-grained soils. Due to the complexities and uncertainties associated with LNAPL behavior, accurately foreseeing the future spread of LNAPLs can be challenging. Although studies have utilized modeling techniques to simulate and predict LNAPL migration, the inherent complexities and uncertainties in the subsurface environment make it difficult to precisely predict the extent of LNAPL spread in the future. The granular soil structure considerably affects the porosity and pore pressure. [ABSTRACT FROM AUTHOR]

Bioventing is an established technique extensively employed in the remediation of soil contaminated with petroleum hydrocarbons. In this study, the objective was to develop an improved foundational bioventing model that characterizes gas flow in vadose zones where aqueous and non-aqueous phase liquid (NAPL) are present and immobile, accounting for interphase mass transfer and first order biodegradation kinetics. By incorporating a correlation for the biodegradation rate constant, which is a function of soil properties including initial population of petroleum degrader microorganisms in soil, sand content, clay content, water content, and soil organic matter content, this model offers the ability to integrate a specific biodegradation rate constant tailored to the soil properties for each site. The governing equations were solved using the finite volume method in OpenFOAM employing the "porousMultiphaseFoam v2107" (PMF) toolbox. The equation describing gas flow in unsaturated soil was solved using a mixed pressure-saturation method, where calculated values were employed to solve the component transport equations. Calibration was done against a set of experimental data for a meso-scale reactor considering contaminant volatilization rate as the pre-calibration parameter and the mass transfer coefficient between aqueous and NAPL phase as the main calibration parameter. The calibrated model then was validated by simulating a large-scale reactor. The modelling results showed an error of 2.9% for calibrated case and 4.7% error for validation case which present the fitness to the experimental data, proving that the enhanced bioventing model holds the potential to improve predictions of bioventing and facilitate the development of efficient strategies to remediate soil contaminated with petroleum hydrocarbons. [ABSTRACT FROM AUTHOR]

Results are reported from the third phase of an extensive Natural Source Zone Depletion (NSZD) research project with NSZD measurements at 12 locations with up to four years of monitoring using two measurement technologies: Carbon Traps and the temperature based, Thermal NSZD technology. Additionally, location-specific site characterization data was compiled to evaluate factors impacting NSZD rates. The two methods both resulted in site wide average NSZD rates in the low hundreds of gallons of light non-aqueous phase liquid (LNAPL) biodegraded per acre per year (gal/acre/year): 280 gal/acre/year for Thermal NSZD measurements and 360 gal/acre/year for Carbon Trap measurements. Based on the temporal and spatial variability in the NSZD data, these values were considered to be relatively consistent. In addition, these data support the case that NSZD is actively removing LNAPL at this site. Annual temporal rates generally varied by a factor of about two during the two- to four-year monitoring period, and the spatial distribution of NSZD rates across the site for the two methods ranged from 80 to 890 gal/acre/year. While the site-wide NSZD rates were relatively consistent, the location-specific Carbon Trap and Thermal NSZD data only had a weak correlation with a linear regression r2 of 0.4. The correlation between the spatial distribution of the NSZD rates and nine specific lithological, concentration, LNAPL distribution, and LNAPL composition factors showed strong correlations with only two of the factors: (1) a positive correlation to the fraction of LNAPL in the saturated zone as indicated by a rapid optical screening tool (ROST); and (2) a negative correlation to locations with significant clay in the geologic boring log. Overall, these results confirmed the observations from other NSZD field studies that showed significant temporal, spatial, and methodological variation in the NSZD rates at LNAPL sites. More importantly, these results support the conclusion that NSZD is active even for submerged LNAPL. [ABSTRACT FROM AUTHOR]

To effectively delineate the spatial distribution of oil contaminant plumes, geophysical methods indirectly measure the physical properties of the subsurface and can provide spatial information and images on a large scale, as opposed to traditional direct methods such as borehole drilling, sampling, and chemical analysis, which are time-consuming and costly. However, interpreting geophysical responses over non-aqueous phase liquid (NAPL)–contaminated sites is not straightforward due to inconsistent responses from biodegraded oil contaminants. In this study, we performed multi-geophysical surveys including seismic refraction, ground-penetrating radar, electrical resistivity tomography (ERT), and induced polarization (IP) surveys, to locate NAPL-contaminated zones in a clay-rich site. To reduce ambiguity in discriminating between oil contaminants and clay layers, we first figure out the geological structure of the site by interpreting geophysical data incorporating with borehole data. The ERT data highlighted the heavily contaminated regions in the unsaturated zone but were less distinctive below groundwater levels. Conversely, IP responses revealed potential hotspots within the clay layers, extending beneath the groundwater. Considering the 3D geological model, NAPL-contaminated zones are properly delineated through interpretation of ERT and IP data together with borehole data, and the contaminant source zone was properly estimated within the site. [ABSTRACT FROM AUTHOR]

In the frame of a collaboration between the Italian National Research Council (CNR) and Mares s.r.l., a study, about the possibility of determining radon vertical distribution at different soil depths in order to trace light non-aqueous phase liquid (LNAPL) contaminations, was developed. The radon deficit technique, based on the preferential solubility of soil gas radon into non-polar fluids, such as refined hydrocarbons, has been investigated by various theoretical and applied research so far. According to international scientific literature, radon deficit can be used both for geochemical prospection of the spatial irregular NAPL dispersion and for monitoring of remediation activities. Even though it is well known that this type of pollutants can be distributed along the vertical soil profile—firstly due to their density in comparison to water density, and secondly due to fluctuations of shallow aquifers, soil pore size, aging of contamination, and so on—the vertical localization of the plume still represents a scientific challenge. In this article, a method to determine the radon vertical profile is tested and applied to assess the potential use of the radon deficit technique in the vertical detection of pollutant presence for the first time in a fuelling station. Two LNAPL-contaminated sites were selected for a pilot test. Experimental findings seem to support the use of vertical radon geochemical prospection to delimit the depth range of a LNAPL pollution directly. Systematic data collection and modeling may lead to a 3D reconstruction of the dispersion of contaminant in different soil levels. [ABSTRACT FROM AUTHOR]

Most of the contaminant conceptual models in weathered crystalline bedrock aquifers in Brazil rely on data collected using conventional site investigation methods, at insufficient spatial resolution for associating contaminant distributions with observed heterogeneity. The DFN methodology was adapted for the characterization of a chlorinated solvent contaminated weathered crystalline bedrock aquifer, located in the region of the Jurubatuba district, Sao Paulo city, Brazil. The objective of this research is to establish a detailed 1-D conceptual model to show variable contaminant distribution within the bedrock matrix under different fracture and weathering conditions. The numerous depth-discrete rock sample analyses, assigned to specific geologic features, indicate the presence of PCE-Dense Non-Aqueous Phase Liquid (DNAPL) at discrete-depth intervals along the profile. These zones are mainly related to the lithological contacts and interfaces among the weathered bedrock. The soft and hard weathered-bedrock transition zone does not indicate a sharp decrease in the contaminant mass retention within the bedrock matrix for the studied area. This indicates that contaminant mass storage in the bedrock remains beyond this drilling method-defined interface, which can potentially sustain dissolved VOC concentrations over time and maintain the continuous vertical mass flux into deeper parts of the aquifer. There is a demonstrated need for an appropriate characterization methodology including high-resolution soil coring and sampling to delineate contaminant distribution over crystalline weathered bedrock aquifers. This is a key assumption for the definition of appropriate remedial and groundwater management strategies. [ABSTRACT FROM AUTHOR]

Time-Lapse Ground Penetrating Radar (GPR) was employed to study used engine oil (UEO) contamination of sandy environment in laboratory setting. GPR is a near-surface geophysical method that uses electromagnetic field to provide image of the dielectric properties of earth materials to detect structures and changes in material properties within the subsurface. This research aimed to detect, monitor and map the migration of UEO contaminant in sand. The results of this study revealed that the migration of the UEO contamination in homogeneously laid sand is non-uniform. UEO plumes were identified as high amplitude signals with enhanced reflectivity. There was a progressive decrease in GPR signal amplitudes (reflection reduction) within the contaminated area of the tank with time. This decrease of GPR signal amplitudes was interpreted as caused by the evaporation of some portion of the UEO in the vadose zone as a result of temperature increase in time and also due to the occurrence of UEO biodegradation. The time-lapse GPR proved to be an effective technique for detecting, monitoring, and mapping UEO migration within sand tank in laboratory setting. [ABSTRACT FROM AUTHOR]

The Biere #1‐22 oil production well near Poplar, Montana leaked brine and light nonaqueous phase liquid (LNAPL) to the shallow alluvial aquifer for several years before final closure in 2002. Since 2008, 2.5 billion L of brine have been removed (~90% of the original Cl mass). However, Cl will not reach the original background levels due to the reservoir of solutes entrained in the Bearpaw bedrock remnant from the lateral dense aqueous phase liquid flow across the alluvial/bedrock interface. After removal of ~100,000 L of product since 2006, residual LNAPL is now confined to 2.2 ha (5.5 acres) a decrease from the original 2.7 ha (6.6 acres) areal extent by 17%. The initial ~7.5 m thick product in 2002 is stable at a maximum of ~1 m. However, LNAPL has infiltrated into fine‐grained clay/silt units forming a smear zone in lenses 10 to 20 m bgs. Ongoing remediation has successfully mitigated benzene groundwater impacts over the last 14 years, with the benzene plume area having decreased by >99% (at the 5 μg/L) level from the maximum ~140 ha in 2002. This appears to be the first study evaluating the challenges to remediate a mixed LNAPL/dissolved organic/inorganic plume. Based on the mass removal to date, the asymptotic trends in solute concentrations, unpotable background groundwater quality, absence of a source/receptor pathway, lack of beneficial groundwater use, duration of mitigation with no obvious future accrual in benefit and the availability of institutional controls, it seems that the remedial strategies employed since 2006 have met their cost/benefit goals. [ABSTRACT FROM AUTHOR]

Per‐ and polyfluoroalkyl substances (PFAS) and weathered petroleum hydrocarbons can be co‐contaminants at sites where aqueous film‐forming foam (AFFF) was used to extinguish high‐temperature petroleum fires. Here, we report on the partitioning of six PFAS between water and a weathered diesel and gasoline range hydrocarbon light non‐aqueous phase liquid (LNAPL) collected from the subsurface of a decommissioned refinery. Results showed that both the structural features of PFAS and the characteristics of LNAPL exhibited significant impacts on the magnitude of PFAS partitioned to the LNAPL. The LNAPL–water partition coefficients (Kl) of PFOA and PFOS to the weathered LNAPL measured in this work were nearly or more than 10 times greater than Kl values calculated by others for partitioning to single‐component, unweathered NAPLs, indicating that laboratory studies evaluating LNAPL–water partitioning studies using single component NAPLs can largely underestimate the Kl expected to be encountered at contaminated AFFF sites. Interactions with LNAPL can be important controllers of PFAS fate and transport, and the Kl values estimated in this work suggest that LNAPL could be a significant transport sink for PFAS in the field. Results from this work suggest that PFAS partitioning to weathered LNAPL is an important process to be considered when designing remedial strategies, particularly those incorporating monitored natural attenuation or natural source zone depletion. [ABSTRACT FROM AUTHOR]

Low temperature thermal treatment (LTTT) is a technology that can enhance aqueous‐phase degradation reactions for organic constituents in groundwater. Understanding heat transfer in groundwater is important for the design of LTTT applications. In this study, the effect of permeability heterogeneity on temperature distributions during and after the application of heat was investigated by numerical modeling. An enhanced reaction zone was determined for the hydrolysis of 1,1,1‐trichloroethane (1,1,1‐TCA) using an average half‐life considering the temperature history during and after heating. For hydrolysis reactions, the average half‐life could be reduced substantially by reaching a high temperature for a short period of time because their reaction rates increase exponentially with increased temperatures. Results showed that the enhanced reaction zone was shifted downstream of the heater well zone at high groundwater velocities. This suggests that heaters should be shifted upstream of the target treatment zone to fully utilize the applied heat. In addition, permeability heterogeneity leads to greater macroscopic dispersion at higher velocities. This resulted in higher spreading of heat and faster heat dissipation in the simulations with a heterogeneous permeability condition compared with a homogenous permeability condition. As a result, the enhanced reaction zone was smaller in simulations with higher levels of permeability heterogeneity at a mean velocity of 0.3 m/day. [ABSTRACT FROM AUTHOR]

At the Gowanus Canal Superfund site in Brooklyn, New York, layers comprising different granular activated carbon (GAC)/sand blends are being placed as part of a multilayer reactive capping system required for the approved remedy. Depending on the capping zone, the targeted GAC contents can vary from 6% to 60% by dry weight (%). The construction quality assurance (CQA) method for verifying the GAC content of each GAC/sand stockpile consists of loss on ignition (LOI) testing performed at an offsite laboratory with a turnaround time of 3 days. To mitigate construction delays and site congestion at the upland blending site, rapid field (onsite) testing methods to verify the GAC content of the GAC/sand blends were sought. Portable X-ray fluorescence (pXRF) was successfully used on oven dried and crushed GAC/sand materials to develop three linear elemental [calcium (Ca), silicon (Si), and sulfur (S)] correlations with goodness of fit (R2) values greater than 0.95 for Ca and S. Sulfur was not detected in the sand and appeared linked to the bituminous coal source materials for manufacturing the GAC and thus became the primary element to track the GAC content. The measured GAC contents of the CQA samples by pXRF were within 2 to 3 percentage points of the values determined by LOI testing and were obtained onsite within hours. In addition, the pXRF measurements more closely matched the initially batched materials on site that were intentionally overdosed by up to 25% of the GAC blending target to avoid failure. The preliminary correlation presented here provides strong promise for the use of pXRF as the CQA method to furnish accurate GAC content results for the GAC/sand blends onsite within hours (not days) during the implementation of the Gowanus Canal capping remedy. [ABSTRACT FROM AUTHOR]

An extensive treatability study was completed on a chlorobenzene-rich nonaqueous phase liquid (CB-NAPL) impacted source zone at an active industrial site. A baseline leaching condition for the low permeability silty site soils was established via one-dimensional (1D) semidynamic leach testing on undisturbed and remolded core samples using EPA 1315 modified (M) [Method 1315 – mass transfer rates of constituents in monolithic and compacted granular material using a semidynamic tank leaching procedure, revision 1. Washington, DC: EPA. Office of Resource Conservation and Recovery] for use with hydrocarbons under zero headspace conditions in a new, specially designed apparatus. Comparison of the most heavily impacted samples (average of 2,932 to 9,422 mg/kg CB) indicated that the EPA 1315M 1D leaching response was typically within a factor of two when comparing undisturbed versus remolded (homogenized) samples. Even though soil homogenization may have changed the initial soil fabric and contaminant distribution, the comparable outcomes suggested that it may be sufficiently accurate to work with remolded samples given the many challenges and uncertainties associated with undisturbed cores. In addition, CB leaching rates were observed to be more closely associated with total CB content than hydraulic conductivity (K) for samples characterized by K < 1 × 10−6 cm/s. This is perhaps not surprising since the concentration gradient is the key driver for mass transfer in diffusion-controlled media. Comparison of the EPA 1315M leaching results from an untreated, undisturbed silty soil layer from the hotspot location to the leaching results of a stabilization/solidification (S/S)-treated soil homogenized over the full treatment depth showed CB percent leaching reductions (%LRs) of approximately 85.5% for the contract-specified laboratory-based mix design and 74.5% for a field quality assurance (QA) sample taken during remedial construction. These %LR values for the S/S treatment were considerably lower than the calculated %LR of >99% using EPA 1316M on the most heavily impacted sand sample from the hotspot location. This discrepancy in perceived performance prompted a discussion on the appropriate use and limitations of the %LR framework for assessing S/S performance and stressed the importance of properly designating the principal threat waste condition as that hotspot location/interval characterized by the greatest contaminant mobility. [ABSTRACT FROM AUTHOR]

A better understanding of the distribution of nonaqueous phase liquid (NAPL) plumes is of great importance to groundwater pollution remediation and control. However, the efficiency of surrogate models in simulating the transport is still not well addressed. Selecting a leakage problem as an example, 50 sets of random permeability distributions are generated using the Monte Carlo method, and a numerical model is used to obtain benchmark data of NAPL transport. Four machine learning methods are employed to simulate dense NAPL transport under point leakage sources across spatiotemporal scales. The validation of the models demonstrate that the random forest model can also effectively capture the spatial-temporal distribution of the plume in heterogeneous aquifers, with a maximum mean absolute error and root mean square error smaller than 5.55 x 10-4 and 5.88 10-5, respectively. Meanwhile, the multiple phase outcome from the random forest model fits well with the numerical results under the scenarios of linear leakage sources and light NAPL transport. The total time consumed in the computation is reduced by over 150 times after using the surrogate models. The results suggest that surrogate models can provide a prom)ising way to understand NAPL transport in heterogeneous aquifers [ABSTRACT FROM AUTHOR]

Featured Application: Radon deficit reveals the presence of residual NAPL(Non-Aqueous Phase Liquid) contamination in soil and groundwater, giving a good picture of their vertical and spatial location. A combined and repeated approach consisting of measurements of radon and NAPL concentration coupled with groundwater table dynamics makes it possible to assess the evolution of the contamination phenomena. The application ofexploratory factor and principal component analyses to this dataset provides a key to understanding the attenuation processes, whether natural or induced, by the application of mitigation practices, and delivers models (conceptual and mathematical) to manage the site reclamation. Soil and groundwater contamination by NAPLs (Non-Aqueous Phase Liquids) is certainly a big issue for protecting the environment. In situ clean-up actions are routinely applied to mitigate the risk and are supplemented by monitoring surveys to assess the degree, extension, and evolution of the contamination. Radon gas is here used as a tracer of contamination because of its high solubility in non-polar solvents that produce a reduced concentration of the gas in polluted soil and groundwater with reference to radon levels in adjacent "clean" areas. This approach was employed in two sites where gasoline and diesel spillage occurred, causing soil and groundwater contamination. The two case studies were chosen because of their difference in terms of the hydrogeological features, age of the spillage, composition of residual NAPLs, and clean-up measures to test the advantages and limits of this approach in a variety of settings. Radon data, NAPL concentration in the groundwater (mainly total hydrocarbons, Methyl Tertiary-Butyl Ether and Ethyl Tertiary-Butyl Ether) and the depth of the groundwater table were periodically collected in surveys that spanned a period of two years. This dataset was statistically processed using principal component analysis to unravel which factors and attenuation processes are working in the sites and the response of the radon deficit approach to this complex series of phenomena concurrently occurring there. [ABSTRACT FROM AUTHOR]

In this study, zeolite and bentonite were used as the base materials to prepare barrier. Through mechanics experiment, penetration experiment, microscopic characterization, adsorption experiment, centrifuge model experiment and numerical simulation experiment, the control effect of barrier on ammonia nitrogen pollution in manganese slag storage yard was discussed. The results showed that the optimal mass ratio of zeolite and bentonite was 3:2, and the mass of cement accounted for 50% of the mass ratio of the whole system. The addition of zeolite improved the anti-penetrability performance and mechanical properties of the barrier material, the minimum hydraulic conductivity reached 2.049x10-10 m/s, and the maximum compressive strength reached 3.36 MPa. The zeolite made the internal structure of the barrier material became uniform and dense, which significantly improved the adsorption capacity of the barrier material to ammonia nitrogen. The adsorption process of ammonia nitrogen by the barrier material was more consistent with the quasi-second-order kinetic model and the Freundlich model, and the adsorption process was endothermic. With the penetration of ammonia nitrogen solution, the hydraulic conductivity of barrier material gradually decreased and became stable. Visual MODFLOW numerical model was used to simulate the process of ammonia nitrogen migration in groundwater, and the barrier was still not penetrated after 5 000 d. The zeolite-bentonite barrier showed excellent effect in preventing and controlling ammonia nitrogen pollution in manganese slag yard. [ABSTRACT FROM AUTHOR]

Groundwater professionals require methods to estimate the potential time required to achieve remedial goals, including locations within and downgradient of zones containing nonaqueous phase liquids (NAPLs). NAPLs have long been recognized as persistent contaminant sources to groundwater. Dissolution of multicomponent NAPLs is particularly complex, and numerical models that explicitly simulate it are not widely available. This study introduces an equilibrium partitioning approximation to simulate the dissolution of the most soluble chemical components from multicomponent NAPL containing a significant fraction of relatively insoluble mass. The effective distribution coefficient that describes depletion of a specific compound from NAPL is estimated based on the properties of the NAPL and the porous medium. This study also presents numerical modeling results that support the utility of the method, with verification using published empirical data collected during dissolution of residual coal tar in a controlled laboratory sand tank experiment. The numerical modeling method uses equilibrium partitioning as an approximation and matched the concentrations of the two most soluble NAPL components in and downgradient of the NAPL zone with reasonable accuracy. The results suggest that the method should be useful for screening‐level assessments and can be adapted to compare relative groundwater restoration timeframes of select NAPL components for various remedial alternatives. [ABSTRACT FROM AUTHOR]

The reduction of nitric oxide (NO) emissions to atmosphere has been recently addressed using biological technologies. However, NO removal through bioprocesses is quite challenging due to the low solubility of NO in water. Therefore, the abatement of NO emissions might be improved by adding a chelating agent or a mass transfer vector (MTV) to increase the solubility of this pollutant into the aqueous phase where the bioprocess takes place. This research seeks to assess the performance of different non-aqueous phase liquids (NAPs): n-hexadecane (HEX), diethyl sebacate (DSE), 1,1,1,3,5,5,5-heptamethyl-trisiloxane (HTX), 2,2,4,4,6,8,8-heptamethylnonane (HNO), and high temperature silicone oil (SO) in chemical absorption–biological reduction (CABR) integrated systems. The results showed that HNO and HTX had the maximum gas-liquid mass transfer capacity, being 0.32 mol NO/kmol NAP and 0.29 mol NO/kmol NAP, respectively. When an aqueous phase was added to the system, the mass transfer gas–liquid of NO was increased, with HTX reaching a removal efficiency of 82 ± 3% NO with water, and 88 ± 6% with a phosphate buffer solution. All NAPs were tested for short-term toxicity assessment and resulted neither toxic nor inhibitory for the biological activity (denitrification). DSE was found to be biodegradable, which could limit its applicability in biological processes for gas treatment. Finally, in the CABR system tests, it was shown that NO elimination improved in a short time (30 min) when the three mass transfer vectors (HEX, HTX, HNO) were added to enriched denitrifying bacteria. [ABSTRACT FROM AUTHOR]

The mobilization, speciation, and transformation of these pollutants in the soil and groundwater ecosystem vary greatly depending on the specific hydro-biogeochemical processes and environments. To effectively address soil pollution sources and manage the risks of groundwater pollution, it is essential to comprehend how complex geological and hydrogeological factors in soil-groundwater systems interplay with climate change and human activities. The common types of organic pollutants in soil and groundwater environments include polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), chlorinated solvents, polychlorinated biphenyls (PCBs), pesticides, and other emerging contaminants [[5], [7]]. The delicate balance of our ecosystems is under threat from the unrelenting release of contaminants into the environment. [Extracted from the article]

Millions of contaminated sites worldwide need to be remediated to protect the environment and human health. Although numerous remediation technologies have been developed, selecting optimal technologies is challenging. Several multiple criteria decision-making methods for screening the optimal remediation technology have been proposed, but they mostly focus on a specific area rather than the whole contaminated site. In recent years, the "contamination source control—process blocking—in situ remediation" technology mix model has gradually gained high appreciation. Nevertheless, the screening of technologies within each chain of this model relies heavily on arbitrary personal experience. To avoid such arbitrariness, a petroleum-contaminated site containing light non-aqueous phase liquids (LNAPLs) was used as an example, and a scientific screening and combination procedure was developed in this study by considering the distribution characteristics of contaminants. Through the procedure, a technology mix, which includes institutional control, risk monitoring, emergency response, multiphase extraction, interception ditch, monitoring of natural attenuation, hydrodynamic control, as well as some alternative technologies, was found, aiming at different locations and strata. The clear spatial relationship concept promises to enhance the effectiveness of contaminated site remediation. The proposed method only gave us a technical framework and should be tested and enriched in future studies. [ABSTRACT FROM AUTHOR]

Many shallow ex-situ and in-situ remediation treatments come from the contamination of underground soils and groundwater sources by organic hydrocarbon components called non-aqueous phase liquids (NAPLs). These contaminants, if leaking, can impose long-term threats causing environmental and health concerns. One of the versatile in-situ remediation techniques is using surfactant/foam processes that can overcome subsurface heterogeneity and improve NAPL removal. Motivated by an earlier study of successful implementation of surfactant/foam in-situ remediation processes, this simulation study investigates the next phase of the research, that is, (i) understanding two different roles of foams during the treatment: foams for "mobility control" vs. foams for "blocking" and (ii) evaluating the potential of blocking foams by placing foams downstream (i.e., foam injected into the downstream extraction wells, but surfactant is still injected into the upstream injection wells). When twenty-four different scenarios are taken into consideration for the 23-days pilot test with 3 injection wells and 3 extraction wells, the results from the simulations reveal that using foams for blocking purpose is as efficient as, or more efficient than, foams for mobility-control purpose, exhibiting the oil recovery up to near 94.9%. Additional simulation efforts also show that foams as a blocking agent have a unique advantage over mobility-control foams because of less pressure buildup required and, therefore, less chance of displacing the contaminants out of the treatment area. This feasibility study of examining foams as a blocking agent focuses on vertical wells currently, which can be regarded as a stepping stone into the broader range of similar applications with horizontal wells located in hilly terrain. [ABSTRACT FROM AUTHOR]

This study increases the mass transfer of hydrophobic contaminants in a microbial fuel cell-based trickling filter (MFC/TF) by adding non-aqueous phase liquid. The removal efficiency, mineralization efficiency and elimination capacity of styrene are respectively increased by 1.56 times, 1.86 times and 1.52 times, the power density is increased by 2.6 times and the internal resistance is reduced by approximately 22% after adding 10% silicone oil to the MFC/TF. This is mainly attributed to a decrease in the internal resistance after adding silicone oil, which increases electron transfer on the surface of the auxiliary anode packing and increases the number of electricity-producing bacteria. Adding 10% silicone oil to the MFC/TF increases the number of degrading bacteria and electricity-generating bacteria in the MFC/TF by 2.3–2.5 times. The performance of the MFC/TF using 10% silicone oil is significantly increased because there is increased mass transfer of styrene in the MFC/TF and increased power generation. [Display omitted] [ABSTRACT FROM AUTHOR]

Accurate estimation of the nonaqueous phase liquids (NAPLs) saturation such as chlorinated organic compounds (COCs) in aquifers is crucial for the proper remediation of contaminated groundwater. A combination of conservative and partitioning tracers (PTs) are commonly used to assess NAPL saturations in the subsurface at COC release sites, using the partitioning interwell tracer test (PITT). In this study, five fluorescent dyes were assessed as PTs to estimate the saturation of octanol and 3 COC NAPLs in soil columns. PT experiments required an initial assessment of both partitioning (NAPL/water and octanol/water) and linear free‐energy relations. The predictability of the partition coefficients was correlated to the pH of the two‐phase fluids for both systems (NAPL/water and octanol/water). The COC NAPLs were acidic and some PTs with acid‐base properties, like fluorescein, are easily influenced by pH. The PITT experiments were performed in a column packed with glass beads, using rhodamine WT as PT because of its particular specificity for the complex mixture of NAPLs and sodium chloride as the inert tracer. Breakthrough curves of rhodamine WT were examined to estimate the saturation of a NAPL made of a complex mixture of COCs. The DNAPL residual saturation estimation accuracy was sensitive to both pH variations and the water velocity. The latter was represented by an exponential function which resulted from non‐equilibrium measurements, heterogeneous sweeping of the contaminated sample, and redistribution of the NAPL droplets in the medium. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Traditional soil mechanics idealizes geomaterials as being in a dry or fully water-saturated state. However, there is a zone between the ground surface and the groundwater table, where the soil is unsaturated, which means the pore space is filled with air and water. This zone is affected by environmental changes during wetting and drying seasons through precipitation, evaporation, or evapotranspiration. The influence of water content, for instance, the degree of saturation, on the characteristics of soil under dynamic loading i.e. at small to intermediate strains, for example, small-strain shear modulus (Gmax), modulus degradation [G(γ)], and damping ratio [D(γ)] remain of interest in the geotechnical community due to the practical relevance of the problem. This study attempted to cover the existing gaps in the dynamic characteristics of soil with different degrees of saturation. Therefore, Hostun sand (HS) was mixed with 30% Amberger kaolin (AK) and compacted to Proctor density at the optimum water content. They were saturated in a special saturation cell applying back pressure. Then, the saturated samples were dried to different degrees of saturation. Resonant column (RC) tests were carried out on the prepared samples to determine the effect of the degree of saturation on Gmax, G(γ), and D(γ). Of note, in this series of tests, suction was not strictly controlled; however, the necessary volume change corrections were performed via various noncontact transducers. To describe the experimental observations and to evaluate the impact of the degree of saturation on Gmax, G(γ), and D(γ), the soil water characteristic curve (SWCC) of the adopted mixture was determined. The results showed a significant increase of Gmax with the degree of saturation following an S-phaped curve. Based on the new data, previous models to predict Gmax were inspected under a significantly wider range of the degrees of saturation and suction. In addition, the effect of the degree of saturation on the intermediate strain characteristics of the adopted mixture [G(γ)/Gmax] and D(γ) was evaluated, where modulus degradation was found almost unaffected by Sr while a moderate increase of damping ratio with Sr was observed. [ABSTRACT FROM AUTHOR]

Climate and groundwater are always in a state of dynamic equilibrium. Subsurface systems contaminated by light non-aqueous phase liquid (LNAPL) present a challenge to understand the overall impact of water table dynamics, due to various interacting mechanisms, including volatilization, and LNAPL mobilization/dissolution along the groundwater flow direction and oscillating redox conditions. We investigated the impact of water table fluctuations on LNAPL natural attenuation and soil geochemical characteristics in semi-arid coastal areas under saline conditions. Four soil columns operated for 151 days under anoxic conditions where a layer of benzene and toluene were subjected to a stable and fluctuating water table associated with low and high salinity conditions. The bottom of stable and fluctuating columns reached an anaerobic state after 40 days, while the middle of stable column took 60 days. pH values of the fluctuating columns covered a wide range, and at the end shifted towards alkaline conditions, unlike the stable columns. In fluctuating columns, pore water sulfate decreased in the middle, but in stable columns, it decreased in the first 40 days, which suggested that sulfate was the primary electron donor and sulfate-reducing bacteria were present. At the source zone, benzene and toluene reached their maximum concentration after 30 and 10 days for the stable and the fluctuating columns, respectively. Significant decrease in benzene and toluene concentrations occurred under the fluctuating water table. Salinity did not affect benzene and toluene concentrations in the aqueous phase, although water table fluctuations have the most effect. Soil solid-phase analysis shows fluctuating columns have less toluene than stable columns. Solid-phase analysis showed the fluctuating columns have less benzene and toluene concentrations as compared to the stable columns. [ABSTRACT FROM AUTHOR]

Natural source zone depletion (NSZD) is increasingly being considered as a risk-management option at sites impacted with light non-aqueous phase liquids (LNAPLs). NSZD can be applied in isolation or in combination with active remediation techniques, depending on site-specific risk-management requirements. A case study of the transition from active remediation to passive NSZD is presented for a petroleum-impacted site in NW Europe. This transition was supported by multiple lines of evidence/management options, including: the introduction of institutional controls on groundwater and land-development restrictions; the results from a residual-NAPL risk assessment; monitoring to establish that the LNAPL plume is reducing in size; a LNAPL transmissivity assessment; a CO2 equivalent assessment of remediation options; and a LNAPL recovery diminishing returns model. Through application of local sustainable remediation principles consistent with ISO/SuRF-UK sustainable remediation frameworks and tools, regulatory approval was obtained for a partial closeout of the remediation system. By the final year of operation, NSZD rates in the portion of the site on which transition to NSZD has been agreed were over three times greater than active LNAPL recovery rates (12 000 l/ha/a for NSZD; 3800 l/ha/a for active LNAPL recovery). In the remaining active remediation areas total fluids extraction currently outperforms NSZD and will be continued until a comparable point is reached when NSZD removal exceeds active remediation. At that point transition to NSZD alone will be considered as the most sustainable risk-based approach. [ABSTRACT FROM AUTHOR]

Attaining control over the electrical conductivity of gallium nitride through impurity doping is one of the foremost achievements in semiconductor science. Yet, unwanted contaminants and point defects continue to limit device performance, and experimental techniques alone are insufficient for elucidating the behavior of these unintentionally incorporated species. Methodological advancements have made first-principles calculations more powerful than ever and capable of quantitative predictions, though care must still be taken in comparing results from theory and experiment. In this Tutorial, we explain the basic concepts that define the behavior of dopants, unintentional impurities, and point defects in GaN. We also describe how to interpret experimental results in the context of theoretical calculations and also discuss how the properties of defects and impurities vary in III-nitride alloys. Finally, we examine how the physics of defects and impurities in GaN is relevant for understanding other wide-bandgap semiconductor materials, such as the II–IV-nitrides, boron nitride, and the transition metal nitrides. [ABSTRACT FROM AUTHOR]

Metal–air batteries have higher theoretical specific energies than existing rechargeable batteries including Li-ion batteries. Among metal–air batteries, the Na–O2 battery has gained much attention due to its low discharge/charge overpotentials (∼100 mV) at relatively high current densities (0.2 mA/cm2), high electrical energy efficiency (90%), high theoretical energy density, and low cost. However, there is no information reported regarding the effect of CO2 contamination in non-aqueous Na–air batteries. Density functional theory has, here, been applied to study the effect of low concentrations of CO2 contamination on NaO2 and Na2O2 growth/depletion reaction pathways and overpotentials. This was done on step surfaces of discharge products in non-aqueous Na–air batteries. Adsorption energies of CO2 at various nucleation sites for both step surfaces were determined, and results revealed that CO2 preferentially binds at the step valley sites of (001) NaO2 and 1 1 ¯ 00 Na2O2 surfaces with binding energies of −0.65 eV and −2.67 eV, respectively. CO2 blocks the step nucleation site and influences the reaction pathways and overpotentials due to carbonate formation. The discharge electrochemical overpotential increases remarkably from 0.14 V to 0.30 V and from 0.69 V to 1.26 V for NaO2 and Na2O2 surfaces, respectively. CO2 contamination is thus drastically impeding the growth/depletion mechanism pathways and increases the overpotentials of the surface reaction mechanism, hampering the performance of the battery. Avoiding CO2 contamination from intake of gas and electrolyte decomposition is thus critical in development of Na–air batteries. [ABSTRACT FROM AUTHOR]

Microseismicity in subsurface geologic environments, such as sandstone gas reservoirs, is expected in the presence of liquid or gas injection. Although difficult to predict, the potential for microseismic events is important to field-scale projects, such as geologic storage of CO2, whereby the gas is injected into natural sandstone formations. We conjecture that a primary factor causing microseismicity is the existence of metastable states in a granular porous medium and provide experimental evidence for its validity. External perturbation triggers abrupt relaxation events which, with a certain probability, can grow into macroscopic microseismic events. Here, the triggering perturbation is produced by cooling to a cryogenic temperature. As the "sensor" for the abrupt relaxation events, we use thin Al films deposited on the sandstone surface. We show that as the temperature is varied, the films' resistance exhibits sharp jumps, which we attribute to mechanical restructuring or microfractures in the fabric of the sandstone. We checked the superconducting characteristics of the Al thin films on the sandstone and found microwave-induced Shapiro steps on the voltage–current diagrams. Such quantized steps provide indications that the film is made of a network of nanobridges, which makes it even more sensitive to abrupt relaxation events occurring in the substrate, i.e., in the underlying sandstone. [ABSTRACT FROM AUTHOR]

The article discusses the work of the Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP) in funding research and development for environmental restoration. The organizations focus on various program areas, including environmental restoration, and have been significant funders of applied groundwater research. The article highlights two presentations from a symposium on groundwater treatment and management. One presentation discusses the use of mass discharge as a regulatory metric for groundwater cleanup, while the other explores the use of phytoremediation and bioaugmentation as a green remediation strategy for 1,4-dioxane contamination. Additionally, the article mentions the development of web applications to simplify environmental data analysis and visualization. [Extracted from the article]

Mechanical properties of sandstone, such as compressive strength and young's modulus, are commonly used in the design of geotechnical structures and numerical simulation of underground reservoirs using models such as the digital groundwater, equivalent porous medium, and Discrete Fracture Network (DFN) models. A better understanding of the mechanical behaviors of sandstone under different loading conditions is imperative when assessing the stability of geotechnical structures. This paper highlights the effect of the physical properties (i.e., porosity, mean grain size) and environmental conditions (i.e., water content and confining stress) on uniaxial compressive strength, triaxial compressive strength, and young's modulus of sandstone. A series of uniaxial and triaxial compression experiments are conducted on sandstone formations from Wyoming. In addition, experimental data on sandstones from the literature are compiled and integrated into this study. Prediction equations for the compressive strengths and young's modulus of sandstone are established based on commonly available physical properties and known environmental conditions. The results show that the mean Uniaxial Compressive Strength (UCS) decreases as the porosity, water content, and mean grain size increase. Furthermore, a predictive empirical relationship for the triaxial compressive strength is established under different confinements and porosity. The relationship suggests that the mean peak compressive strength increases at a higher confinement and decreases at a higher porosity. The results and recommendations provide a useful framework for evaluating the strength and deformation of most sandstone. [ABSTRACT FROM AUTHOR]

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The effects of groundwater table fluctuation (GTF) on the remediation of a petrochemically polluted riverside using soil vapor extraction (SVE) were investigated. The migration and transformation of benzene, toluene, ethylbenzene, and o-xylene (BTEX) in cases of natural attenuation, SVE without GTF, and SVE with GTF were simulated using the TMVOC model. The results showed that the optimized extraction well pressure and influencing radius of the target site were 0.90 atm and 8 m, respectively. The removal rates of BTEX in cases of natural attenuation, SVE without GTF, and SVE with GTF were 11.49%, 85.16%, and 97.33%, respectively. The removal rate of BTEX was maximized in the case of SVE with a GTF amplitude of 0.5 m to 1 m. The removal rates of benzene (99.99%), toluene (99.74%), ethylbenzene (96.37%), and o-xylene (94.72%) were maximized in the case of SVE with GTF. For the cases of SVE without GTF and SVE with GTF, mass losses of BTEX in gaseous (0.05 kg, 0.05 kg, respectively) and aqueous phases (5.46 kg, 5.87 kg, respectively) were consistent. However, the mass loss of BTEX in the non-aqueous phase liquid (NAPL) phase in the case of SVE with GTF (155.13 kg) exceeded that in the case of SVE without GTF (135.41 kg). This is because GTF positively affected both the solubility and volatility of BTEX in the NAPL phase. With the groundwater table decreasing, flows of gas and gaseous pollutants increased by 25% along the vertical section. At this stage, the removal rates of volatile organic compounds can be further improved by increasing the flow of the extraction well. [ABSTRACT FROM AUTHOR]