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Dense Chlorinated Solvents and other DNAPLs in Groundwater
... This shows that even without the major isotope hypothesis, the assumption of equality between the 186 "classical" thermodynamic constant and the one of the reference isotopologue is relevant in this more complex 187 case too, providing a new and needed validation of this generally applied assumption. 188 Double substitution on two different elements 189 In this subsection we develop mathematical expressions for double substitution on two different elements. introducing isotopes are E 0 (E 0 0 , E 1 0 ) and E 1 (E 0 1 , E 1 1 ). ...
... Les solvants chlorés constituent un type de contamination organique très fréquent des eaux souterraines (sous forme dissoute ou en phase libre) notamment dans les pays industrialisés du fait de leur large utilisation par de nombreuses industries (industrie chimique, textile, électronique, aéronautique, automobile, ...) depuis la Seconde Guerre Mondiale [188]. De plus, ces contaminants présentent une toxicité élevée, étant cancérigènes et pouvant produire d'importants dégâts au sein d'organes vitaux comme le foie ou les reins [188], [211]. ...
... Les solvants chlorés constituent un type de contamination organique très fréquent des eaux souterraines (sous forme dissoute ou en phase libre) notamment dans les pays industrialisés du fait de leur large utilisation par de nombreuses industries (industrie chimique, textile, électronique, aéronautique, automobile, ...) depuis la Seconde Guerre Mondiale [188]. De plus, ces contaminants présentent une toxicité élevée, étant cancérigènes et pouvant produire d'importants dégâts au sein d'organes vitaux comme le foie ou les reins [188], [211]. Référence est souvent faite aux solvants organiques chlorés par les termes de liquides denses non aqueux (« dense non-aqueous phase liquids », DNAPLs), famille de substances à laquelle ils appartiennent. ...
L’éventail des processus géochimiques modélisés par les codes de transport réactif a vocation à s’élargir de plus en plus et permet à ces codes de traiter des problématiques de nature différente (stockage de déchets radioactifs, exploitation minière, pollutions, etc.). Cette dernière décennie a vu l’essor de la modélisation des fractionnements isotopiques par les codes de transport réactif. Cette fonctionnalité permet d’ajouter au suivi de réactions géochimiques leur impact sur la composition isotopique des espèces chimiques. Néanmoins, l’hypothèse classiquement utilisée lors de ces modélisations repose sur l’existence d’un isotope majoritaire au sein des isotopes de l’élément d’intérêt. Ces travaux menés à MINES ParisTech contiennent les développements mathématiques réalisés afin de vérifier que la méthodologie reste valide pour un ensemble d’hypothèses moins contraignantes, vérifiées dans la majorité des systèmes naturels. Plusieurs applications ont été réalisées avec Hytec, code de transport réactif développé à MINES ParisTech. La comparaison de résultats dans le cadre d’un benchmark a permis de valider l’emploi de cette méthodologie avec Hytec. Ensuite, un modèle de dégradation et de migration de solvants chlorés dans un système aquifère-aquitard a été mis au point et permet de simuler les signatures isotopiques du carbone et du chlore au sein de ces composés. Les résultats ont montré que le suivi de la composition isotopique des solvants dans l’aquifère peut renseigner sur leur potentielle dégradation dans l’aquitard. Par ailleurs, ces travaux montrent l’importance de la configuration du modèle numérique utilisé ainsi que le potentiel offert par la modélisation des fractionnements isotopiques combinée à la polyvalence d’Hytec.
... Tetrachloroethylene (also known as perchloroethylene, henceforth referred to as PCE) is a chlorinated solvent (a volatile organic compound, VOC) primarily used in dry cleaning and metal degreasing and exposure is highly suspected to cause cancer in humans (Guha et al., 2012;Barul et al., 2017). Chlorinated solvents are denser than water, and are often referred to as dense non-aqueous phase liquids (DNAPLs) and a common groundwater contaminant that typically form large plumes (up to several kilometers in length) when dissolved in flowing groundwater (Pankow and Cherry, 1996). Methods for estimating mass flux and discharge of VOCs from groundwater to surface water typically rely on some variation of control plane (i.e., cross section multi-level sampling orthogonal to the direction of groundwater flow), where plume discharge is defined as the amount of contaminant mass migrating through the control plane per unit of time (Pankow and Cherry., 1996;Guilbeault et al., 2005;Chapman et al., 2007). ...
... Chlorinated solvents are denser than water, and are often referred to as dense non-aqueous phase liquids (DNAPLs) and a common groundwater contaminant that typically form large plumes (up to several kilometers in length) when dissolved in flowing groundwater (Pankow and Cherry, 1996). Methods for estimating mass flux and discharge of VOCs from groundwater to surface water typically rely on some variation of control plane (i.e., cross section multi-level sampling orthogonal to the direction of groundwater flow), where plume discharge is defined as the amount of contaminant mass migrating through the control plane per unit of time (Pankow and Cherry., 1996;Guilbeault et al., 2005;Chapman et al., 2007). In a recent study, Nickels et al. (2023) used point-scale streambed measurements of hydraulic parameters and VOC concentration to quantify VOC discharge from groundwater to surface water in high detail at small scale. ...
Polluted groundwater discharge at a chlorinated solvent contaminated site in Hagfors, Sweden, is affecting a nearby stream flowing through a sparsely populated area. Because of difficulties related to source zone remediation, decision makers recently changed the short-term site management objective to mitigating discharge of polluted groundwater to the stream. To help formulating targeted remediation strategies pertaining to the new objective, we developed a groundwater numerical decision-support model. To facilitate reproducibility, the modelling workflow was scripted. The model was designed to quantify and reduce the uncertainty of surface water-groundwater (SW-GW) exchange fluxes for the studied period (2016–2020) through the use of history-matching. In addition to classical observations, thermal anomalies detected in fiber optic distributed temperature sensing (FO-DTS) measurements were used to inform the model of groundwater discharge. After assessing SW-GW exchange fluxes, we used measurements of surface water chemistry to provide a probabilistic estimation of mass influx and spatio-temporal distributions of contaminated groundwater discharge. Results show 1) SW-GW exchange fluxes are likely to be significantly larger than previously estimated, and 2) prior estimations of mass influx are located near the center of the posterior probability distribution. Based on this, we recommend decision makers to focus remediation action on specific segments of the stream.
... Chlorohydrocarbons are ubiquitous subsurface contaminants at many industrial sites worldwide (Aelion et al., 2010;Pankow and Cherry, 1996). After the release at the surface as dense non-aqueous phase liquid (DNAPL), chlorohydrocarbons rapidly migrate through the vadose zone into aquifers due to their physio-chemical properties (e. g. high density, low viscosity) making them exceptionally mobile, especially vertically down (Schwille, 1988). ...
... where f OC is the fraction of organic matter in the clay unit at the Laidlaw site (0.534%) determined by Parker (1996) and K OC is the soil organic carbon-water partitioning coefficient for PCE (380 mL/g (Pankow and Cherry, 1996). Moreover, the same values for the dry bulk density and the porosity determined by Parker (1996) were used for the linear as for the non-linear retardation factors (Eq. ...
This study aims to precisely determine the effective diffusion coefficients of chlorohydrocarbons in low permeable units under in-situ field conditions. To this end, two controlled release field experiments using TCE and PCE as dense non-aqueous phase liquids (DNAPLs) were conducted in two natural clayey deposits. Several months to years after the controlled DNAPL release, highly resolved concentration profiles were determined for the chlorohydrocarbons that had diffused into the clayey deposits. Effective diffusion coefficients for TCE and PCE were then determined by calibrating a 3D numerical and 1D analytical model, respectively, to the measured high-resolution concentration profiles. The simulations revealed that the effective diffusion coefficients vary by as much as a factor of four within the same low permeability unit being consistent with observed small-scale heterogeneities. The determined chlorohydrocarbon effective diffusion coefficients were further used to determine the equivalent thickness of DNAPL that would completely dissolve in an idealized, parallel-plate fracture by diffusion transport into clayey deposits for the time periods of the controlled release field experiments. The equivalent TCE and PCE DNAPL film thicknesses ranged between 36 and 581 μm, respectively, comparable and exceeding fracture apertures measured in naturally fractured clay rich deposits. Hence, films of DNAPL initially contained within fractures in clay-rich deposits can completely dissolve away within a few months to a few years due to diffusion. This stored contaminant mass poses a risk to adjacent aquifers if it is re-released due to diffusion out of the matrix after source depletion or remediation.
... How large are experimental uncertainties? DNAPLs can be present either as a single chemical compound or as complex, non-wetting phase mixture of several compounds with differing properties (e.g., PANKOW AND CHERRY, 1996). Chlorinated solvents such as trichloroethylene have been widely used for industrial processes such as dry-cleaning in the metal and mobile industry or the pharmaceutical (left), as well as the typical conceptual implementation in analytical or numerical models (right). ...
... production (e.g., LERNERAND BARRETT, 1996;PANKOW AND CHERRY, 1996;LOWE ET AL., 1999;GANDHI ET AL., 2002). The group of polycyclic aromatic hydrocarbons (PAHs) is associated with, for instance, coal tar that is used for street and roof sealing, creosote that is used for wood impregnation, raw petroleum oil leaking from pumping stations and pipelines, polychlorinated biphenyls that are used in electrical devices, and specific types of pesticides (e.g., MERCER ANDCOHEN, 1990;MONTGOMERY, 1991;LERNER ET AL., 2003). ...
Environmental pollution has become a global concern as consequence of industrializa-tion and urbanization. The ongoing subsurface contamination by dense non-aqueous phase liquids (DNAPLs) bears tremendous hazardous potential for humans and ecosys-tems including aquifer systems. Intended or accidental spill events have led to a vast number of registered sites affected by DNAPL type chemicals. Despite the existence of novel techniques for their exploration, characterization and remediation, economical constraints often limit efforts for risk prevention or reduction, so that information and data to characterize highly complex DNAPL contamination scenarios are often insuffi-cient and compensated by natural attenuation of groundwater-dissolved contaminant plumes. Especially, knowledge on the DNAPL source zone geometry (SZG) and source zone formation are critically required yet very scarce. Against the previously stated background, this cumulative doctoral dissertation critically examined the processes of DNAPL source zone formation at laboratory scale. A comprehensive literature review identified current limitations and open research questions in the latter research field, revealing evidence for the relevance of SZG for plume response at different scales. Giv-en only a limited number of published studies related to DNAPL source zone formation, two simplified experimental setups mimicking source zone formation in an initially fully water-saturated aquifer were developed and intensively tested. The performance of aqueous and non-wetting phase dyes was evaluated for DNAPL release into three non-consolidated porous media using reflective optical imaging in combination with a cus-tom-made image processing and analysis (IPA) framework. The latter suite allowed for the generation of physically plausible DNAPL saturation distributions with determinable level of uncertainty. Then, a limited number of DNAPL release experiments were per-formed under controlled ambient as well as with boundary and initial conditions to generate robust observation data, while further adopting the IPA framework. The latter data was introduced into a numerical multiphase flow model. While most system pa-rameters could be directly determined, the parameters defining the capillary pressure-saturation and relative permeability-saturation retention curves were inversely deline-ated through a classical Monte Carlo analysis. Overall, the successfully calibrated nu-merical setup mimicking the transient DNAPL source zone formation allowed to quanti-fy uncertainties related to the experiment, IPA framework and model setup configura-tion. In addition, a number of new research questions pointing towards future im-provements of laboratory-scale methodologies to understand DNAPL contamination were derived. Especially in light of numerous existing contaminated sites with unclear history and even more vague future, given by potential impacts through climate change and anthropogenic activity, an increasing need for sophisticated strategies to better un-derstand DNAPL contamination and to reduce hazard potential is expected.
Permanently accessible through QCOSA link: https://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa2-769788
... Chloroethenes are chlorinated solvents that have been used for many purposes, among them: metal cleaning and degreasing; cold and dry cleaning of textile products; degreasing of leather and wool; extraction of seed oils; removal of paints, lacquers, varnishes, waxes, and resins; manufacturing of adhesives, aerosols, phenol, aniline, insecticides, and dyes; intermediates in manufacturing chemical products; electronics; dielectric fluids; and heat transfer medium (Pankow and Cherry, 1996). They are dense non-aqueous phase liquids (DNAPLs) that are present in numerous pollution episodes associated with urban and industrial areas (Yu et al., 2015). ...
... Moreover, their variable hydrophobicity (Cwiertny and Scherer, 2010) conditions their sorption on soil materials. All of these factors have led them to become organic compounds that last in the environment for long periods of time (several decades or more; Pankow and Cherry, 1996). These compounds are carcinogenic (Yadav and Pandey, 2018), and their presence in soil and groundwater puts human health and ecosystems at risk (Cheng et al., 2016). ...
Chlorinated solvents occur as dense nonaqueous phase liquid (DNAPL) or as solutes when dissolved in water. They are present in many pollution sites in urban and industrial areas. They are toxic, carcinogenic, and highly recalcitrant in aquifers and aquitards. In the latter case, they migrate by molecular diffusion into the matrix. When aquitards are fractured, chlorinated solvents also penetrate as a free phase through the fractures. The main objective of this study was to analyze the biogeochemical processes occurring inside the matrix surrounding fractures and in the joint-points zones. The broader implications of this objective derive from the fact that, incomplete natural degradation of contaminants in aquitards generates accumulation of daughter products. This causes steep concentration gradients and back-diffusion fluxes between aquitards and high hydraulic conductivity layers. This offers opportunities to develop remediation strategies based, for example, on the coupling of biotic and reactive abiotic processes. The main results showed: 1) Degradation occurred especially in the matrix adjacent to the orthogonal network of fractures and textural heterogeneities, where texture contrasts favored microbial development because these zones constituted ecotones. 2) A dechlorinating bacterium not belonging to the Dehalococcoides genus, namely Propionibacterium acnes, survived under the high concentrations of dissolved perchloroethene (PCE) in contact with the PCE-DNAPL and was able to degrade it to trichloroethene (TCE). Dehalococcoides genus was able to conduct PCE reductive dechlorination at least up to cis-1,2-dichloroethene (cDCE), which shows again the potential of the medium to degrade chloroethenes in aquitards. 3) Degradation of PCE in the matrix resulted from the coupling of reactive abiotic and biotic processes—in the first case, promoted by Fe²⁺ sorbed to iron oxides, and in the latter case, related to dechlorinating microorganisms. The dechlorination resulting from these coupling processes is slow and limited by the need for an adequate supply of electron donors.
... Decades ago, chemicals-based industries engaged in expedient handling practices that were stunningly imprudent. 18,19 The result has been innumerable cases of groundwater contamination that have affected neighbors (e.g., by contaminating well water) who have zero benefit connection with the industries. For disconnected human third parties (as with consumers with product choice), the expectation is always zero risk. ...
... 21 By the late 1980s, many cleanup efforts were failing because of the persistent presence of large amounts of liquid solvent in the source zones. 19 By the early 1990s the lessons learned included (1) unless a source zone is highly localized (not common) and well understood (unlikely), remedial removal of even one-half of as little as 250 kg is enormously difficult; (2) the progressive removal of contaminant mass is subject to significantly diminishing returns: 22 getting the first half out leaves a second half that is much harder to get out. It is for this type of situation that MacDonald and Kavanaugh 23 predicted in 1994 that (1) significant restoration of most contaminated aquifers was an impossible goal; and (2) it would be advisible to "balance risk, technical feasibility, and costs for the best allocation of society's f inancial resources." ...
... Contamination of soil and groundwater by Dense Non-Aqueous Phase Liquids (DNAPL) is a major environmental issue. Because of the low aqueous solubility of many DNAPLs, DNAPL zones, particularly DNAPLs in pooled form or entrapped in low permeability regions, can persist in the subsurface environment for a long time (Mackay and Cherry, 1989;Pankow and Cherry, 1996). Remediation studies have shown that DNAPL removal using conventional pump and ex situ treatment technologies is a very slow process due to DNAPLs low solubility and mobility potential (Mackay and Cherry, 1989). ...
... A sketch of the experimental setup is shown in Fig. 1. The DNAPL mass was emplaced in the flow cell in pooled form which is commonly encountered in real contamination problems (Pankow and Cherry, 1996). The DNAPL considered is DCB, while ethanol was selected as the co-solvent for enhanced dissolution of the DNAPL. ...
Co-solvent flushing into contaminated soils is one of the most effective techniques for Dense Non-Aqueous Phase Liquid (DNAPL) remediation. In addition to the increase of DNAPL solubility, co-solvents (e.g. ethanol) can alter the viscosity and density of aqueous phase and diffusion coefficient of solute. Any changes in these parameters can change the flow behaviour and alter the upscaled DNAPL mass transfer coefficient which is a key parameter controlling soil and groundwater remediation at Darcy-scale. While numerous studies have investigated DNAPL remediation using co-solvents at the Darcy scale, pore-scale modelling of co-solvent enhanced DNAPL remediation has not been well investigated. In this work, a three-dimensional pore-network model was developed to simulate the 1,2-dichlorobenzene (DCB) remediation experiments using ethanol-water flushing solution. The model simulates the effect of changes in solubility, viscosity, density, and diffusion coefficient during co-solvent flushing of the DNAPL. The results of pore network modelling for ethanol-water flushing for the DCB remediation were also validated using the experimental data. In addition to pore-scale modelling, a continuum scale modelling (Darcy-scale) was used for the DCB remediation using ethanol-water flushing. The results of both pore network and continuum scale modelling demonstrated that the ethanol content and flushing velocity influence the interphase mass transfer and DNAPL dissolution process. The results indicated while the mass transfer coefficient decreased in the presence of ethanol, the process of NAPL remediation was improved due to the substantial increase of solubility in the presence of co-solvent. The large scale modelling showed that NAPL bank can be formed in the front of ethanol-water mixture flushing.
... They have widespread industrial applications, being used as solvents and in the manufacturing of chemical products. Generally, they have a higher density than water and exhibit relative persistence in biodegradation (Pankow and Cherry 1996). The main groups impacting the studied region are chlorinated ethenes, chlorinated ethanes, and chlorinated methanes (L'Apiccirella 2009; Barbosa 2015). ...
Investigating soil and water contamination is essential for assessing environmental risks and monitoring remediation processes. This study, located in São Paulo, Brazil, highlights the presence of chlorinated solvents, especially tetrachloroethylene, with the application of remediation measures such as chemical oxidation. Both contamination and remediation processes have led to changes in geophysical signatures, enabling the use of electrical resistivity, despite challenges in urban areas due to consolidated infrastructure. The objective is to integrate data from direct methods and surveys of electrical resistivity and induced polarization, obtained through direct current and resistive capacitive methods, to refine the conceptual model of the area, delineating the influence zone of the contaminant and remediation processes. The resistive capacitive method allows continuous data acquisition in large areas without the need for electrode insertion into the soil. Geoelectrical data, correlated with soil sample descriptions, allow analysis of subsurface characteristics and areas affected by contamination. Variations in resistivity identify differences between lithologies, while induced polarization highlights clayey areas. Chemical oxidation to remediate PCE contamination increases conductivity, allowing for delineation of the remediation's influence zone. Despite urban challenges, the electrical resistivity method helps fill data gaps and improve the conceptual model of the area, demonstrating a rapid and effective approach.
... Hu et al., 2016;Darlington et al., 2018). They can come from energy production (hydrocarbons), agriculture (pesticides), chemical and pharmaceutical industry (chlorinated solvents, polyethylene and other plastics, PFAS) as well as the production and use of military or firefighting equipment (PFAS, TNT) (Schwarzenbach et al., 2016;Pankow and Cherry, 1996). Widespread contamination can also come from poor management of landfills containing household and industrial waste (Bjerg et al., 1995). ...
... The rehabilitation of sites contaminated by dense non-aqueous phase liquids (DNAPLs), including chlorinated solvents, creosote and coal tar, remains a challenging environmental task (Pankow & Cherry 1996 ). DNAPL source zones (SZs) in the subsurface are highly complex and heterogeneous and provide a long-term source for contaminating groundwater and the environment (e.g. ...
Accurate characterization and monitoring strategies are essential for designing and implementing remedial programs for sites polluted with dense non-aqueous phase liquids (DNAPLs). Electrical resistivity tomography (ERT) is a widely used geophysical technique for mapping subsurface features and processes of interest and exhibits desirable characteristics for DNAPL sites due to its ability to gather large volumes of continuous subsurface information in a non-invasive, cost-effective, and time-efficient manner. However, ERT from the surface suffers from poor imaging quality with depth. Enhanced ERT imaging can be obtained via electrodes deployed on the surface and within horizontal boreholes, but so far it has only been investigated for two-dimensional (2D) imaging. This study evaluates the potential of three-dimensional (3D) surface-to-horizontal borehole (S2HB) ERT configurations for imaging 3D DNAPL source zones. Laboratory tank experiments were first conducted with a 3D S2HB ERT configuration, which consisted of a surface grid and a single borehole line of electrodes, being used to monitor DNAPL migration within porous media. Results demonstrate that 3D S2HB ERT with a single borehole provides improved sensitivity at depth, and therefore enhanced imaging compared to conventional 3D surface ERT. Further tank experiments were performed to assess the performance of single borehole S2HB ERT when (i) the distance between surface and borehole is increased, and (ii) additional horizontal boreholes are included. The S2HB ERT with a single borehole significantly outperforms surface ERT at larger depths and performs comparably to S2HB ERT with multiple boreholes. This study suggests that 3D S2HB ERT with a single borehole can provide the enhanced imaging ability needed to map DNAPLs, while also being relatively practical for implementation at field sites.
... They have widespread industrial applications, being used as solvents and in the manufacturing of chemical products. Generally, they have a higher density than water and exhibit relative persistence in biodegradation (Pankow and Cherry, 1996). The main groups impacting the studied region are Potassium permanganate is a strong oxidant that can be effectively used in the in-situ chemical oxidation process of anthropogenic chlorinated compounds (PCE). ...
Investigation of soil and groundwater contamination is essential for assessing environmental risks and monitoring remediation processes. Geophysical methods effectively map and characterize subsurface properties without requiring direct excavations. These methods provide data on geological structure, lithological changes, groundwater level, contaminant identification, and remediation process monitoring. Being non-invasive, they offer an advantage over drilling operations by avoiding the need for soil excavation. This reduces the risk of contaminant migration during investigation activities. The study area in São Paulo corresponds to a former industrial galvanization site where contamination by chlorinated solvents, especially tetrachloroethylene, occurred. Remediation measures such as pumping and treatment, multiphase extraction, soil/waste removal, and chemical oxidation were implemented in the area. The contaminant and remediation processes alter the geophysical signatures of the environment, enabling the use of the electrical resistivity method. However, applying this method can be challenging in urban areas due to pavement and urban interferences. The resistive-capacitive method was employed, allowing continuous data acquisition over large areas without the need to insert electrodes into the soil. Additionally, traditional electrical profiling and induced polarization were used to gather data at greater depths. The integration of geophysical methods with soil sample descriptions in liners provided an analysis of subsurface characteristics and affected areas. Although challenges exist in applying it to urban areas due to pavement and interferences, the electrical resistivity method can contribute to the Conceptual Site Model by filling data gaps between wells and delineating the contaminant's influence area and the chemical oxidation remediation process.
... Based on the distribution of contaminants in the source zone and plume, there are no indications that TCE DNAPL had migrated to the deeper saturated parts of the aquitard as it was observed at other sites, e.g., in Fjordbøge et al. (2017) or Puigserver et al. (2022). The measured concentrations at the test site were far below TCE solubility (Pankow and Cherry, 1996). The back-diffusion and leaching from the clayey till led to the evolution of a long and relatively narrow contaminant plume in the underlying sandy aquifer ( Fig. 1b-d), which migrated partly underneath the factory building and spread further in the sandy aquifer with the groundwater flow. ...
Point sources with contaminants, such as chlorinated solvents, per- and polyfluoroalkyl substances (PFAS), or pesticides, are often located in low-permeability aquitards, where they can act as long-term sources and threaten underlying groundwater resources. We demonstrate the use of a 3D numerical model integrating comprehensive hydrogeological and contamination data to determine the contaminant mass discharge (CMD) from an aquitard into the underlying aquifer. A mature point source with a dissolved chlorinated solvent in a clayey till is used as an example. The quantitative determination is facilitated by model calibration to high-resolution vertical concentration profiles obtained by direct-push sampling techniques in the aquifer downgradient of the contaminant source zone. The concentration profiles showed a plume sinking with distance from the source characteristic for such aquitard/aquifer settings. The sinking is caused by the interplay between infiltrating water and horizontal groundwater flow. The application of 3D solute transport modeling on high-resolution profiles allowed for determining the infiltration rate, the hydraulic conductivity in the aquitard, and, ultimately, the CMD. Different source zone conceptualizations demonstrate the potential effects of fractures and sorption in source zones in aquitards on CMD development. Fractures in the aquitard had a minor influence on the current CMD determined with the presented approach. Still, fractures with hydraulic apertures larger than 10 μm were crucial for the temporal development of the CMD and plume. A thorough characterization of the source zone conditions combined with high-resolution concentration profiles and detailed modeling is valuable for shedding light on the probable future development of groundwater contamination arising from sources in aquitard/aquifer settings and evaluating remedial actions.
... The increase in industrial activity over the past decades has led to a significant rise in anthropogenic contamination of groundwater, with Dense Non Aqueous Phase Liquids (DNAPLs) being a common form of these contaminants in aquifers. Due to its higher density than water, DNAPLs tend to migrate to the deeper levels of the groundwater system (Li et al., 2022;Luciano et al., 2010;Pankow and Cherry, 1996). These contaminants have a high persistence in the groundwater system, with residence times ranging from a few years to decades (Heron et al., 2016;Kavanaugh et al., 2003). ...
The use of numerical based multi-phase fluid flow simulation can significantly aid in the development of an effective remediation strategy for groundwater systems contaminated with Dense Non Aqueous Phase Liquid (DNAPL). Incorporating the lithological heterogeneities of the aquifer into the model domain is a crucial aspect in the development of robust numerical simulators. Previous research studies have attempted to incorporate lithological heterogeneities into the domain; however, most of these numerical simulators are based on Finite Volume Method (FVM) and Finite Difference Method (FDM) which have limited applicability in the field-scale aquifers. Finite Element Method (FEM) can be highly useful in developing the field-scale simulation of DNAPL infiltration due to its consistent accuracy on irregular study domain, and the availability of higher orders of basis functions. In this research work, FEM based model has been developed to simulate the DNAPL infiltration in a hypothetical field-scale aquifer. The model results demonstrate the effect of meso-scale heterogeneities, specifically clay lenses, on the migration and accumulation of Dense Non Aqueous Phase Liquid (DNAPL) within the aquifer. Furthermore, this research provides valuable insights for the development of an appropriate remediation strategy for a general contaminated aquifer.
... Most CAHs have octanol-water partitioning coefficients greater than 1 15 and are likely to sorb to aquifer materials. Contaminant DNAPL can act as a persistent source diffusing into 16 low permeability aquifer layers to be released slowly and at low concentrations creating large, dilute plumes 17 (Pankow, 1996). Chlorinated solvent remediation strategies commonly take advantage of the volatility of 18 the compounds utilizing air stripping or adsorption to treat groundwater or excavation of the DNAPL source 19 zone (Huang et al., 2014). ...
... When these organic contaminants infiltrate into the subsurface, they accumulate to form a separate phase and migrate downwards through the groundwater body until they pool above a non-permeable layer. In the zone of downward migration, residual saturations of the contaminant phase are left behind in the aquifer in the form of blobs and ganglia (Pankow and Cherry, 1996;Kueper, 2004). As oxidative reactions only take place in the aqueous phase, the injected oxidizing agents do not attack these remaining contaminant phases. ...
Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is an emerging innovative remediation technology for the treatment of dense non-aqueous phase liquids (DNAPLs). S-ISCO combines the solubilization of contaminants by means of surfactants with the chemical oxidation by an oxidizing agent, thus, potentially increasing the efficiency of the state-of-the-art ISCO technique. Scientific investigations are needed to enable the technology transfer for potential field applications based on the development of a remediation design under well-defined boundary conditions. For this purpose, experimental upscaling analyses were performed using the special infrastructure of the research facility for subsurface remediation (VEGAS). Batch tests showed that oxidation of the selected surfactant E-Mulse 3® (EM3) by activated persulfate (Na-PS) reduced the solubilization of the model contaminants 1,4-DCB, naphthalene, and PCE. As a consequence, the processes of contaminant solubilization and degradation were temporally and spatially separated in the developed remediation design. A proof of concept was provided by performing an S-ISCO medium-scale experiment (100 cm length, 70 cm height, 12.5 cm width), with 1,2-DCB as model DNAPL contaminant to be treated. A groundwater circulation well (GCW) was used to inject a 60 g/L Na-PS solution and to effectively mix the reagents. Sampling of the experiment's outflow and the soil material after treatment showed that neither rebound effects nor residual mass loadings on the soil material could be detected after termination of the S-ISCO treatment. To further evaluate the S-ISCO remediation design under field-like conditions, a large-scale S-ISCO experiment was conducted (6 m length, 3 m height, 1 m width), allowing for an extensive sampling campaign to monitor relevant processes. An efficient contaminant removal from the former source zone could be reached by surfactant solubilization, decreasing contaminant levels from initially over 2000 mg/L 1,2-DCB to final concentrations below 5 mg/L 1,2-DCB. The heterogeneously distributed contaminant degradation, implemented by a three-filter GCW, was attributed to density-induced migration processes that impeded an optimal reaction zone. A density-dependent numerical transport could qualitatively match the observations. By comparing different simulation scenarios, an adapted operation of the GCW was established that provides for a more efficient distribution of the density-influenced oxidant injection.
... (1) constituent concentration, (2) groundwater flux, and (3) the size of the source zone. This approach provides a more holistic representation of the risk posed to groundwater receptors compared with the use of only concentration-based regulatory criteria, along with other advantages (Pankow & Cherry, 1996;US EPA, 1998c, 2001. Because the health advisory levels that have been developed for some PFAS are very low (e.g., part-per-quadrillion levels for perfluorooctanoate [PFOA] and perfluorooctane sulfonate [PFOS] in US EPA, 2022b), and the maximum contaminant levels (MCLs) recently proposed by the US Environmental Protection Agency (US EPA) are in the low part-per-trillion range (US EPA, 2023), the use of mass discharge as a remediation metric may be even more important for PFAS than for more established contaminants ). ...
Soil‐to‐groundwater contaminant mass discharge (Md) is the authoritative metric defining source strength at sites impacted by per‐ and polyfluoroalkyl substances (PFAS) and is increasingly being reported. Accurate estimates of groundwater recharge at representative spatial scales, however, is critical to quantitatively estimating Md, which to date has received comparatively little attention relative to PFAS‐specific partitioning and retention processes within unsaturated zone source areas despite a plethora of available literature. The objective of this review is to summarize the concept of Md as it applies to PFAS‐impacted sites, present standardized terminology, and collate published literature on groundwater recharge for a practitioner‐level summary of practical methods. Critically, the primary aim is to reduce uncertainty in recharge (and, thus, Md) estimates commensurate to a given site management application (i.e., the data quality objective process). Therefore, we propose a tiered system of increasing cost, complexity, and certainty depending on specific project requirements and site conditions and recommend applicable recharge methods for each tier based on these factors. Ultimately, a framework is presented for the assessment of PFAS‐impacted source areas based on the concept of Md.
... DNAPLs, when spilled over a land surface, migrate downward dominantly through unsaturated regions and spread in longitudinal and transverse directions in the saturated zone below the water table, as shown in Figure 6. The spread and formation of DNAPL pools take place in the saturated zone if there exist any low-permeability regions (LPPMs), such as clay/silt lenses [39][40][41]. Thus, in this section, the potential physical, chemical, and biogeochemical governing factors controlling the evolution of dissolved-phase DNAPL plumes are discussed. ...
Dense nonaqueous phase liquid (DNAPL) in the subsurface environment beyond the permissible limit poses a threat to human health and a suite of ecological services. An accurate prediction of the concentration and mass fluxes of DNAPL at environmentally sensitive locations and their temporal variations can be obtained using robust and efficient fate and transport mathematical models. Thus, this study evaluated 412 articles published from 1990 to 2022 utilizing the Scopus® database to provide a quantitative overview of the present trends and future perspectives of the DNAPL transport research field, especially fate and transport models via bibliometric analysis. The major findings of the published literature based on the scale of the study and type of modeling framework, relationships of governing parameters with a scale of study, and recent developments in the mathematical models were discussed. The country-citation analysis revealed the USA and Canada as leading countries in DNAPL fate and transport research field. The findings of this study uncovered a need for studies considering low-permeability and stagnant regions, as well as the variable nature of the flow, transport, and reaction parameters to understand the complex plume evolution dynamics of DNAPLs under field-scale conditions. The nonlinear interactions between various flow and transport phenomena should be quantified during a model’s development by applying spatial- and time-varying global sensitivity analyses. The outcomes of the bibliometric survey, visual analysis, and concise review presented in this study can provide a wide range of references, emerging topics, and prospects to emphasize less focused on topics of DNAPL transport research.
... 18 In this respect, conducting polymers have been studied extensively, and the difficulties connected with these materials may be overcome by the advancement of dopant acid, doping amount, or blending with other polymers/metals, etc. 19 The detection of dangerous vapours like chloroform has long been difficult since they are always released into the environment by a wide range of human activities, unlike the aforementioned analytes. Because of its high solubility in water at room temperature (∼25°C), its potential for causing groundwater contamination, and the severe negative impact it has on human health, 20 it is one of the most pressing environmental problems. Thus, precise monitoring is crucial, but difficult, since most sensors are very sensitive to several environmental conditions like temperature, humidity, etc. 21,22 Nitric oxide (NO), carbon monoxide (CO), and other toxic gases are very harmful to live organisms, making their detection crucial. ...
Due to global industrialization, monitoring the number of gases and volatile compounds in the environment greatly affects sustainable human development. Since the 1970s, gas sensors have been used to find harmful gases and gas leaks, as well as to measure humidity and the composition of the atmosphere. Designing small, portable gas/vapor sensors with fast response, reversibility, selectivity, and sensitivity has been difficult. In a similar way, advances in nanotechnology have led scientists to make nanosensors. The development of sensors from traditional semiconductors, solid electrolytes, insulators, metals, etc. However, advances in sensor technology based on conducting polymers have opened up a new way of sensing by making it possible to find chemical/water vapors and industrial waste gases even in complex environments. On the other hand, metal-based sensors were found to be good at detecting industrial waste gases. This review summarizes the work on conducting polymers and metal-based sensors for detecting ammonia, alcohol, chloroform, humidity, industrial waste gases, and other things. The shortcomings and future improvements in the sensing performance of conducting polymer sensors are discussed additionally in this literature review.
... 유류 유출로 인한 토양 오염은 전 세계적으로 토양을 오염시키는 주요 오염원으로 알려져 있다 (Nadim et al., 2000). 유류의 대부분은 물에 잘 용해되지 않는 소수성 물질로 토양에 유출되면 강한 흡착 및 공극 내에 남아 오랜 기 간 잔류하면서 주변 환경을 오염시킨다 (Pankow and Cherry, 1996). 유류 중 토양으로 유입된 석유계총탄화수소 (total petroleum hydrocarbons, TPH)는 토양 내 오랜 기간 잔류하는 오염물질로 작물의 생육을 저해하고 인체의 영 향을 미치는 물질로 총 탄소수가 8 -20에 해당되는 화학물질이며, 현재 우리나라의 경우 토양환경보전법에 의해 TPH는 토양오염우려기준 2,000 mg kg -1 , 토양오염대책기준 5,000 mg kg -1 로 규정하여 관리되고 있다 (Jung, 2003;Nwankwegu and Onwosi, 2017). ...
... During the past three centuries, municipal and industrial waste disposal as well as mining and industrial activities led to the widespread contamination of soils and, surface-and groundwater systems worldwide (Agostini et al., 2012;De Sousa, 2001;Pankow and Cherry, 1996;Pizzol et al., 2011;Swartjes et al., 2012;Wang et al., 2012;Wanner et al., 2015Wanner et al., , 2018Wiedemeier et al., 1999;Zabeo et al., 2011). Nowadays, the most frequently detected pollutants at contaminated sites are metals, mineral oil, chlorohydrocarbons, volatile aromatic hydrocarbons (BTEX), and polyaromatic hydrocarbons (PAH) (Panagos et al., 2013). ...
To classify contaminated sites into different risk classes, many different methods exist in Europe and worldwide. However, no systematic comparison of European risk classification methods has been carried out so far to carve out the advantages and disadvantages of the methods and to homogenize them. To address this research gap, this study aims at comparing the Swedish Method for Inventories of Contaminated Sites (MIFO) with the German Individual Assessment of Contaminated Sites Method (EB) from the Hessian Agency for Nature Conservation, Environment and Geology (HLNUG) regarding the risk class categorization of 51 contaminated sites. The results revealed that with the MIFO 39% fewer contaminated sites are assigned to risk classes 1 and 2 and thus, subject to remediation compared to the EB. Moreover, in comparison to the EB, the MIFO showed a lower comparability, traceability, and a larger room for interpretation, which could be related to the lack of a quantitative approach such as a point or ranking system in the MIFO. Hence, we recommend providing the MIFO and other methods that lack a quantitative approach with a point and/or ranking system, similar to the EB, to increase their objectivity for the risk class categorization of contaminated sites.
... NAPLs lighter than water (e.g. many petroleum chemicals such as benzene, toluene, xylene, etc.) are called light nonaqueous phase liquids (LNAPLs), and those heavier than water (e.g., chlorinated solvents, coal tar) are named dense non-aqueous phase liquids (DNAPLs) (Huntley and Beckett, 2002;Mercer and Cohen, 1990;Pankow and Cherry, 1996). ...
The remediation of DNAPL-contaminated soil with lower-density fluids is ineffective due to the over-riding of displacing fluid. The densification of biopolymers is experimentally studied to develop a solution with the same density as a pollutant. Polymer solutions and contaminants are characterized through rheometer. A 1D column filled with monodisperse glass beads was used to measure their apparent viscosity in porous media. The displacement of pollutants by biopolymers (such as xanthan gum, guar gum, and carboxymethyl cellulose) and densified solutions based on barite are investigated in the 1D porous column. In addition, the polymer solution flow is studied using an upscaling method based on the shear viscosity measured with rheometer. The upscaling results are compared with the 1D column experimental outcomes. We found that carboxymethyl cellulose is the best for densifying polymer and showed the highest remediation yield for DNAPL remediation. The polymers' rheology was represented well through the Carreau rheological model. The discrepancy of apparent viscosity in porous media from polymers' shear viscosity measured with rheometer is explained by the adsorption of polymers on pore surfaces and deposition of barite particles in a porous medium, which led to a decrease in permeability. The upscaling results are in good agreement with experimental outcomes at low-pressure gradients. The impact of porous media geometry on polymer flow in porous media is described.
... Pollution of soil due to dense non-aqueous phase liquid (DNAPL) spilling has become a crucial issue of concern during the last decade, causing numerous geo-environmental (e.g., mitigation of DNAPLs on aquifers) problems (Habiyakare et al., 2022). In polluted sites, DNAPLs sink below the water table and cause dissolved plumes in the subsurface (Pankow and Cherry, 1996;Power et al., 2014). After many years of research, soil contamination due to DNAPLs is still one of the main challenges for the environmental and geophysical communities (Kavanaugh, Suresh and Rao, 2003). ...
In this decade, electro‐geophysical methods are widely used in different environmental subjects. Study on soil remediation polluted by DNAPLs has become a certain need for all countries. Geoelectrical methods show their potential to facilitate evaluating decontamination processes. Our challenge in this study was to understand how coupled temperature and saturation changes affect electro‐geophysical parameters in a contaminated 2D sample. The primary objective was to evaluate the efficiency and potential of spectral induced polarization (SIP) for monitoring the recovery of dense non‐aqueous phase liquids in contaminated porous media. A set of 2D tank experiments investigated the impacts of temperature and saturation changes on the electrical complex resistivity of a saturated porous medium under non‐isothermal conditions. The measurements were made with a coal‐tar and water fluid pair in a porous medium that has been simulated by 1 mm glass beads. We circulated hot water around the tank and used an immersion heater to heat the porous medium in the tank at different stages. The SIP technique (also called complex resistivity) was used to measure the complex electrical resistivity of a medium in the frequency domain. The experimental results for a simple drainage case were validated using numerical modeling. The complex electrical resistivity was used to obtain the saturation field before and after imbibition. For this purpose, the generalized Archie's law obtained for the same fluid pair with 1D cells (with a vertical flow) was used. Our results from electrical resistivity measurements for saturation fields are in accordance with 2D tank images and can illustrate the saturation change with pointwise resistivity measurements. The results show that saturation change has the main role in electrical resistivity variation compared to temperature (5 to 7%). We also studied the effects of temperature change on the Cole‐Cole parameters and the results confirm our previous findings with the same variation trend in these parameters. The results from varying electrical complex resistivity from the 2D tank (with vertical and horizontal flow) in the laboratory conditions will help us to understand the coupled temperature and saturation effects on complex resistivity in a real polluted site case. Proper application of spectral induced polarization (SIP) in samples polluted by dense non‐aqueous phase liquids (DNAPL) Temperature and saturation separately affect electrical complex resistivity Temperature has a considerable effect on Cole‐Cole parameters in a 2D tank Saturation changes have a remarkable impact on phase shift 2D tank results on complex resistivity confirm 1D cell findings This article is protected by copyright. All rights reserved
... Within the saturated zone, it can be exhausted as residual saturation, or it can migrate laterally depending on the permeability of the soil. In any case, DNAPLs occupy an area in the saturated zone either in quasi-or steady-state and become a long-term source of the contaminated plume (Pankow and Cherry, 1996). ...
Many studies have investigated the migration and entrapment processes of source zones from dense non-aqueous phase liquid (DNAPL) contamination under different conditions. However, the characterization of occupying area by source zone (or source shape) in water-saturated aquifers is still rudimentarily considered. In this study, we demonstrated this issue (1) by providing a brief review of existing approaches for source shape consideration, (2) by proposing an approach with simple shape parameters based on the non-uniformity of source widths, and (3) by providing exemplary applications of our proposed approach on shapes already published in previous research works. Our literature review suggested that the source zone in mathematical approaches is generally characterized as simple geometrical shapes (arbitrary lines or rectangles) or system-defined parameters that contrast to complex and discontinuous shapes observed in the real world. But the characterization of such complex shapes is still not possible with acceptable efforts. Therefore, we proposed an approach to parameterize the source shape by considering the variation of width and midpoints over the depth of the entire source zone and formulate four parameters based on population statistics (mean, standard deviation). To illustrate the suitability of our approach, we applied it to the results of lab experiments, and by analyzing these complex shapes, we highlighted the potential for improving the characterization techniques of non-uniformity of the source zones.
... M ultiphase transport theory clearly allows for nonaqueous phase liquid movement over large distances through porous media as dictated by physical and chemical driving and facilitating parameters such as non-aqueous phase fluid and porous media properties [1][2][3][4] . However, available literature generally presume that chlorinated solvent dense nonaqueous phase liquid (DNAPL) transport and deposition is limited to a maximum of tens of meters from the release area in most contaminated site scenarios [5][6][7][8][9][10][11] . ...
Here we confirm migration of chlorinated solvents tetrachloroethene and trichloroethene, and co-disposed elemental mercury as dense non-aqueous phase liquid in an aquifer at a scale larger than previously documented in the literature, over 650 m from original surface discharge. This finding enhances the conceptual model explaining extensive contaminated plume persistence by adding structurally controlled dense non-aqueous phase liquid to known mechanisms such as source dissolution and matrix back-diffusion. Following injections of oxidants at a depth greater than 50 m, which effectively destroyed dissolved chlorinated contaminants during a groundwater remediation pilot test in South Carolina, we measured excess chloride higher than attributable to pre-test dissolved concentrations of chlorinated contaminants, and oxidative releases of mercury, which is an opportunistic tracer of non-aqueous phase solvent transport when in its elemental form. The results suggest potentially targeted destruction strategies in disconnected non-aqueous phase liquid accumulation areas may reduce remediation timeframe and support cleanup of sites previously considered technically impracticable.
... In environmental terminology, the immiscible liquid phase in groundwater is known as non-aqueous phase liquid (NAPL), the combination of isostatic forces and capillary pressure effects results in these being distributed across the water-table, or confined below the water-table but occurring near the top of the confined coarser grained unit. When an immiscible liquid phase of the TCE compound comes into contact with the aquifer, the product forms a non-aqueous phase liquid denser than water, known as dense non-aqueous phase liquid (DNAPL), because its specific mass (1.46 kg dm -3 ) is greater than that of water 9 . The risk associated with DNAPL contamination is specific to the types of chemical compounds and is generally persistent in the environment 10 . ...
Contamination of the unsaturated zone, and hence, of groundwater by non-aqueous phase liquids has become a problem that arouses great concern due to the environmental damage it causes. Several efficient and economically beneficial techniques for the in situ treatment of contaminated soils have been applied quite frequently, including the so called soil flushing processes. In this study, microemulsion systems were prepared using limonene, in the search for a formulation that would remove trichloroethene in soil. Limonene, a monocyclic monoterpene, is one of the main constituents of various essential oils of citrus fruits, such as oranges, tangerines and lemons. The results indicated that using a washing fluid containing 15 % DL-limonene microemulsion enabled the removal of 98.85 % of trichloroethene present in the soil after 30 minutes of residence time in the system. Hence, it can be concluded that the use of this microemulsion system is an interesting strategy for the remediation of soils contaminated with trichloroethene.
... Underground contamination by chlorinated ethenes ("CEs" hereafter) is a well-known global environmental issue. Indeed these contaminants are widespread in most aquifers underlying industrial and urbanized areas, persistent in the underground due to their mobility and poor degradability (Olaniran et al., 2004;Pankow and Cherry, 1996), and toxic/carcinogenic to the human health (e.g., Chen and Wu, 2017). ...
Chlorinated ethene (CE) contaminants are widespread in groundwater, and the occurrence of vinyl chloride (VC), among others, is a well-known issue due to its mobility, persistence, and carcinogenicity. Human exposure to VC may occur through inhalation after soil vapor intrusion into buildings at sites with shallow underground contamination. Soil vapor intrusion risk is traditionally assessed through indoor air and sub-slab sampling (direct evidence) or soil gas and groundwater surveys (indirect evidence). Phytoscreening (sampling and analysis of tree trunk matrices) was proven as a cost-effective alternative technique to indirectly detect shallow underground contamination by higher chlorinated ethenes and subsequent vapor intrusion risk. However, the technique has appeared barely capable to screen for the lower chlorinated VC, likely due to its fugacity and aerobic bio-degradability, with only one literature record to date showing successful detection in trees. We applied phytoscreening at two sites with severe CE contamination nearby residential buildings caused by illegal dumping of chlorinated pitches from petrochemical productions. The two sites show variable amounts of VC in the shallow groundwater (1e2 to 1e4 μg/L), posing potential sanitary risk issues. Former soil gas surveys did not detect VC in the vadose zone. At both sites, we sampled trunk micro-cores and trunk gas from poplar trees close to contaminated piezometers in different seasons. VC was detected in several instances, disproving the shared literature assumption of the inefficacy of phytoscreening towards this compound. Factors influencing the detectability of VC and other CEs in trees were analyzed through linear regressions. Two different conceptual models were proposed to explain the effective uptake of VC by trees at the two sites, i.e., direct uptake of contaminated groundwater at the first site and uptake of VC from an anoxic vadose zone at the second site. In planta reductive dechlorination of CEs is not expected based on current literature knowledge. Thus, the detection of VC in trunks would indicate its occurrence in the shallow underground, suggesting higher screening effectiveness of phytoscreening compared to soil gas; this has implications for indirect vapor intrusion risk assessment.
... Chlorohydrocarbons are widespread environmental contaminants, especially in industrialised countries (Pankow and Cherry, 1996). After their release at the surface as dense nonaqueous phase liquid (DNAPL), chlorohydrocarbons readily migrate vertically into the subsurface due to their higher density, lower viscosity and lower surface tension compared to water (Johnson et al., 1989;Kueper et al., 1993;Parker et al., 2004;Schwille, 1988). ...
Compound-specific isotope analysis (CSIA) has been increasingly used to understand and quantify the (bio)degradation processes affecting chlorohydrocarbons in aquifer-aquitard systems. In this study, we aimed at investigating through reactive transport simulations if dual element (C, Cl) CSIA in aquifer samples can provide information about the occurring (bio)degradation pathways in the underlying aquitard. To that end, we modeled the continous dissolution of a 1,1,2,2-tetrachloroethane (TeCA) dense nonaqueous phase liquid (DNAPL) source in an aquifer as well as the resulting TeCA groundwater plume formation and diffusion into the underlying aquitard. The (bio)degradation of TeCA in the aquifer-aquitard system was simulated in four scenarios: TeCA biodegradation via dehydrohalogenation to TCE and TeCA dichloroelimination to cDCE in the aquifer as well as in the aquitard. The simulations revealed that dual element (C, Cl) CSIA in the aquifer allows the disentanglement of whether TeCA degradation occurs in the aquifer or the aquitard and which (bio)degradation pathways occur in the aquitard. This demonstrates that chlorohydrocarbon (bio)degradation pathways in aquitards can be identified based on CSIA aquifer measurements only, which is an advantage as aquifers are easier to monitor than aquitard.
... In other cases, it is not the solid phase of porous media that changes the density, but the varying presence of fluids. Examples include (1) the variably-saturated flow of water through porous media, e.g., in the vadose zone in the area of soil science (e.g., van Genuchten, 1980) or (2) the multiphase flow of non-aqueous phase liquids (NAPLs) through otherwise water-saturated porous media in the area of contaminant hydrology (e.g., Pankow & Cherry, 1996). ...
Several environmental phenomena require monitoring time-dependent densities in porous media, e.g., clogging of river sediments, mineral dissolution/precipitation, or variably-saturated multiphase flow. Gamma-ray attenuation (GRA) can monitor time-dependent densities without being destructive or invasive under laboratory conditions. GRA sends gamma rays through a material, where they are attenuated by photoelectric absorption and then recorded by a photon detector. The attenuated intensity of the emerging beam relates to the density of the traversed material via Beer–Lambert’s law. An important parameter for designing time-variable GRA is the exposure time, the time the detector takes to gather and count photons before converting the recorded intensity to a density. Large exposure times capture the time evolution poorly (temporal raster error, inaccurate temporal discretization), while small exposure times yield imprecise intensity values (noise-related error, i.e. small signal-to-noise ratio). Together, these two make up the total error of observing time-dependent densities by GRA. Our goal is to provide an optimization framework for time-dependent GRA experiments with respect to exposure time and other key parameters, thus facilitating neater experimental data for improved process understanding. Experimentalists set, or iterate over, several experimental input parameters (e.g., Beer–Lambert parameters) and expectations on the yet unknown dynamics (e.g., mean and amplitude of density and characteristic time of density changes). We model the yet unknown dynamics as a random Gaussian Process to derive expressions for expected errors prior to the experiment as a function of key experimental parameters. Based on this, we provide an optimization framework that allows finding the optimal (minimal-total-error) setup and demonstrate its application on synthetic experiments.
... 35 It is considered as one of the major concerns since it possesses high solubility in water at room temperature (~25 o C), can easily result in groundwater pollution also leads to serious deteriorating effects to human health. 36 Therefore, accurate monitoring is essential, but is highly challenging since most of the sensors are very susceptible to many environmental factors such as temperature, humidity, etc. 37 The detection of various noxious gases such as nitric oxide (NO), carbon monoxide (CO), are of vital importance due to their enormous physiological impact. Perovskite materials were found to be potential candidates for sensing gases however, the structural and morphological intricacies dictate their sensing mechanism. ...
Monitoring the concentration of gases and volatile compounds in the environment has significant impact on sustainable human development due to global industrialization. Gas sensors are being employed since 1970's for detecting noxious gases, gas leakages, and also for observing humidity and atmospheric composition. The approach of designing miniature and portable gas/vapour sensors exhibiting rapid response and reversibility together with selectivity and sensitivity has been highly demanding. Similarly, development in the area of nanotechnology has encouraged the scientists to fabricate nanosensors. Sensor devices have been made from classical semiconductors, solid electrolytes, insulators, metals etc. However, the development of conducting polymer-based sensors has unfolded a new dimension in sensing by enabling the wide scope towards the detection of chemical/water vapours and toxic gases even in complex environment. Whereas, the metal oxide-based sensors were observed to be efficient towards the detection of toxic gases. The present review provides a concise account of our work on conducting polymers and metal-based sensors for the detection of ammonia, alcohol, chloroform, humidity, toxic gases etc. Additionally, the paper also demonstrates the challenges and future prospects of conducting polymer sensors to pave their way for enhancing their sensing efficacy.
... Chlorinated solvents PCE and TCE found widespread use over the past century in degreasing and dry-cleaning operations (Doherty, 2000). Chlorinated solvents are volatile, immiscible in water, denser than water, and exhibit varying solubilities (Pankow and Cherry, 1996;National Library of Medicine, 2021). As such, when chlorinated solvents are released into the environment through accidental spills and leaks, they can readily migrate through subsurface media and contaminate groundwater. ...
Conventional testing methods provide sufficient information to evaluate human or ecological risk. However, contaminant concentrations patterns alone provide only limited resolution of important liability issues, such as when and where did contaminant releases originate. Over the past few decades, scientists explored the isotope applications to better identify, delineate, and manage contaminants in the environment. Advanced chemical fingerprinting and isotope technologies revealed important linkages between isotope ratios and contaminant origins (e.g., chemical feedstock and manufacturing process). Studies of environmental weathering distinguished abiotic and biotic changes in the chemical composition and isotope patterns. The combined application of chemical and isotopic fingerprints offers powerful complementary lines of evidence for delineating contaminants, assessing risk, and identifying historical sources. This manuscript provides an integrated forensic approach that systematically links conventional environmental investigation data with specialized chemical fingerprinting and carbon/chlorine isotope methods for identifying the sources of groundwater impacts especially when multiple potential point and non-point sources exist. This paper focusses on chlorinated solvents. Specifically, it features the synoptic use of chemical concentration patterns and compound-specific isotope analysis (CSIA) as effective tools for confirming organic contaminant sources, characterizing environmental weathering, and answering a growing list of site-specific questions. Unlike conventional isotope methods, which can be both time-consuming and expensive, this paper presents an optimized analytical method for chlorine CSIA using gas chromatography-quadrupole mass spectrometry (GC-qMS). Chlorine isotopic composition for multiple analytes (e.g., tetrachloroethylene [PCE], trichloroethylene [TCE], dichloroethylene [DCE], and vinyl chloride [VC]) can be determined in one acquisition thus reducing analysis time and cost. Precise CSIA isotope values were achieved for chloroethylene concentrations between approximately 5 micrograms per liter (ug/l) and 100 ug/l for carbon and between approximately 30 ug/l to 1,000 ug/l for chlorine. The gradual improvement in CSIA methods better addresses the wide concentration range encountered in typical samples collected from groundwater aquifers with significant chlorinated solvent impacts. A case study is presented featuring a tiered forensic investigation using spatial chemistry and isotope patterns to evaluate commingled plumes of PCE and TCE.
... Dense nonaqueous phase liquids (DNAPLs) are widespread contaminants that threaten environmental and human health due to their extensive use, improper disposal, and resistance to remediation (Council, 2005;Pankow and Cherry, 1996;Rao et al., 1997). Although part of free-phase DNAPL can be removed by pump-and-treat, the DNAPL adhering to the surface of the media and trapped in the pore throat or corner is difficult to remove completely. ...
Colloidal biliquid aphron (CBLA) is a strong density modifier for dense nonaqueous phase liquids (DNAPLs). However, the underlying mechanisms responsible for density modification and displacement is not yet clear. Here, a series of batch column and sandbox experiments were conducted to achieve substantial removal and irreversible density reduction of tetrachloroethylene (PCE). The mass of PCE retained in the column and sandbox was less than 1% under suitable injection conditions, and the density of PCE in the effluent was less than that of water (fluctuated in the range of 0.74~0.96 g/cm³). The displacement process was controlled by the high viscosity ratio of CBLA to PCE (52.3). The emulsified and dissolved phase of PCE formed after reaction with CBLA, and the light nonaqueous phase liquid (LNAPL) phase formed after injecting demulsifier solution. The phase analysis played a significant role in monitoring the changes in concentration and density of PCE. The density-modification displacement technique using CBLA reduced the mass of residual PCE by a factor of 165 compared to surfactant flushing, and there was no risk of downward migration of PCE. This study contributes to a better remediation of entrapped DNAPL in contaminated aquifer.
... The distribution range of DNAPLs in the rock strata is estimated based on sample drilling and the permeability theory. Pankow and Cherry [7] proposed that, when DNAPLs are released from the ground, they will move both vertically and horizontally underground. Some DNAPLs will remain at the bottom of the overburden, whereas the rest will move to a significant depth within the fractured rock mass. ...
To investigate the seepage characteristics of dense nonaqueous phase liquids (DNAPLs) in rock fractures, two types of NAPLs (paint and creosote) were used in triaxial permeability tests conducted on single-fracture samples. The hydraulic conductivity of rock fractures with different apertures, confining pressures, and fluid properties was measured, and the influence of various physical factors on transmissivity was explored. The results demonstrated the following: (1) Fracture aperture and fluid viscosity are the main factors influencing transmissivity; (2) The widely used cubic law fails to effectively predict the transmissivity of high-viscosity liquids in a fracture, and the influence of liquid viscosity is considerably higher than that predicted by the cubic law; and (3) This study proposed a transmissivity prediction model of DNAPLs in a rock fracture based on multivariate regression analysis. The proposed model provides more accurate prediction results than those predicted by the cubic law, and is applicable to fracture apertures ranging from 5 × 10−4 to 2.5 × 10−3 m as well as to every kind of fluid used in this study.
... The presence of DNAPL was visually confirmed at GW-1S, GW-1M, and GW-1D during the groundwater sampling event. In addition, DNAPL were likely to be present at the majority of monitoring wells, with the exceptions of GW-3M and GW-4D, based on the rule of thumb that NAPL is likely to exist if the concentration of NAPL-related chemicals in groundwater is ≥1% of its effective solubility (Feenstra and Guiguer, 1996;Pankow and Cherry, 1996). The total concentration distribution of cVOCs in aquifer solids at various depths are shown in Fig. S2. ...
Fluorochemical industrial park (FIP) represents an important source of per- and polyfluoroalkyl substances (PFASs) and chlorinated volatile organic compounds (cVOCs). Exploring the co-occurrence and correlations of PFASs and cVOCs is a key step towards the understanding their distributions in the field. In this study, perfluorooctanoic acid (PFOA) was the dominant compound in groundwater and aquifer solids, and elevated concentrations of short-chain perfluoroalkyl carboxylic acids (PFCAs) and hexafluoropropylene oxide oligomers were also detected in the field, suggesting their wide applications as substitutes for PFOA. Correlation analyses between PFASs and cVOCs suggested that cVOCs had a significant influence on the distribution and composition of PFASs in the field. In addition, the presence of cVOCs in the form of dense non-aqueous-phase organic liquids (DNAPL) affected the distribution and migration of PFASs at various depths, as evidenced by the relatively high PFASs concentrations (204 μg/L) and PFOA abundance (85.4%) in the deep aquifer, likely due to DNAPL-water interfaces sorption or partition into bulk DNAPL. The log Kd values, determined in the laboratory, were found to increase in the presence of DNAPL, especially for PFOA, with more than one time higher than those of perfluorobutanoic acid (PFBA) and hexafluoropropylene oxide dimer acid (HFPO-DA). This conclusion further demonstrated that PFOA had a higher potential to participate into DNAPL, which can migrate with DNAPL to the deep aquifer, supporting the higher abundance of PFOA in the deep aquifer mentioned above. However, the log Kd-field values of PFBA and HFPO-DA in the field were higher than that of PFOA, and no significant correlations (p > 0.05) were found between log Kd-field values and the chain-length of PFCAs at various depths, suggesting that the phenomena observed in the field are a result of composite influencing factors.
... For example, one of the motivations of this work has been the "chloroform problem" in which it has been suggested that there are competing reaction pathways for the degradation of CCl 4 that can produce unfavorable and favorable metabolites (180)(181)(182)(183)(184)(185)(186)(187)(188)(189). Unfortunately, many groundwater remediation strategies follow an unfavorable pathway in which they produce chloroform (CHCl 3 ) as the major product and methylene chloride (CH 2 Cl 2 ) as a minor product. ...
Over the last few decades, significant progress has been made in the development and use of electronic structure and other molecular simulation methods. As these methods become more mature and are able to perform larger and more complex chemical simulations, the need for improvement in scientific visualization, molecular builders, simplified input to simulation methods, and the development of new approaches and languages to describe simulations, along with workflows to carry them out, becomes more apparent. In this chapter, we describe our recent efforts in developing a prototype open-source computational tool called Arrows that combines NWChem, SQL and NoSQL databases, email, web APIs, and web applications in a way that makes molecular and materials modeling accessible to all scientists and engineers. At the same time, because of its simplified input, it provides a framework for expert users to carry out large numbers of calculations and run complex workflows.
... Also, (Colombano et al., 2021) only worked in isothermal conditions. Their recovery by pumping can therefore change the observed results (Pankow and Cherry, 1996;Li and Schwartz, 2004;Childs et al., 2006). Moreover, thermal techniques for soil remediation have also already been studied on this scale. ...
Thermal enhancement is known to be an efficient way to decrease the residual saturation of some common dense non-aqueous phase liquids (DNAPLs) after pumping. However, the effect of transient heat transfer during the recovery of a high-viscosity contaminant, such as coal tar, in highly permeable porous media is still unknown. A 2D tank experimental setup allowing monitoring of temperature and saturation fields during DNAPL pumping has been developed. Experiments were run under isothermal and non-isothermal conditions, at low and high flow rates. We investigated the presence of viscous fingering and how that influences the shape of the cone of depression, as well as the residual saturation. The saturation fields show that less viscous fingering occurs in pre-heated cases and that heating increases the recovery efficiency. Increasing the temperature increases the critical velocity and the viscosity ratio and helps to stabilize the interface between the non-wetting and wetting phase. Observations were first made on an oil and ethanol fluid pair because its properties were known, before extending the experiments to a coal tar and water fluid pair. Residual oil saturation after pumping was decreased by 6–16% in all pre-heated conditions. Pumping at low flow rate in these conditions leaves the smallest oil residual saturation (20%) after pumping. A low flow rate increases the recovery efficiency by reducing viscous fingering and by spreading the generated heat to a larger part of the tank. Finally, results on coal tar pumping show that the high thermal conductivity of water helps in keeping the temperature high during pumping. The residual coal tar saturation was reduced from 40% at 20 °C to 28% when pre-heating the tank. Operating at a low flow rate and with a uniform temperature is the key to recovering the highest amount of a viscous DNAPL such as coal tar from the soil and satisfying cleanup goals when using thermally enhanced pumping.
... CSIA involves the measurement of the relative proportions of a given compound's different isotopolocules (i.e., molecules differing only in isotopic composition), which can be influenced by various chemical and physical processes. Chloroethenes such as trichloroethene (TCE) and cis-dichloroethene (cDCE) are the most common CHCs present as groundwater contaminants (Pankow and Cherry, 1996;Wiedemeier et al., 1999). Much of the development and application of CSIA for CHCs in the saturated zone has assumed that only reactive processes (abiotic and biotic) are associated with an isotope effect (e.g. ...
Isotopic fractionation of groundwater contaminants can occur due to degradation, diffusion and sorption. Of these, only degradation has been extensively explored, yet diffusive isotopic fractionation (DIF) and sorptive isotopic fractionation (SIF) can have significant effects on the isotopic enrichment of groundwater contaminants. Understanding how to mathematically describe and model these processes is vital to the correct interpretation of compound-specific isotope analysis (CSIA) data in the field. Here, models for these physical fractionation processes are developed and described, including the definition of a sorption enrichment factor. These models are then implemented numerically using inverse and finite-element methods to investigate two scenarios, diffusion-sorption and diffusion-sorption-advection, that have been measured in the laboratory. Concentration, δ37Cl, and δ2H data from cis-dichloroethene (cDCE) and trichloroethene (TCE) are used as inputs to the models. Unknown transport parameters including diffusive fractionation exponents are determined from an inverse modelling approach. DIF is shown to have a stronger influence on chlorine isotopologues than on hydrogen isotopologues. For both cDCE and TCE, the sorption enrichment factor of chlorine is found to be negative while that of hydrogen is positive. The presented approach and results provide novel tools and insight into DIF and SIF and underline that these processes should be taken into account when using CSIA to assess contaminant fate.
... Chlorinated solvents like tetrachloroethylene and tetrachloroethylene are common examples of DNAPL, while petroleum compounds like benzene, toluene, and xylene (BTEX) are common examples of LNAPL [5][6][7]. LNAPLs migrate downward through unsaturated soil due to gravity when a NAPL is released into the subsurface, leaving small ganglia along their way [8]. Because of the wide density difference between LNAPLs and air, the vadose zone provides little resistance, allow-ing the LNAPL to enter and accumulate on top of the water table. ...
Laboratory-scale column experimSents were conducted to assess the impact of different LNAPL volumes on LANPL migration behavior in capillary zone in porous media. Three different volumes of diesel (50 mL, 100 mL, and 150 mL) were released in different experiments using a 1D rectangular column filled with natural sand. The water table was set at 29 cm from the bottom of the column. The image analysis results provided quantitative time-dependent data on the LNAPL distribution through the duration for the experiments. Results demonstrated that the higher diesel volume (150 mL) exhibited the faster LNAPL migration through all experiments. This observation was due to the high volume of diesel as compared to other cases which provides high pressure to migrate deeper in a short time. In all experiments, the diesel migration was fast during the first few minutes of observation and then, the velocity was decreased gradually. This is due to pressure exerted by diesel in order to allow the diesel to percolate through the sand voids. Overall, this study proved that the image analysis can be a good and reliable tool to monitor the LNAPL migration in porous media.
... The compounds dissolved in groundwater create large contamination plumes and can be volatilised, remaining within the gaseous matrix or dissolving again in the water (Mackay et al. 2006). The morphology of the contamination source areas is what conditions the plume of volatilised and dissolved contaminants (Pankow and Cherry 1996). In remediation strategies for chlorinated solvents, the source zone is treated in the rst stage, and the plume is treated afterwards (or at the same time).Chemical and physical strategies have mostly been applied as source zone remediation strategies, rather than the biological strategies that are mainly used in the plume (Stroo 2010; Stroo et al. 2012). ...
The chlorinated solvents are among the common groundwater contaminants that show high complexity in their distribution in the subsoil. Microorganisms play a vital role in the natural attenuation of chlorinated solvents. Up to now, how the in situ soil microbial community responds to chlorinated solvents contamination remains unclear. In this study, the microbial community distribution within two boreholes located in the source area of perchloroethene (PCE) were investigated via terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis. Microbial data were related to the lithological and geochemical data and the concentration and isotopic composition of chloroethenes to stablish the key factors controlling the distribution of the microbial communities. The results indicated that Proteobacteria, Actinobacteria and Firmicutes were the most abundant phylums in the sediment. The statistical correlation with the environmental data proved that fine granulometry, oxygen tolerance, terminal electron acceptor processes and toxicity control microbial structure. This study improves our understanding of how the microbial community in the subsoil responds to high concentration of chlorinated solvents.
... These contaminants generally reach groundwater as dense non-aqueous phase liquids (DNAPLs) that can more easily migrate through aquifers than aqueous contaminants (Filippini, 2017). Their denser-than-water nature and their low viscosity have enabled them to penetrate far below the water table in many aquifer systems (Pankow & Cherry, 1996) and to persist for decades (Rivett et al., 2005); they slowly dissolve to yield groundwater plumes that are often extensive (Stefania et al., 2018), in some cases exceeding 10 km in length (Jackson, 1998) and thus acting as diffused pollution (Menichetti & Doni, 2017). ...
This paper describes a forensic investigation of groundwater in an urban context in Italy. The present case study was conducted to detect the hydraulic flow path between a sportfishing pond and a nearby industrial plant’s contaminated groundwater site. The investigation was performed to evaluate the potential for diffusion of contaminants through groundwater flow into a fishing pond located downstream from a chemical factory. High-precision altitude measurements of monitoring stations combined with continuous water level monitoring were crucial to understand the groundwater flow dynamics and define the hydrogeological conceptual model. The study verified that the fishing pond, dug in low-permeability volcanic rock, was not hydraulically connected to the groundwater flow. The presence of contaminants in the pond may be related to the periodic topping-up activity performed using water from an existing well. The identified groundwater flow paths were consistent with the possible contaminant migration from the chemical factory to the water well near the fishing pond.
The potential toxic and carcinogenic effects of chlorinated solvents in groundwater on human health and aquatic ecosystems require very effective remediation strategies of contaminated groundwater to achieve the low legal cleanup targets required. The transition zones between aquifers and bottom aquitards occur mainly in prograding alluvial fan geological contexts. Hence, they are very frequent from a hydrogeological point of view. The transition zone consists of numerous thin layers of fine to coarse-grained clastic fragments (e.g., medium sands and gravels), which alternate with fine-grained materials (clays and silts). When the transition zones are affected by DNAPL spills, free-phase pools accumulate on the less conductive layers. Owing to the low overall conductivity of this zone, the pools are very recalcitrant. Little field research has been done on transition zone remediation techniques. Injection of iron microparticles has the disadvantage of the limited accessibility of this reagent to reach the entire source of contamination. Biostimulation of indigenous microorganisms in the medium has the disadvantage that few of the microorganisms are capable of complete biodegradation to total mineralization of the parent contaminant and metabolites. A field pilot test was conducted at a site where a transition zone existed in which DNAPL pools of PCE had accumulated. In particular, the interface with the bottom aquitard was where PCE concentrations were the highest. In this pilot test, a combined strategy using ZVI in microparticles and biostimulation with lactate in the form of lactic acid was conducted. Throughout the test it was found that the interdependence of the coupled biotic and abiotic processes generated synergies between these processes. This resulted in a greater degradation of the PCE and its transformation products. With the combination of the two techniques, the mobilization of the contaminant source of PCE was extremely effective.
Improved understanding of complex hydrosystem processes is key to advance water resources research. Nevertheless, the conventional way of modeling these processes suffers from a high conceptual uncertainty, due to almost ubiquitous simplifying assumptions used in model parameterizations/closures. Machine learning (ML) models are considered as a potential alternative, but their generalization abilities remain limited. For example, they normally fail to predict accurately across different boundary conditions. Moreover, as a black box, they do not add to our process understanding or to discover improved parameterizations/closures. To tackle this issue, we propose the hybrid modeling framework FINN (finite volume neural network). It merges existing numerical methods for partial differential equations (PDEs) with the learning abilities of artificial neural networks (ANNs). FINN is applied on discrete control volumes and learns components of the investigated system equations, such as numerical stencils, model parameters, and arbitrary closure/constitutive relations. Consequently, FINN yields highly interpretable results. We demonstrate FINN's potential on a diffusion‐sorption problem in clay. Results on numerically generated data show that FINN outperforms other ML models when tested under modified boundary conditions, and that it can successfully differentiate between the usual, known sorption isotherms. Moreover, we also equip FINN with uncertainty quantification methods to lay open the total uncertainty of scientific learning, and then apply it to a laboratory experiment. The results show that FINN performs better than calibrated PDE‐based models as it is able to flexibly learn and model sorption isotherms without being restricted to choose among available parametric models.
The challenges posed by high‐resolution characterization of dense nonaqueous phase liquid (DNAPL) source zone architecture (SZA) have motivated the development of simpler upscaled models that rely on domain‐averaged metrics to capture the average mass discharge downstream of source zones (SZ). However, SZA is highly irregular, making estimation of these domain‐averaged metrics from sparse borehole data extremely difficult. Poor estimation of SZ metrics means that upscaled models cannot reproduce the multistage effluent concentrations. Bayesian inversion methods can be used to obtain accurate estimates of SZ metrics and their uncertainties from sparse data, and from there, upscaled models can better reproduce multistage effluent concentrations. This work presents a framework for integrating a deep‐learning‐based 3D SZA inversion method named Convolutional Variational AutoEncoder—Ensemble Smoother with Multiple Data Assimilation (CVAE‐ESMDA) with a process‐based (PB) upscaled mass‐transfer model. This framework can utilize sparse SZ data to estimate directly mass discharge without multiphase modeling. First, CVAE‐ESMDA estimates the SZA by conditioning on sparse data, which is then used as input in the upscaled model for mass‐discharge estimation. We evaluated our framework on two real and 30 synthetic bench‐scale experiments, with significantly different SZAs and multistage effluent concentrations. The results demonstrate that the CVAE‐based inversion method captures the temporal variations in SZ metrics better than standard ordinary kriging. With the improved SZ metrics, the PB model more accurately reproduces the salient patterns of the multistage mass‐discharge profiles and associated uncertainty. This approach can be used to provide valuable input for risk‐based decision making in remediation applications.
The development of a conceptual site model (CSM) is essential to support decision making for the investigation and remediation of contaminated sites, including sites impacted by dense non‐aqueous phase liquids (DNAPLs). Dynamic investigation strategies using high‐resolution site investigation tools can be used to increase the accuracy, and increase the precision (reduce the uncertainty) of a CSM, while balancing life‐cycle costs. However, the evaluation of CSM accuracy is limited by the hydrogeological and biogeochemical complexities inherent in subsurface systems. This study simulated DNAPL migration, dissolution and reactive transport to create three high‐resolution ‘virtual sites’ composed of 0.4‐1 billion parameter values each, which were investigated by teams of leading practitioners. Use of these virtual sites allowed key hydrogeological and biogeochemical parameters to be known by the model developers but not the investigation teams. Comparison of the CSMs developed by these practitioners to the simulated values across multiple metrics (e.g., dissolved concentrations, DNAPL mass, and mass discharge) showed that 92% of those metrics were estimated within a factor of 10 and 63% were within a factor of 3 of the true (simulated) values. Furthermore, estimates of dissolved phase plume footprint were often more accurate than estimates of DNAPL source footprint, and the approaches used for investigation and data analysis were both important for CSM development. Overall, none of the site investigation approaches used to develop the CSMs resulted in the highest accuracy for all metrics, which demonstrates the need to establish best‐practices that draw from multiple approaches and vary depending on investigation objectives. This article is protected by copyright. All rights reserved.
The use of reactive substances, capable of activating
reductive dehalogenation reactions of chlorinated solvents for
treatment of contaminated aquifers, represents an activity
consolidated in the practice of in-situ remediation. The technique of
Enhanced bioremediation, of extensive experimentation at international level,
has proven to be effective and allows for
achieve the remediation targets through progressive
transformation of pollutants into harmless compounds.
The reactions of reductive dehalogenation, however, depend
also by some factors, mainly the pH of the aquifer and others
geological and hydrogeological characters that must be kept in
consideration for the success of the intervention.
The purpose of this study is to investigate the elution behavior of pool-dominated dense nonaqueous phase liquid (DNAPL) source zone mass during enhanced solubilization remediation. Flow-cell experiments were first conducted to investigate the performance of different solubilization agents on the DNAPL source zone mass removal in porous media. PCE was used as the model organic liquid, while sodium dodecyl sulfate and Tween 80 surfactants, methyl cyclodextrin (MCD) were selected as enhanced-flushing agents. The porous media considered were silica sand and natural calcareous soil. To gain further insight into the dynamics of source zone depletion, the flushing experiments were modeled using two approaches: a multiphase flow model and a simplified empirically based concentration mass discharge (CMD) model. Results of the flushing experiments indicated that the performance of solubilization agents on PCE source zone depletion was in the following order: Tween 80 > SDS > MCD > > Water. Both models reveal the non-ideal behavior observed during the flooding experiments. For all cases considered, the later stage of mass removal appears to be controlled by the portion poorly accessible mass associated with higher-saturation zones. The advantages and limitations of the two modeling approaches are discussed. It is shown that the two modeling approaches are complementary to each other. Whereas the multiphase model can reveal important aspects of the governing pore-scale processes, the latter approach can provide valuable source term depletion metrics, circumventing the need for detailed definition of DNAPL and porous media parameters.
Chlorinated solvents are among the common groundwater contaminants that show high complexity in their distribution in the subsoil. Microorganisms play a vital role in the natural attenuation of chlorinated solvents. Thus far, how the in situ soil microbial community responds to chlorinated solvent contamination has remained unclear. In this study, the microbial community distribution within two boreholes located in the source area of perchloroethene (PCE) was investigated via terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis. Microbial data were related to the lithological and geochemical data and the concentration and isotopic composition of chloroethenes to determine the key factors controlling the distribution of the microbial communities. The results indicated that Proteobacteria , Actinobacteria , and Firmicutes were the most abundant phylums in the sediment. The statistical correlation with the environmental data proved that fine granulometry, oxygen tolerance, terminal electron-acceptor processes, and toxicity control microbial structure. This study improves our understanding of how the microbial community in the subsoil responds to high concentrations of chlorinated solvents.
Environmental forensics consists of a set of defensible scientific methods 2 to address histories and sources of contamination in environment and involves the 3 reconstruction of past environmental events, such as the timing, types and amounts, 4 and sources of chemical releases to the environment. Interrogations necessitating 5 environmental forensic applications usually relate to understanding of the extent, 6 duration, and responsibility for environmental contamination sites in a regulatory 7 and/or legal context. These approaches are also integral to due diligence of environ-8 mental aspects related to mergers, acquisitions and remediation cost recovery. Tech-9 niques such as chemical fingerprinting, chemical fate and transport modeling, hydro-10 geological investigation, and reconstructing operational histories, among others are 11 at the heart of many investigations. These and newer techniques, such as multivariate 12 receptor statistical modeling, continue to evolve and have become more sophisticated 13 over time, as have the types of problems to which they are applied. Scenarios in which 14 environmental forensics have been applied have ranged from remote Arctic environ-15 ments to urban sediments. In both extreme scenarios, the chemical condition of the 16 environment—i.e., the background or baseline—is a central part of any investiga-17 tion. It is upon this background that additional contamination from one or several 18 responsible methods may be juxtaposed. The types of problems to which environ-19 mental forensic techniques are commonly applied include: identifying and quanti-20 fying contributions from various sources to contaminated sites, distinguishing natural 21 background and diffuse anthropogenic background from specific pollution sources, 22 differentiating specific sources of petroleum and natural gas, delineating time frames.
Chlorinated ethene contaminated soils of low and high permeability differ in characteristics, challenges, and thereby requirements for remediation. Using electric currents to remediate chlorinated ethenes may overcome some of the challenges currently faced during remediation in low‐ and high‐permeability soils. However, even for electric remediation, the relevant processes in these zones of different permeabilities vary significantly. In low‐permeability soils, electrokinetics offer advantages due to improved transport and deliver reactants for subsequent degradation of chlorinated ethenes. In high‐permeability soils, electrochemically generated reactants can transform chlorinated ethenes directly. This chapter describes electrokinetic and electrochemical remediation strategies and their related degradation pathways of chlorinated ethenes to remediate low‐ and high‐permeability soils. The current state of development, focusing on field applications, is presented and demonstrates promising potential for electrokinetic and electrochemical remediation of sites contaminated with chlorinated ethenes.
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