Contaminant Plume Research Articles

Contaminant transport model in transient and unsaturated conditions applied to laboratory column test with tailings

Mining is an important economic activity in the modern world. However, despite the generated benefits, mining produces tremendous volumes of tailings, an environmental liability with numerous adverse effects. Researches about contaminant transport in tailings dam are important to assess the degree of contamination and to propose preventive or remedial measures. In geotechnical practice, the flow of solutes is generally characterized by numerical solution of the Richards equation to describe water movement followed by advection-dispersion equation to describe contaminant movement. This study aimed to model and simulate contaminant transport in a laboratory column test, using a new analytical formulation and mathematical codes, through tailings in transient unsaturated conditions. The analytical solution for the Richards equation was used to simulate the variation in the volumetric water content and to determine the transient contaminant plume using the advection-dispersion equation subsequently. The models were used to calibrate experimental data from hydraulic characterization and contamination tests. Finally, the normalized contaminant plume (cw/c0) was simulated as a function of time and space. Comparisons with experimental data showed that the analytical formulations adequately expressed the process of contaminant infiltration through the unsaturated porous medium. The formulations offered effectively and are configured as a new approach to solve various contamination problems in transient unsaturated conditions, providing insights into many complex processes that occur in the lab tests and requires far less computational effort compared with current programs to modeling the solute transport using numerical solutions, as the versatile commercial Software HYDRUS.

Forecasting Groundwater Contaminant Plume Development Using Statistical and Machine Learning Methods

AbstractForecasting groundwater contaminant plume development is critical for determining risks to downgradient receptors and predicting the time to site closure. However, accurate forecasts are a formidable challenge due to the complexities of a heterogeneous subsurface. While historically groundwater well data in combination with numerical flow models have been used for this task, the advent of machine learning offers new data‐driven opportunities for improving contaminant fate and transport predictions. In this study, we interrogate the viability of two forecasting models—Prophet and damped Holt's exponential smoothing model—for predicting groundwater contaminant plume development. The impacts of spatial and temporal data density on the accuracy of the forecasts are evaluated. For wells with declining contaminant concentrations, the damped Holt's method achieves more accurate forecasts. However, only Prophet allows for the inclusion of exogenous regressors, enabling predictions of future declining trends in wells with still increasing contaminant concentrations. Application of these models does not only require robust training data, but also an understanding of model biases. Overall, powerful data‐driven models are already available for contaminant plume prediction, but groundwater sampling approaches will have to improve, for instance, through the collection of real‐time spatial and temporal high‐resolution data, to take full advantage of their capabilities.

Contaminant source characterization in a coastal aquifer influenced by tidal forces and density-driven flow

Contaminant source characterization (CSC) plays an important role in environmental forensics and pollution control. Past studies commonly solve the CSC problem in case studies where simple groundwater velocity fields (with e.g. parallel velocity vectors) prevail under steady state conditions. A few studies have addressed CSC in cases where the effect of heterogeneity or wells causes the velocity vectors to deviate from a parallel alignment. More complex transient velocity fields are yet to be addressed in groundwater CSC studies. One key example is coastal aquifers, where density-driven flow and the effect of oceanic forces (e.g. tides and waves) create complex transient velocity fields that lead to deformation of contaminant plumes and enhance mixing processes. The present paper aims to address this challenge by developing and validating a novel solution method for CSC in a coastal aquifer under the effect of tidal forces and density-driven flow. For this purpose, the study combines a numerical model of density-dependent flow and multiple-species solute transport, artificial neural networks, and a customized Kalman filtering technique, termed the ‘constrained restart dual ensemble Kalman filter’ (CRD-EnKF). In this approach, the time series of contaminant concentration downgradient of the source, and salinity concentrations in the transition zone between fresh and saline groundwater is employed for the estimation of contaminant source location and strength. We validated the proposed methodology by using a benchmark problem of a coastal aquifer with sloping beach and tide-induced pressure oscillation at the sea boundary.

Pollution simulation and remediation strategy of a zinc smelting site based on multi-source information

Contaminated sites pose a significant risk to human health and the regional environment. A comprehensive study was dedicated to improving the understanding of the contamination condition of a smelting site by integrating multi-source information through 3D visualization techniques. The results showed that 3D visualization reveals excellent potential for application in the environmental studies to finely depict contamination in soils and establish relationships with geological features, hydrological conditions, and sources of contamination. The contamination plume model revealed that the soil environment at the site was seriously threatened by toxic metals, and dominated by multi-metal contamination, with contamination soil volume ranked as Cd > As > Pb> Zn > Hg. The stratigraphic model revealed the heterogeneous geological conditions of the site and identified the mixed fill layer as the primary remediation soil layer. The permeability model revealed that soil permeability significantly influenced contamination dispersion and contributed to delineate the contamination boundary accurately. The ecological hazard model targeted the high ecological hazard area and determined the high hazard contribution of Cd and Hg in the site soil. The outcomes can be directly applied to actual site remediation and provide a reference for the contaminated sites evaluation and restoration in the future.

Natural Biodegradation of Vinyl Chloride and cis-Dichloroethene in Aerobic and Suboxic Conditions.

Chlorinated ethene (CE) groundwater contamination is commonly treated through anaerobic biodegradation (i.e., reductive dechlorination) either as part of an engineered system or through natural attenuation. Aerobic biodegradation has also been recognized as a potentially significant pathway for the removal of the lower CEs cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). However, the role of aerobic biodegradation under low oxygen conditions typical of contaminated groundwater is unclear. Bacteria capable of aerobic VC biodegradation appear to be common in the environment, while aerobic biodegradation of cDCE is less common and little is known regarding the organisms responsible. In this study, we investigate the role of aerobic cDCE and VC biodegradation in a mixed contaminant plume (including CEs, BTEX, and ketones) at Naval Air Station North Island, Installation Restoration Site 9. Sediment and groundwater collected from the plume source area, mid-plume, and shoreline were used to prepare microcosms under fully aerobic (8mg/L dissolved oxygen (DO)) and suboxic (< 1mg/L DO) conditions. In the shoreline microcosms, VC and cDCE were rapidly degraded under suboxic conditions (100% and 77% removal in < 62days). In the suboxic VC microcosms, biodegradation was associated with a > 5 order of magnitude increase in the abundance of functional gene etnE, part of the aerobic VC utilization pathway. VC and cDCE were degraded more slowly under fully aerobic conditions (74% and 30% removal) in 110days. High-throughput 16S rRNA and etnE sequencing suggest the presence of novel VC- and cDCE-degrading bacteria. These results suggest that natural aerobic biodegradation of cDCE and VC is occurring at the site and provide new evidence that low (< 1mg/L) DO levels play a significant role in natural attenuation of cDCE and VC.

Imaging acidic contaminants in a confined aquifer using electromagnetic geophysical method constrained by hydrochemical data

Acid in-situ uranium leach mining is an effective, popular technology for extracting uranium without large uranium mill tailings. However, acid in-situ leaching causes extremely high concentrations of acidic contaminants in aquifers. To represent the migration and range of acidic contaminant pollutants in confined aquifers, this study applied the controlled source audio-frequency magnetotellurics (CSAMT) method to a uranium mining area located in the Yili Basin, Xinjiang, northwest China. We collected ten CSAMT profiles from 364 sites with an average site interval of 20 m. The electrical resistivity model of the uranium mining area was obtained via two-dimensional inversion using CSAMT data, with 23 frequencies, ranging from 8192 Hz to 4 Hz. Combined with geological, geochemical, and well log data, this resistivity model was successfully used to identify the scale and position of acid contaminant plumes beneath the uranium mining area, which appear as electrically well-defined features that closely coincide with the distribution of sulfate and uranium ions in groundwater. With uranium mining activities ceasing, the scale of acid contaminant plumes has been reduced, owing to the natural attenuation of the aquifer or the contaminants well confined in the mining site. The low-permeability sandstone surrounding the aquifer was imaged as a resistive feature, which confines the contaminant plumes to the uranium mining area and slows the downstream migration of contaminants. According to the modified Archie's law, the porosity of the sandstone bearing uranium beneath the injection well zone increases, owing to acidification, while the porosity of the sandstone beneath the production well zone decreases, owing to pore plugging.

Evolution of LNAPL contamination plume in fractured aquifers

The LNAPL contamination affecting an industrial area of southeastern Sicily (Italy) is reported herein as a case study to analyze some peculiarities on its spatial evolution. The free-phase product of light hydrocarbons, leaked from a tank, deserved investigations due to its anomalous migration trend, which was not consistent with the static groundwater flow direction of the area. The collection of geological and hydrogeological data and their organization into a GIS database allowed reconstructing the evolutionary stage of the plume within the 2014–2020 time interval, providing some explanation to the scientific problem. The supernatant thickness was compared with the groundwater oscillation, leading to consideration on the aquifer typology. The causes of the peculiar migration trend were found in three main factors, among which the geological and geostructural ones gain a key relevance. Achieved results show that the rock mass fracturing and the presence of underground structures, probably of tectonic origin, are responsible in driving the contamination plume through a preferential path under the dynamic condition induced by anthropic activities. This supports the need of underground geological and geostructural knowledge when dealing with similar issues and when designing specific remediation measures; the case study presented herein demonstrates that the correct location of remedial measures is crucial for reclamation purposes. Furthermore, data were statistically analyzed looking for a relation between real and apparent supernatant thickness. Prediction equations, for a quick estimation of the contamination entity in such type of aquifers, are presented providing hints for future studies on other settings worldwide.

Health Risk Assessment for the Residential Area Adjacent to a Former Chemical Plant.

A health risk assessment was carried out for the residents of Łęgnowo-Wieś settlement adjacent to a former Zachem Chemical Plant, Bydgoszcz, Poland. Due to the unique Zachem site history and contamination profile, an innovative strategy for soil sampling and contaminant selection was applied. The novelty in the developed strategy consisted of selecting substances for the health risk assessment, taking into consideration the location and boundaries of the groundwater contamination plumes in relation to contamination sources. This allowed limiting the number of the analysed contaminants. The risk assessment focused on the surface soil of a residential area, which was divided into 20 sampling sectors and 6 backyards with wells from which water was used for watering edible plants. A total of 80 inorganic and organic substances were determined, including metals, phenol, aniline, BTEX, diphenyl sulphone, chloroaniline, epichlorohydrin, hydroxybiphenyl, nitrobenzene, octylphenols, toluenediamine, toluidine, 16 polycyclic aromatic hydrocarbons, tetrachloroethylene and trichloroethylene. For the health risk assessment, the United States Environmental Protection Agency’s deterministic method was applied. This applies conservative assumptions to obtain risk estimates protective for most of the potential receptors. Three exposure pathways were analysed: (1) incidental soil ingestion, (2) dermal contact with soil and (3) inhalation of fugitive soil particles and volatiles. In all sampling sectors and backyards, the total non-cancer risks (hazard index) were significantly lower than the acceptable level of 1. The acceptable cancer risk level for the single carcinogen of 1 × 10−5 was only insignificantly exceeded in the case of benzo(a)pyrene in three sectors and one backyard. The total cancer risks were lower than the acceptable level of 1 × 10−4 in all sampling sectors and all backyards. The findings show that the soil in the entire residential area is safe for the residents’ health and no remedial actions are required. However, since not all possible exposure pathways were analysed in this study, further research focused on assessing the health risk resulting from the consumption of locally grown food is strongly recommended.

Reactive transport modeling for supporting climate resilience at groundwater contamination sites

Abstract. Climate resilience is an emerging issue at contaminated sites and hazardous waste sites, since projected climate shifts (e.g., increased/decreased precipitation) and extreme events (e.g., flooding, drought) could affect ongoing remediation or closure strategies. In this study, we develop a reactive transport model (Amanzi) for radionuclides (uranium, tritium, and others) and evaluate how different scenarios under climate change will influence the contaminant plume conditions and groundwater well concentrations. We demonstrate our approach using a two-dimensional (2D) reactive transport model for the Savannah River Site F-Area, including mineral reaction and sorption processes. Different recharge scenarios are considered by perturbing the infiltration rate from the base case as well as considering cap-failure and climate projection scenarios. We also evaluate the uranium and nitrate concentration ratios between scenarios and the base case to isolate the sorption effects with changing recharge rates. The modeling results indicate that the competing effects of dilution and remobilization significantly influence pH, thus changing the sorption of uranium. At the maximum concentration on the breakthrough curve, higher aqueous uranium concentration implies that sorption is reduced with lower pH due to remobilization. To better evaluate the climate change impacts in the future, we develop the workflow to include the downscaled CMIP5 (Coupled Model Intercomparison Project) climate projection data in the reactive transport model and evaluate how residual contamination evolves through 2100 under four climate Representative Concentration Pathway (RCP) scenarios. The integration of climate modeling data and hydrogeochemistry models enables us to quantify the climate change impacts, assess which impacts need to be planned for, and therefore assist climate resiliency efforts and help guide site management.

Evaluation of 1,4-dioxane attenuation processes at the Gelman Site, Michigan, USA

1,4-Dioxane released at the Gelman Site in Washtenaw County, Michigan, produced a series of contaminant plumes migrating up to 3 km through a heterogenous glacial aquifer system. An analysis of 1,4-dioxane concentrations in the Eastern Area of the Gelman Site between 2011 and 2017 documented a mass balance deficit of 2200 kg in excess of 2100 kg of 1,4-dioxane removed via remediation. Five mechanisms were evaluated to account for the mass deficiency: sorption, matrix diffusion, biodegradation, surface discharge, and bypass of the existing monitoring well network.The mass of 1,4-dioxane sorbed to aquifer and aquitard materials and the mass of 1,4-dioxane diffused into low permeability zones were estimated. However, decreasing aqueous concentrations across most of the contaminated area between 2011 and 2017 are expected to induce desorption and back diffusion during this period. Surface water discharge to a storm drain in the downgradient portion of the site was analyzed using concentration measurements and stream gage data. Results suggest that 1,4-dioxane mass entering the drain during the period between 2011 and 2017 was insufficient to account for the mass deficiency.Although available geochemical measurements indicate predominantly anaerobic aquifer conditions at the Gelman Site, biodegradation of 1,4-dioxane was estimated using first order decay rate constants from other sites where conditions may be more favorable. Results suggest that biodegradation could explain some but not all of the missing mass.Bypass of the downgradient monitoring well network is the most parsimonious explanation for the 1,4-dioxane mass deficit. This conclusion is supported by documented flow path complexity through the aquifer system and the sparse density of monitoring wells in the downgradient Eastern Area. These findings underscore the importance of characterizing aquifer heterogeneity when modeling and remediating persistent groundwater contaminants such as 1,4-dioxane.

A comparative study of the sorption of O-PAHs and PAHs onto soils to understand their transport in soils and groundwater

Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivates (O-PAHs) are identified in soils and groundwater of industrialized sites and contribute to the risk for Humans and the Environment. Nevertheless, data are scarce in literature concerning their retention and transfer in soils and no soil - water partition coefficients are available for these compounds. Sorption of two PAHs, fluorene and acenaphthene and two O-PAHs, 9H-fluorenone and dibenzofuran onto two soils with different organic carbon contents was evaluated and compared by determining their sorption isotherms. Effect of ionic strength and liquid to solid ratio, on fluorene and fluorenone sorption was also evaluated. Sorption equilibrium is achieved within less than 24 hr of mixing and linear sorption models best fit the isotherm data. Acenaphthene and dibenzofuran are similarly sorbed onto the soil. KD of fluorene is higher than the one of fluorenone, showing a smaller affinity of fluorenone towards the solid phase. This means that O-PAH could form larger contamination plumes in groundwater than PAHs. Decreasing the L/S ratio from 100 to 50 and 30, increases the sorption of fluorenone onto the soil by 56% and 67% respectively, while the sorption of fluorene is slightly increased. Increasing the ionic strength of the aqueous phase also modifies the sorption of fluorenone, contrary to the sorption of fluorene which is slightly affected.

Effect of biostimulation and bioaugmentation on biodegradation of high concentrations of 1,4-dioxane.

1,4-Dioxane is a pervasive and persistent contaminant in numerous aquifers. Although the median concentration in most contaminant plumes is in the microgram per liter range, a subset of sites have contamination in the milligram per liter range. Most prior studies that have examined 1,4-dioxane concentrations in the hundreds of milligrams per liter range have been performed with industrial wastewater. The main objective of this study was to evaluate aerobic biodegradation of 1,4-dioxane in microcosms prepared with soil and groundwater from a site where concentrations range from ~ 1500mg·L-1 in the source zone, to 450mg·L-1 at a midpoint of the groundwater plume, and to 6mg·L-1 at a down-gradient location. Treatments included biostimulation with propane, addition of propane and a propanotrophic enrichment culture (ENV487), and unamended. The highest rates of biodegradation for each location in the plume occurred in the bioaugmented treatments, although indigenous propanotrophs also biodegraded 1,4-dioxane to below 25µg·L-1. Nutrient additions were required to sustain biodegradation of propane and cometabolism of 1,4-dioxane. Among the unamended treatments, biodegradation of 1,4-dioxane was detected in the mid-gradient microcosms. An isolate was obtained that grows on 1,4-dioxane as a sole source of carbon and energy and identified through whole-genome sequencing as Pseudonocardia dioxivorans BERK-1. In a prior study, the same strain was isolated from an aquifer in the southeastern United States. Monod kinetic parameters for BERK-1 are similar to those for strain CB1190.

Geophysical and Geochemical Characterization of Solidwaste Dumpsite: A Case Study of Chowa Gujar, Peshawar (Part of Indus Basin)

Open and non-engineered dumping is a typical method for solid waste disposal in most cities of Pakistan. This practice of waste dumping poses a serious threat to the surrounding ecosystem and human population due to the release and transport of decomposed organic matter, i.e., leachate from dumpsite into the groundwater. The present study was conducted over a non-engineered and open dumpsite (Chowa Gujar), located in the outskirts of the highly populated city of Peshawar by using integrated geophysical techniques such as electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) and geochemical techniques. The main goal was to delineate the characterization and depth of buried waste, to map the subsurface extension of contaminant plumes towards agricultural land and groundwater table and the concentration of heavy metals (HMs) in dump and agricultural soil. Geophysical results showed that the thickness of buried waste (predominantly composed of domestic waste) was around 4 m and the leachate plumes have percolated to the adjacent agricultural land. A range of heavy metals (mg/kg) such as Cr (20.5–26.6), Cd (2.6–5.7), Pb (0.35–21.25), Ni (2.5–53.05), Cu (29–68.3), Zn (45.7–77), and Co (18.9–23.2) have been found in the agricultural land adjacent to the dumpsite. The findings demonstrated that combined use of ERT and GPR successfully characterize the buried waste and spread of pollutant plumes spatially and vertically from Chowa Gujar dumpsite. The anomalous geophysical signatures were confirmed by geochemical characterization. The movement of leachate plumes towards agricultural land and groundwater table and the concentration of HMs in soil show that Chowa Gujar dumpsite is a potential source of contamination not only to the surrounding population but also to the agricultural land, surface (Bara River), and subsurface water bodies. In the study region, there is an urgency to take remediation and mitigation measures to reduce the level of pollution created by the dumpsite.

Characterization of the Dynamics of Leachate Contamination Plumes in the Surroundings of the Hulene-B Waste Dump in Maputo, Mozambique

The contamination of areas around solid urban waste dumps is a global challenge for the maintenance of environmental quality in large urban centres in developing countries. This study applied a geophysical method (electrical resistivity) to identify leachate contamination plumes in the subsoil and groundwater, as well as to describe their temporal dynamics (2020 and 2021) in the surroundings of the Hulene-B waste dump, Maputo, Mozambique. Eight 400 m electrical resistivity profiles were performed, four profiles in January 2020 and four profiles in May 2021 overlapped, and the data were inverted with RES2D software. The electrical resistivity models predominantly indicate an E-W movement of large contamination plumes that are successively diluted with saturated media and groundwater, creating zones of less resistive anomalies (&lt;4.2–8.5 Ω·m) possibly contaminated at the two analysed seasons, between 2020–2021. The thickness of the contamination plumes was higher in summer (2020) for profiles 1 and 2, and we associate it with the production and migration mechanisms of leachate that are intense in the hot and rainy season. Southwest of the dump, profile 4b showed the propagation of anomalous areas on the surface and at depth, which are associated with the production of leachate resulting from the continuous decomposition of waste that is continuously deposited in a new area southwest of the dump, thus generating a slow and continuous migration of leachate at depth, mainly in winter (2021). The spatial distribution of contamination plumes during both seasons was reduced significantly farther away from the waste deposit, revealing the attenuating effect of groundwater and lithological substrate (Profile 3).

Approximately consistent SPH simulations of the anisotropic dispersion of a contaminant plume

Approximately consistent SPH simulations of the anisotropic dispersion of a contaminant plume

Reuse of residues/wastes as a sustainable solution for landfill leachate contaminated groundwater

In order to increase the reuse of wastes and residues, as required by the Waste Framework Directive, the potential use of waste, residue and natural minerals as low-cost permeable reactive barrier (PRB) materials was investigated. The performance of a kitchen waste compost, sepiolite and steel slag was compared with that of volcanic slag, pumice and activated carbon in removing specific contaminants from landfill leachate. The experiments represented that the activated carbon removed 27% of the ammonium (NH4+), 75% of the chemical oxygen demand (COD) and 100% of the phosphate (PO43–), zinc (Zn2+) and nickel (Ni2+) from the landfill leachate. Volcanic slag exhibited removal efficiencies of 50% COD and 100% PO43– and pumice exhibited removal efficiencies of 20% NH4+, 27% Zn2+, 65% COD and 100% PO43–. The reactive materials were also checked for their potential in releasing unwanted constituents and represented different levels of the solute (e.g., PO43–, SO42–, NH4+) release. Among the reactives, sepiolite was found to be the reactive material reflecting a minor release (e.g., Zn2+, Cd2+ and Ni2+), but also delivering removal efficiencies of 40, 50, 65, 95, 97, 98, 98 and 100% for Ni2+, COD, Zn2+, SO42–, Cl–, F–, NH4+ and PO43–, respectively. The results show that the studied materials have the potential as reactives for PRB systems treating high strength contaminant plumes.

ОЦІНКА БАГАТОРІЧНИХ ПРОСТОРОВО-ЧАСОВИХ ЗМІН ХІМІЧНОГО СКЛАДУ ПІДЗЕМНИХ ВОД У ЗОНІ ВПЛИВУ КОЛИШНЬОГО УРАН-ПЕРЕРОБНОГО ПІДПРИЄМСТВА ВО «ПРИДНІПРОВСЬКИЙ ХІМІЧНИЙ ЗАВОД»

This study provides an analysis of data from long-term (2005-2021) observations of the chemical composition of groundwater in the impact zone of the former uranium ore processing enterprise (Production Union Prydniprovskyi Chemical Plant (PU “PChP”) in the city of Kamianske, in particular, areas of near-surface tailings of uranium ore processed residues (“Zapadnoe”, “Central Yar” and others). All tailings on the site of the former PU “PChP” were built without installation of anti-permeable barriers, and therefore under the influence of atmospheric precipitation, the water, formed in the tailings body, highly contaminated of uranium series radionuclides and residues of chemical reagents, can penetrate to the groundwater aquifers, with which they spread beyond the limits of their technological localization in tailings. In addition, the entire territory of the former industrial site of mining and chemical production “PChP” is a complex of former enterprises, septic tanks, production waste holding sites, warehouses of chemical reagents and residues of former production, which are also sources of man-made pollution of the territory and influence on chronic pollution of groundwater. Therefore, environmental monitoring programs in the impact zone of tailings impoundments included not only monitoring of indicators of the content of uranium series radionuclides in elements of the natural environment, but also studying of the chemical composition of waters. The analysis of observation data during the period from 2005 to 2021 was carried out in order to assess the extent of the spread of polluted waters beyond the limits of the location of the tailings ponds, to identify major macroions in the composition of groundwater as indicators for assessing the spread of the contamination plume beyond the boundaries of the tailings ponds, as well as to identify patterns of formation the groundwater quality within the site under the influence of man-made and natural factors. It is shown that the mineralization of groundwater, as well as its chemical composition, significantly changed as the sampling site moved away from the tailings. Changes in the chemical composition of water and the dominant content of the major macroions at different distances from the tailing’s ponds made it possible to determine the difference in the characteristics of the influence of infiltration waters from the source of the tailing’s ponds and scattered sources of pollution within the boundaries of the PChP site along the groundwater flow line. The main factors of uncertainty in the estimations of the formation of groundwater chemistry in the zone of the industrial complex are shown, which must be taken into account for the development of the network of monitoring observations.

A pilot study characterizing tetrachloroethylene exposure with exhaled breath in an impacted community

Martinsville, Indiana overlays four groundwater contamination plumes, including a U.S. Environmental Protection Agency (EPA)-designated Superfund site. The primary contaminants are tetrachloroethylene (PCE), trichloroethylene (TCE), and other volatile organic compounds (VOCs). Martinsville represents many similar communities facing the challenge of groundwater and soil contamination and vapor intrusion, where residents are often frustrated by the lack of help in understanding and addressing the problem. The objective of this study was to evaluate PCE in exhaled breath to identify and quantify exposure to PCE and to explore the extent and level of PCE exposure among community residents. We measured chlorinated VOCs in exhaled breath samples from 38 healthy individuals who lived either in a contamination area or outside any plume area. We also measured VOCs in indoor air and tap water samples collected from 10 homes. PCE was detected in all exhaled breath samples (mean: 6.6 μg/m3; range: 1.9–44 μg/m3) and tap water samples (mean: 0.74 μg/L; range: 0.39–0.92 μg/L). PCE was detected in six of nine (66%) homes with air concentrations ranging from 1.6 to 70 μg/m3, exceeding the EPA action level of 42 μg/m3. We did not detect TCE or any other chlorinated VOCs in these samples. PCE exposure occurred among individuals living on the EPA Superfund site, as well as among those living on other plume sites and those living outside any known plumes. Preventive measures should focus on identifying highly exposed groups and reducing their exposures, followed by addressing moderately elevated exposures in the community. Our results demonstrated that PCE in exhaled breath can be used as an effective tool in community engaged environmental health research to evaluate the extent and level of community exposure, increase awareness, and promote residents’ participation in research and site cleanup decision-making.

Remediation Potential of Borehole Thermal Energy Storage for Chlorinated Hydrocarbon Plumes: Numerical Modeling in a Variably-Saturated Aquifer

Underground thermal energy storage is an efficient technique to boost the share of renewable energies. However, despite being well-established, their environmental impacts such as the interaction with hydrocarbon contaminants is not intensively investigated. This study uses OpenGeoSys software to simulate the heat and mass transport of a borehole thermal energy storage (BTES) system in a shallow unconfined aquifer. A high-temperature (70 C) heat storage scenario was considered which imposes long-term thermal impact on the subsurface. Moreover, the effect of temperature-dependent flow and mass transport in a two-phase system is examined for the contaminant trichloroethylene (TCE). In particular, as subsurface temperatures are raised due to BTES operation, volatilization will increase and redistribute the TCE in liquid and gas phases. These changes are inspected for different scenarios in a contaminant transport context. The results demonstrated the promising potential of BTES in facilitating the natural attenuation of hydrocarbon contaminants, particularly when buoyant flow is induced to accelerate TCE volatilization. For instance, over 70% of TCE mass was removed from a discontinuous contaminant plume after 5 years operation of a small BTES installation. The findings of this study are insightful for an increased application of subsurface heat storage facilities, especially in contaminated urban areas.

Migration of Co, Cd, Cu, Pb to the groundwater in the area of underground coal gasification experiment in a shallow coal seam in the experimental mine ‘Barbara’ in Poland

A numerical model of inorganic pollutants migration in the area of ​​ underground coal gasification (UCG) reactor in the post-operational phase was constructed in this study. Also the deceleration of migration and the shape of the contaminant plume in individual geological formations of the reactor surroundings, resulting from different values ​​of sorption affinity, were compared. The simulations were carried out for four selected metals (Co, Cd, Cu, Pb), which in relation to the raw coal and post-process char showed different sorption properties. The sorption parameters of the tested systems were determined experimentally on the basis of the Freundlich isotherm equation. The retardation coefficients were calculated and the degree of sorption intensity in hydrogeological media was classified from II (in the cobalt-char and metals-coal systems) to the IV class of sorption intensity (in the copper-char system).The modeling was carried out using the finite element method (FEM) in the COMSOL Multiphysics computing environment in a two-dimensional plane. The simulation of pollutant migration was carried out for the transient state, with the assumed time horizon up to 20 years after the termination of the UCG experiment. The bottom of the cavity formed due to the coal gasification in situ (10 m × 20 m ellipse) was assumed as the source of contamination and the spread of metals in a horizontal plane 200 m long and 200 m wide was analyzed.To compare the extent to which sorption phenomena affect the spread of pollutants, an additional model was constructed, taking into account only the advection–dispersion movement of the contaminant plume. The consequence of sorption interactions for the tested systems was the delay of the contaminant plume migration depending on time since the termination of the gasification process and depending on the distance from the source of pollution. Due to high sorption affinities, the post-process char acts as an effective buffer for inorganic pollutants and slows down the migration of analyzed metals even 20 years after UCG experiment. The greatest slowdown in migration in relation to the velocity of groundwater flow as a result of sorption occurred for copper transport in the char layer.